Reproductive Anatomy, Physiology & the Menstrual Cycle - Cheat Sheet
Your last-minute revision companion for the reproductive system chapter. This cheat sheet condenses ALL exam-critical anatomy, hormones, cycle phases, and high-yield clinical facts into one rapid-reference guide. Review the must_remember section and diagrams first.
Male Reproductive Anatomy & Spermatogenesis
Formulas
Sperm survival time = 48–72 hours (up to 5 days in fertile cervical mucus)
Meaning
Duration sperm remain viable in the female reproductive tract
Watch out
Students often say sperm only last 24 hours — WRONG. They survive 48–72 hours routinely, and up to 5 days in optimal conditions.
When to use
When calculating fertile window or explaining conception risk
Spermatogenesis duration = 64–74 days
Meaning
Time from spermatogonium to mature, motile sperm
Watch out
Common error: confusing spermatogenesis time with sperm transit time through epididymis (~12 days).
When to use
Explaining why testicular damage (fever, chemotherapy) affects sperm count only weeks later
Normal sperm concentration ≥15 million/mL (WHO reference)
Meaning
Minimum concentration in a normal ejaculate
Watch out
Some old standards used 20 million/mL; use ≥15 million/mL for current NLE.
When to use
Interpreting semen analysis results; defining male factor infertility
Ejaculate volume = 2–5 mL per ejaculation
Meaning
Normal volume of semen expelled during orgasm
Watch out
Low volume (<1.5 mL) suggests prostate or seminal vesicle dysfunction; high volume does NOT mean high fertility.
When to use
Assessing male fertility or sexual dysfunction
Common values
Value
33–34°C (1–2°C below core body temperature of ~37°C)
Symbol
T
Quantity
Scrotum temperature
Value
64–74 days
Symbol
t
Quantity
Spermatogenesis duration
Value
≥15 million/mL (WHO reference)
Symbol
[S]
Quantity
Normal sperm concentration
Value
2–5 mL
Symbol
V
Quantity
Ejaculate volume
Value
~12 days
Symbol
t_epi
Quantity
Epididymal transit time
Important facts
- Sperm are produced continuously from puberty until old age; no decline in total number, but motility and morphology decline with age.
- Each sperm carries EITHER an X or Y chromosome — the father determines fetal sex.
- Seminal vesicles contribute ~60% of semen volume; a fructose-rich, alkaline fluid nourishes sperm.
- Prostate gland (surrounds urethra) secretes thin, alkaline fluid that neutralises vaginal acidity and aids sperm motility.
- Bulbourethral (Cowper's) glands release pre-ejaculate that lubricates the urethra and can contain sperm (basis for pre-ejaculatory pregnancy risk).
- During ejaculation, a reflex closes the bladder neck to prevent retrograde ejaculation (no simultaneous urine and semen).
- Cryptorchidism (undescended testicle) causes infertility if bilateral or bilateral effects; must be corrected by ~2 years to prevent permanent damage.
Key definitions
Spermatogenesis
Example
A male with fever in January will have reduced sperm count by March because spermatogenesis is ongoing.
Continuous production of mature sperm from spermatogonia in seminiferous tubules, driven by FSH and testosterone, taking 64–74 days.
Leydig (interstitial) cells
Example
Damage to Leydig cells from cryptorchidism or heat reduces testosterone production.
Endocrine cells in the testis that secrete testosterone in response to LH stimulation.
Sertoli cells
Example
FSH stimulates Sertoli cells to produce anti-müllerian hormone (AMH), used to assess ovarian reserve in females.
Support cells in seminiferous tubules that nurture developing sperm and respond to FSH.
Epididymis
Example
Sperm emerging from seminiferous tubules are immotile; they gain motility in the epididymis over ~12 days.
Coiled duct on each testis where sperm mature, gain motility, and are stored; site of vasectomy.
Vas (ductus) deferens
Example
Post-vasectomy, sperm are still produced but blocked from ejaculation; stored sperm are reabsorbed.
Muscular duct carrying mature sperm from epididymis to ejaculatory duct; cut and tied in vasectomy.
Scrotum temperature
Example
Cryptorchidism (undescended testicle) or prolonged fever impairs sperm production due to elevated temperature.
About 1–2°C below core body temperature (~33–34°C), required for normal spermatogenesis.
Diagrams to know
- Sagittal cross-section of male pelvis showing testes, epididymis, vas deferens, seminal vesicles, prostate, and bulbourethral glands.
- Cross-section of seminiferous tubule showing spermatogonium, primary spermatocyte, secondary spermatocyte, spermatid, and mature sperm.
- Pathway of sperm: spermatogonium → primary spermatocyte → secondary spermatocyte → spermatid → mature sperm (released into lumen).
Female Reproductive Anatomy
Common values
Value
~10 cm
Symbol
L_tube
Quantity
Fallopian tube length
Value
3.5–4.5
Symbol
pH_vagina
Quantity
Vaginal pH
Value
~12.5 cm (estimates obstetric conjugate)
Symbol
DC
Quantity
Diagonal conjugate
Value
~11 cm (cannot be measured clinically; estimated from diagonal conjugate)
Symbol
OC
Quantity
Obstetric (true) conjugate
Value
1–2 million
Symbol
N_birth
Quantity
Oocytes at birth
Value
~400,000
Symbol
N_puberty
Quantity
Oocytes at puberty
Value
~400
Symbol
N_lifetime
Quantity
Oocytes ovulated in lifetime
Important facts
- Uterus is normally anteverted (tilted forward) and anteflexed (bent forward); retroversion is a normal variant.
- Vaginal pH is normally acidic (3.5–4.5) to protect against infection; Döderlein's lactobacilli maintain this; douching disrupts flora.
- Fallopian tubes are ~10 cm long; fertilisation occurs in the ampulla (outer third); ovum travels 3–4 days to reach uterus.
- Oocytes are surrounded by follicle cells; primary oocyte is arrested in prophase I of meiosis I until ovulation.
- At ovulation, the secondary oocyte (with 1st polar body) is released; fertilisation triggers completion of meiosis II.
- Diagonal conjugate (~12.5 cm) and obstetric conjugate (~11 cm) estimate pelvic adequacy; contractions increase cephalopelvic disproportion risk.
- Gynecoid pelvis (rounded inlet, wide subpubic angle ~80°) is ideal for vaginal delivery; android, platypelloid, and anthropoid are less favourable.
- Bartholin's glands (greater vestibular glands) secrete mucus for lubrication; cysts can form if duct is blocked.
- Clitoris is homologous to penis; erectile tissue, highly innervated and sensitive; plays no reproductive role in conception.
Key definitions
Vulva
Example
Perineal lacerations during childbirth are classified by degree (1°–4°); a 4° laceration extends to the anal sphincter.
External female genitalia including mons pubis, labia majora/minora, clitoris, vestibule, urethral/vaginal openings, Bartholin's glands, and perineum.
Vagina
Example
Douching destroys vaginal flora and increases risk of bacterial vaginosis and pelvic inflammatory disease (PID).
Muscular, elastic canal (birth canal, menstrual flow passage, coitus organ); naturally acidic (pH 3.5–4.5) due to Döderlein's lactobacilli.
Endometrium
Example
Hyperplasia of endometrium from unopposed oestrogen (no progesterone) increases endometrial cancer risk.
Inner mucosal lining of the uterus; site of implantation, menstrual shedding, and response to cyclic hormones.
Myometrium
Example
Uterine atony (failure of myometrium to contract postpartum) causes severe postpartum haemorrhage (PPH).
Thick smooth muscle layer of the uterus; contracts during labour and compresses spiral arteries to arrest postpartum bleeding.
Fimbriae
Example
Scarring from PID can damage fimbriae, causing tubal infertility and ectopic pregnancy risk.
Finger-like projections on the distal end of fallopian tube that sweep the ovum into the tube after ovulation.
Ampulla
Example
Fertilisation occurs in the ampulla; if the blastocyst implants in the tube (ectopic pregnancy), it will rupture and haemorrhage.
Widest, most muscular portion of the fallopian tube (outer third); normal site of fertilisation.
Ovary
Example
A female is born with ~1–2 million oocytes, declining to ~400,000 at puberty; only ~400 will ovulate in a lifetime.
Paired gonad producing oocytes (eggs) and secreting oestrogen and progesterone; no new oocytes are produced after birth.
Cervix
Example
Cervical incompetence (premature dilation) increases miscarriage risk, especially in 2nd trimester; treated with cervical cerclage.
Lower portion of uterus extending into vagina; opens slightly during cycle and dilates to 10 cm during labour.
Perineum
Example
A 3rd-degree perineal tear extends into the external anal sphincter; careful repair is needed to prevent faecal incontinence.
Area between vaginal opening and anus; site of episiotomy or spontaneous lacerations during vaginal delivery.
Diagrams to know
- Sagittal cross-section of female pelvis showing uterus, fallopian tubes, ovaries, vagina, bladder, rectum, and perineum.
- Coronal view of uterus and fallopian tubes showing fundus, corpus, cervix, fimbriae, ampulla, isthmus.
- Cross-section of ovary showing primordial follicle, primary follicle, secondary follicle, mature (Graafian) follicle, corpus luteum.
- Superior view of female pelvis showing gynaecoid, android, platypelloid, and anthropoid pelvic shapes; measurements of pelvic diameters.
Reproductive Hormones & Their Actions
Common values
Value
24–36 hours before ovulation
Symbol
t_LH_surge
Quantity
LH surge duration
Value
~200 pg/mL (17β-oestradiol)
Symbol
[E2]_threshold
Quantity
Oestrogen threshold for LH surge
Value
~14 days (fixed, unless rescued by hCG)
Symbol
t_CL
Quantity
Corpus luteum lifespan
Value
~0.3–0.5°C
Symbol
ΔT_BBT
Quantity
BBT rise after ovulation
Important facts
- GnRH is released in pulses (not continuously) to maintain sensitivity of pituitary; constant exposure downregulates receptors.
- FSH rises early in follicular phase to recruit follicles; only the follicle with most FSH receptors (highest local oestrogen) survives to become dominant follicle.
- LH surge occurs when oestrogen reaches a threshold (~200 pg/mL); surge lasts 24–36 hours and triggers ovulation.
- Oestrogen exerts negative feedback on FSH when low, preventing multiple follicles; positive feedback on LH surge when high (triggering ovulation).
- Progesterone exerts negative feedback on FSH/LH; prevents follicle recruitment and protects early pregnancy by thickening cervical mucus.
- After ovulation, corpus luteum secretes progesterone for ~14 days; if no pregnancy, corpus luteum regresses to corpus albicans.
- hCG maintains corpus luteum when β-hCG levels >10 mIU/mL; without hCG, corpus luteum regresses and progesterone drops, causing miscarriage.
- Oestrogen alone (without progesterone) causes unopposed proliferation of endometrium, increasing cancer risk; always give progesterone with HRT or oestrogen-only therapy in women with uterus.
- Spinnbarkeit (thin, stretchy cervical mucus) occurs during fertile window due to high oestrogen; thickens under progesterone (post-ovulation) to block sperm entry.
Key definitions
GnRH (gonadotropin-releasing hormone)
Example
GnRH agonists (e.g., leuprolide) suppress FSH/LH by downregulating GnRH receptors; used to suppress endometriosis.
Decapeptide from hypothalamus; released in pulses to stimulate anterior pituitary FSH and LH release.
FSH (follicle-stimulating hormone)
Example
Rising FSH in early follicular phase recruits multiple follicles; only one becomes dominant due to high local oestrogen and FSH receptor expression.
Gonadotropin from anterior pituitary; stimulates ovarian follicle growth and oestrogen production in females; supports spermatogenesis in males.
LH (luteinizing hormone)
Example
LH surge is the trigger for ovulation; ovulation predictor kits detect urinary LH surge to identify the fertile window.
Gonadotropin from anterior pituitary; the sharp LH surge (~24–36 hours before ovulation) triggers rupture of mature follicle and ovulation.
Oestrogen (17β-oestradiol, oestrone, oestriol)
Example
Rising oestrogen in late follicular phase exerts positive feedback on LH, triggering the LH surge and ovulation.
Steroid hormone primarily from granulosa cells of growing follicle; promotes endometrial proliferation, thin cervical mucus (spinnbarkeit), and secondary sex characteristics.
Progesterone
Example
Progesterone withdrawal (corpus luteum regression) triggers menstruation; mifepristone (progesterone antagonist) induces medical abortion.
Steroid hormone from corpus luteum (and later placenta); makes endometrium secretory, thickens cervical mucus, raises BBT by ~0.3–0.5°C, and maintains early pregnancy.
hCG (human chorionic gonadotropin)
Example
hCG is detected by pregnancy tests (serum β-hCG or urine hCG); rises 48–72 hours after positive test if viable pregnancy.
Glycoprotein from trophoblast/placenta after implantation; maintains corpus luteum to continue progesterone production until placenta takes over (~10 weeks).
Testosterone
Example
Exogenous testosterone (anabolic steroid abuse) suppresses endogenous FSH/LH, causing infertility and testicular atrophy.
Androgen from Leydig cells stimulated by LH; drives spermatogenesis and male secondary sex characteristics; small amounts also produced in females (adrenal/ovary).
Diagrams to know
- Hypothalamic–pituitary–ovarian (HPO) axis showing GnRH → FSH/LH → oestrogen/progesterone with positive and negative feedback loops.
- Hormone surge patterns across menstrual cycle: FSH and LH peaks at ovulation, oestrogen rises in follicular phase and again in luteal phase, progesterone rises in luteal phase.
The Menstrual Cycle: Ovarian & Endometrial Phases
Formulas
Cycle length = Follicular phase + Ovulation + Luteal phase
Meaning
Total cycle duration; average 28 days (range 21–35 days)
Watch out
The follicular phase VARIES (21–35 days); the luteal phase is FIXED at ~14 days. Cycle variation comes from follicular phase length.
When to use
Calculating expected ovulation date or assessing cycle abnormalities
Estimated ovulation date = Cycle length − 14 days
Meaning
Subtract 14 days from cycle length to estimate when ovulation occurred
Watch out
Many students assume ovulation is always day 14; WRONG. Day 14 is only true for 28-day cycles. Use cycle length − 14.
When to use
Predicting ovulation in women with irregular cycles; if cycle is 35 days, ovulation is ~day 21 (not day 14)
Menstrual flow duration = 2–7 days; average blood loss = 30–80 mL
Meaning
Normal parameters for menstruation
Watch out
Patients often overestimate blood loss; teach them that ~1 fully soaked pad = ~5 mL (so 16 pads ≠ 80 mL; 16 pads = ~80 mL).
When to use
Assessing dysmenorrhoea or menorrhagia; losses >80 mL or flow >7 days warrant investigation
Common values
Value
21–35 days (average 28 days)
Symbol
C_len
Quantity
Normal cycle length
Value
Variable, 10–24+ days (average ~14 days)
Symbol
t_foll
Quantity
Follicular phase length
Value
Fixed, ~14 days (range 12–16 days)
Symbol
t_lut
Quantity
Luteal phase length
Value
2–7 days (average ~4–5 days)
Symbol
t_menses
Quantity
Menstrual flow duration
Value
30–80 mL per cycle
Symbol
V_blood
Quantity
Average menstrual blood loss
Value
Days 1–5 (variable)
Symbol
d_mens
Quantity
Days of menstrual flow
Value
Days 6–14
Symbol
d_prol
Quantity
Days of proliferative phase
Value
Days 15–28
Symbol
d_secr
Quantity
Days of secretory phase
Important facts
- Day 1 of cycle = first day of menstrual bleeding (not first day of spotting or last day of prior cycle).
- Follicular phase length varies (21–35+ days depending on cycle length); luteal phase is FIXED at ~14 days.
- In a 28-day cycle: follicular phase ~14 days, luteal phase ~14 days. In a 35-day cycle: follicular phase ~21 days, luteal phase ~14 days.
- LH surge occurs ~24–36 hours before ovulation; is the most reliable predictor of imminent ovulation.
- Ovulation is a SINGLE event (release of one secondary oocyte from one ovary, usually alternating); does not occur twice in one cycle.
- After ovulation, ovum has ~24 hours of viability in fallopian tube; fertilisation must occur within this window.
- Corpus luteum is maintained by LH in non-pregnant cycle and by hCG in pregnancy; both bind the same luteal LH receptor.
- Progesterone withdrawal (not absolute progesterone level) triggers menstruation; as long as progesterone remains high, menses is prevented.
- Cervical mucus viscosity is regulated solely by oestrogen (thin at ovulation) and progesterone (thick post-ovulation); NOT by FSH/LH.
- Normal cycle variability is ±5 days around 28-day average; >35 days = oligomenorrhoea, <21 days = polymenorrhoea.
- Implantation occurs ~6–10 days after fertilisation (days 20–24 of a 28-day cycle); hCG becomes detectable 7–12 days post-ovulation.
Key definitions
Follicular phase (ovarian cycle)
Example
In a 35-day cycle, follicular phase lasts ~21 days (35 − 14); in a 21-day cycle, only ~7 days.
Days 1–13 (variable length) of cycle; FSH recruits and stimulates growth of ovarian follicles; dominant follicle emerges and secretes rising oestrogen.
Ovulation
Example
LH surge detected on day 13 morning → ovulation likely occurs day 14 afternoon. Ovulation predictor kits detect LH surge to time intercourse.
Day ~14 of a 28-day cycle (varies with cycle length); LH surge ruptures mature follicle, releasing secondary oocyte; occurs ~24–36 hours after LH surge onset.
Luteal phase (ovarian cycle)
Example
The luteal phase length is predictable; if cycle is 28 days, luteal phase is day 15–28 (~14 days); if 35 days, luteal phase is still ~14 days.
Days 15–28; remarkably constant at ~14 days (range 12–16 days); ruptured follicle becomes corpus luteum, secreting progesterone; if no pregnancy, corpus luteum regresses.
Menstrual phase (endometrial cycle)
Example
Menstruation is triggered by progesterone withdrawal, not absolute hormone levels; if progesterone remains high, menses will not occur (basis for progesterone-only contraceptives).
Days 1–5 of cycle; functional layer of endometrium sheds due to falling oestrogen and progesterone (corpus luteum regression).
Proliferative phase (endometrial cycle)
Example
Rising oestrogen promotes endometrial growth; endometrium thickens from ~2 mm (menstrual) to ~8–12 mm (ovulation).
Days 6–14; oestrogen-driven endometrial thickening and gland proliferation; ends at ovulation; also called follicular phase endometrially.
Secretory phase (endometrial cycle)
Example
Endometrial glands become coiled ("corkscrew"), tortuous, and filled with glycogen and mucus; endometrial thickness remains ~8–12 mm.
Days 15–28; progesterone-driven transformation of endometrium into secretory, nutrient-rich tissue ready for implantation; also called luteal phase endometrially.
Spinnbarkeit
Example
Cervical mucus transitions from thick (post-menstrual) → increased volume (proliferative) → peak spinnbarkeit (ovulation) → thick/reduced (secretory).
Clear, thin, stretchy (raw egg white–like) cervical mucus during fertile window; indicates high oestrogen and peak fertility.
Mittelschmerz
Example
Some women use mittelschmerz as a sign of ovulation, though pain is not reliable for contraception (occurs in only ~20% of cycles).
Mid-cycle pelvic pain or cramping experienced by ~20% of women at or near ovulation; unilateral (side of ovulating ovary).
Basal body temperature (BBT)
Example
BBT rise is RETROSPECTIVE proof of ovulation (not predictive); used to confirm ovulation has occurred after the fact.
Body temperature measured immediately upon waking; dips slightly before ovulation, then rises ~0.3–0.5°C after ovulation due to progesterone; remains elevated until menses.
Corpus luteum
Example
If pregnancy occurs, hCG from trophoblast rescues corpus luteum, preventing regression; if no pregnancy, corpus luteum regresses to corpus albicans (white scar).
Endocrine structure formed from granulosa and theca cells of ruptured follicle; secretes progesterone and small amounts of oestrogen for ~14 days.
Dominant follicle
Example
Multiple follicles are recruited, but only one becomes dominant (days 5–7); selection is driven by positive feedback of its own oestrogen on FSH receptors.
Single follicle (usually) that continues to grow and mature while others regress; has highest FSH receptor expression and produces peak oestrogen.
Diagrams to know
- Complete menstrual cycle diagram showing ovarian cycle (follicular, ovulation, luteal) and endometrial cycle (menstrual, proliferative, secretory) in parallel, with FSH/LH surge, oestrogen/progesterone levels, endometrial thickness, and cervical mucus changes.
- BBT curve showing dip before ovulation and sustained rise post-ovulation (0.3–0.5°C above baseline) until menses.
- Cervical mucus progression: thick (menstrual) → creamy (early follicular) → stretchy/clear/abundant (ovulatory) → thick/scanty (luteal).
Fertility, Conception & Early Pregnancy
Formulas
Fertile window ≈ 5 days before ovulation through 1 day after ovulation
Meaning
Period when unprotected intercourse can result in pregnancy
Watch out
The fertile window is NOT fixed to days 12–16 of a 28-day cycle; it depends on when ovulation actually occurs in that individual.
When to use
Counselling couples planning or avoiding pregnancy; basis for fertility awareness method (FAM) and natural family planning
Ovum viability = ~24 hours after ovulation
Meaning
Duration ovum remains capable of fertilisation in fallopian tube
Watch out
Sperm are the primary determinant of fertile window length, not ovum; an ovum can be fertilised for ~24 hours, but sperm can wait 5 days.
When to use
Explaining why timing of intercourse matters; sperm survival is much longer (48–72 hours)
Sperm viability in female tract = 48–72 hours (up to 5 days in fertile cervical mucus)
Meaning
Sperm can remain motile and capable of fertilisation for this period
Watch out
Many contraceptive failures occur because couples underestimate sperm survival time (assume 24 hours); sperm can survive 5 days.
When to use
Explaining pregnancy risk during days 1–5 of cycle or from intercourse 3–5 days before ovulation
Implantation timing = 6–10 days post-fertilisation (days 20–24 of 28-day cycle)
Meaning
Time from fertilisation to blastocyst embedding in endometrium
Watch out
hCG is not detectable until implantation (days 6–10 post-fertilisation); early pregnancy tests may be falsely negative before implantation.
When to use
Predicting when hCG becomes detectable (7–12 days post-ovulation); timing of pregnancy symptoms
hCG detection = 7–12 days post-ovulation (or 1–5 days post-implantation)
Meaning
Time when hCG reaches detectable levels in blood or urine
Watch out
hCG doubles every 48–72 hours in early pregnancy; a single hCG level is less informative than serial measurements.
When to use
Counselling on when to test for pregnancy; explaining false-negative early pregnancy tests
Common values
Value
~5 days before ovulation + 1 day after = ~6 days total
Symbol
t_fertile
Quantity
Fertile window length
Value
~24 hours after ovulation
Symbol
t_ovum_viable
Quantity
Ovum viability
Value
48–72 hours (up to 5 days in fertile mucus)
Symbol
t_sperm_viable
Quantity
Sperm viability in female tract
Value
Days 0–4 post-fertilisation
Symbol
t_cleavage
Quantity
Cleavage (zygote → morula)
Value
Days 4–5 post-fertilisation
Symbol
t_blastocyst
Quantity
Blastocyst formation
Value
Days 6–10 post-fertilisation (average day 8)
Symbol
t_implant
Quantity
Implantation timing
Value
48–72 hours in early pregnancy
Symbol
t_hCG_double
Quantity
hCG doubling time
Value
35 years (advanced), 40 years (very advanced)
Symbol
Age_maternal
Quantity
Minimum female age for advanced maternal age
Important facts
- Cleavage produces daughter cells that are smaller than parent cell (true cell division, not just reduction).
- Morula stage occurs days 3–4; blastocyst forms by day 4–5 post-fertilisation.
- Blastocyst hatches from zona pellucida before implantation; zona pellucida prevents polyspermy and embryo fragmentation.
- Implantation is a two-way process: trophoblast invades endometrium ("trophoblastic invasion") AND endometrium accepts blastocyst ("receptivity"); both must align.
- After implantation, trophoblast secretes hCG to maintain corpus luteum; hCG is detectable in blood serum by ~8–10 days post-ovulation.
- Maternal age is the single strongest predictor of fecundity; oocyte quality (not quantity) declines with age, increasing risk of aneuploidy (Down syndrome).
- Ovum viability is the limiting factor for timing intercourse; since ovum only lasts ~24 hours, intercourse before ovulation (when sperm can wait 5 days) is more effective.
- Male factor infertility (~30%) is primarily low sperm count (<15 million/mL), poor motility (<40% motile), or poor morphology (<4% normal).
- Female factor infertility (~35%) includes anovulation (no ovulation), tubal blockage, endometriosis, and poor endometrial receptivity.
- Combined/unexplained infertility (~35%) includes immunological, genetic, and unexplained causes; requires advanced testing and ART.
- Conception most likely if intercourse occurs 1–2 days before ovulation (sperm present in fallopian tube waiting for ovum).
- Chemical pregnancy = positive pregnancy test with no clinical pregnancy (implantation occurs but blastocyst dies before hCG surge).
Key definitions
Fertilisation
Example
If sperm carries X chromosome, female offspring (46,XX); if Y chromosome, male offspring (46,XY).
Fusion of sperm nucleus (23 chromosomes) with secondary oocyte nucleus (23 chromosomes) to form zygote (46 chromosomes); occurs in ampulla of fallopian tube.
Zygote
Example
Zygote undergoes cleavage (mitotic divisions without growth) to form morula (8–16 cells), then blastocyst (fluid-filled, ~100 cells).
Diploid cell (46 chromosomes) formed immediately after fertilisation; first cell of new organism.
Morula
Example
Morula resembles a mulberry (morula = "little mulberry" in Latin); no growth in cell size, only division.
Stage of early embryo (3 days post-fertilisation) consisting of ~8–16 cells in solid mass; results from cleavage of zygote.
Blastocyst
Example
Blastocyst "hatches" from zona pellucida before implantation; trophoblast secretes hCG to maintain corpus luteum.
Stage of early embryo (~4–5 days post-fertilisation) with ~100 cells; contains inner cell mass (ICM, future embryo) and trophoblast (future placenta); capable of implantation.
Implantation
Example
Implantation is NOT complete until ~12 days post-fertilisation; early chemical pregnancy loss can occur before implantation is complete.
Embedding of blastocyst into endometrium; begins ~6–10 days post-fertilisation; trophoblast invades endometrium and forms placental villi.
Ampulla
Example
If fertilisation occurs in isthmus (inner two-thirds), embryo is more likely to implant in tube (ectopic pregnancy); ampulla allows time for blastocyst development.
Widest, outer third of fallopian tube; site of fertilisation; has highest concentration of motile sperm due to peristalsis.
Infertility
Example
Primary infertility = never conceived; secondary infertility = prior pregnancy but now unable to conceive.
Failure to conceive after 12 months of regular unprotected intercourse (or 6 months if female age >35 years).
Fecundity
Example
Female fecundity at age 25 is ~25% per cycle; at age 40 it is ~10% per cycle; at age 45 it is ~3% per cycle.
Biological capacity to conceive and carry pregnancy to term; declines with advancing maternal age, especially after age 35.
Ectopic pregnancy
Example
Risk factors include PID (scarring of tubes), previous ectopic pregnancy, IUD use, assisted reproductive technology (ART).
Implantation outside the uterus, most commonly in fallopian tube (99%); non-viable and life-threatening if ruptures.
Diagrams to know
- Timeline of early pregnancy: day 0 (fertilisation in ampulla) → day 3 (morula, in fallopian tube) → day 4–5 (blastocyst, entering uterus) → day 6–10 (implantation, hCG secretion).
- Fertile window diagram showing 5-day pre-ovulation window (sperm waiting) and 1-day post-ovulation window (ovum viable).
- Graph of hCG concentration over time: undetectable until implantation (~day 6–10 post-ovulation), then rises exponentially, doubling every 48–72 hours.
Menstrual Abnormalities & Terminology
Common values
Value
12–13 years (range 9–16 years)
Symbol
Age_menarche
Quantity
Normal menarche age
Value
No menses by age 15 years or 3 years post-breast development
Symbol
Age_prim_amen
Quantity
Primary amenorrhoea threshold
Value
Absence of menses for ≥3 months in prior menstruating woman
Symbol
t_sec_amen
Quantity
Secondary amenorrhoea definition
Value
>80 mL blood loss per cycle or >7 days duration
Symbol
Menorr_volume
Quantity
Menorrhagia threshold
Value
Cycle >35 days but <3 months
Symbol
t_oligomen
Quantity
Oligomenorrhoea definition
Value
Cycle <21 days
Symbol
t_polygen
Quantity
Polymenorrhoea definition
Value
12 consecutive months without menses
Symbol
t_menopause
Quantity
Menopause definition
Value
51 years (range 40–60 years)
Symbol
Age_menopause
Quantity
Average menopause age
Value
Menopause before age 40 years
Symbol
Age_prem_meno
Quantity
Premature menopause threshold
Important facts
- Primary dysmenorrhoea affects ~50–60% of menstruating women; begins 1–2 years after menarche (when ovulatory cycles begin).
- NSAIDs (mefenamic acid 500 mg TID, ibuprofen 400–600 mg TID with food) are first-line for primary dysmenorrhoea; work by inhibiting PGF2α.
- Secondary dysmenorrhoea suggests underlying pathology (endometriosis, adenomyosis, fibroids); requires imaging and sometimes laparoscopy.
- Menorrhagia increases risk of iron-deficiency anaemia; assess ferritin and Hb; may require iron supplementation.
- Postmenopausal bleeding is NEVER normal; requires pelvic ultrasound to assess endometrial thickness and exclude malignancy.
- Perimenopause is the only time in a woman's life (except during hormonal contraceptive use) when cycles are naturally irregular; contraceptive needs often change.
- Hot flushes in perimenopause are caused by declining oestrogen; managed with hormone replacement therapy (HRT) or non-hormonal alternatives (SSRIs, SNRIs).
- Amenorrhoea >3 months requires investigation; key causes are pregnancy (most common), thyroid disease, hyperprolactinaemia, PCOS, and weight loss.
- Functional hypothalamic amenorrhoea (FHA) from stress, excessive exercise, or weight loss is reversible with lifestyle modification.
- In secondary amenorrhoea, perform pregnancy test FIRST (even if patient denies intercourse) before further workup.
- Oligomenorrhoea is associated with lower fertility but does not indicate anovulation; can still conceive with oligomenorrhoea (cycles are just farther apart).
Key definitions
Amenorrhoea (primary)
Example
Turner syndrome (45,X), müllerian agenesis, or severe eating disorder can cause primary amenorrhoea.
Absence of menarche (first menses) by age 15 years or 3 years post-breast development; indicates developmental delay.
Amenorrhoea (secondary)
Example
Other causes: hypothalamic dysfunction (stress, weight loss), polycystic ovary syndrome (PCOS), thyroid disease, hyperprolactinaemia.
Cessation of menses for ≥3 months in a woman with prior normal menstruation; pregnancy is the most common cause.
Dysmenorrhoea (primary)
Example
Cramping pain in lower abdomen, relieved by NSAIDs (mefenamic acid 500 mg, ibuprofen 400–600 mg) taken with food.
Painful menses with no identifiable pelvic pathology; caused by excess prostaglandin F2α (PGF2α) in endometrium; appears 1–2 years after menarche.
Dysmenorrhoea (secondary)
Example
Deep infiltrating endometriosis or adenomyosis causes progressive dysmenorrhoea; requires imaging (ultrasound, MRI) and sometimes diagnostic laparoscopy.
Painful menses secondary to pelvic pathology such as endometriosis, fibroids, adenomyosis, or PID; often begins in 20s–30s.
Menorrhagia
Example
Causes include fibroids, adenomyosis, coagulopathy, and hormone imbalances; treated with NSAIDs, tranexamic acid, or hormonal contraceptives.
Heavy or prolonged menstrual flow (>80 mL total blood loss per cycle or >7 days duration); increases anaemia risk.
Metrorrhagia
Example
Postcoital bleeding raises concern for cervical pathology (polyps, cervicitis, cancer); postmenopausal bleeding requires endometrial evaluation.
Irregular uterine bleeding between periods (intermenstrual bleeding); suggests structural lesion, infection, or hormone imbalance.
Oligomenorrhoea
Example
PCOS, thyroid disease, or extreme athletic training can cause oligomenorrhoea.
Infrequent, light menstrual periods; cycle >35 days but <3 months apart.
Polymenorrhoea
Example
Short follicular phase (rare) or inadequate luteal phase can cause polymenorrhoea; associated with decreased fertility.
Abnormally frequent menstrual periods; cycle <21 days.
Menopause
Example
Premature menopause (<age 40) is associated with Turner syndrome, fragile X, or autoimmune ovarian failure.
Permanent cessation of menstruation; diagnosed retrospectively after 12 consecutive months without menses; average age ~51 years.
Perimenopause (climacteric)
Example
Cycle irregularity in perimenopause is normal; however, heavy bleeding or postmenopausal bleeding warrants evaluation.
Transitional years (usually 5–10 years) before menopause; marked by irregular cycles, declining oestrogen, and vasomotor symptoms (hot flushes, night sweats).
Mittelschmerz
Example
Mittelschmerz can help identify ovulation but is not reliable for contraception; some women have it every cycle, others rarely.
Mid-cycle pelvic pain or cramping at or near ovulation (day ~14); occurs in ~20% of ovulatory cycles; unilateral (side of ovulating ovary).
Spinnbarkeit
Example
Peak spinnbarkeit occurs 1–2 days before ovulation and is a sign of peak fertility; mucus viscosity changes are oestrogen-driven.
Clear, thin, stretchy cervical mucus with egg-white consistency during fertile window; stretches >6 cm between thumb and forefinger.
Diagrams to know
- Diagnostic algorithm for secondary amenorrhoea: pregnancy test → TSH, prolactin → LH/FSH → pelvic ultrasound.
- Classification of menstrual abnormalities by frequency (oligomenorrhoea, normal, polymenorrhoea) and flow (hypomenorrhoea, normal, menorrhagia).
Nursing Considerations & Clinical Implications
Important facts
- Teaching about normal menstruation empowers women to recognize abnormalities early and seek care; reduces unnecessary worry about variation.
- Douching disrupts vaginal flora (Döderlein's lactobacilli), increases risk of BV and PID, and may increase ectopic pregnancy risk; counsel women NOT to douche.
- Tampons should be changed every 4–6 hours to reduce risk of toxic shock syndrome (TSS); pads offer alternative with lower TSS risk.
- Heat (heating pad, warm bath) and NSAIDs are first-line non-pharmacological and pharmacological treatment for primary dysmenorrhoea.
- Reassure women that some cycle variation (21–35 days) is normal and does NOT indicate infertility or pathology.
- Counsel couples that timing of intercourse matters: intercourse on days 12–14 of a 28-day cycle (or 3–5 days before expected ovulation) maximizes conception probability.
- Myth: A woman cannot conceive during her period. REALITY: If cycle is short (21–24 days) and sperm survive 5 days, ovulation can occur while bleeding is still present; pregnancy risk is real.
- Myth: Ovulation is always day 14. REALITY: Day 14 is only true for exactly 28-day cycles; estimate ovulation as cycle length minus 14 days.
- If couple has not conceived after 12 months of regular intercourse (or 6 months if female >35 years), refer for infertility workup (semen analysis, ovulation studies, tubal patency tests).
- In Philippine healthcare context (per RA 9173), nurses provide family planning counselling, teach fertility awareness, and refer for specialist care when needed; family planning services are part of reproductive health care delivery.
Key definitions
Perineal hygiene
Example
Teach women to wipe front-to-back after voiding/defecation; back-to-front wiping introduces rectal flora (E. coli) toward urethra.
Proper vulva and perineal cleansing (front-to-back only) to maintain acidic vaginal pH and prevent UTI/reproductive infection.
Fertility awareness method (FAM)
Example
Women track mucus changes (spinnbarkeit peak), BBT rise, and cycle length to avoid or achieve pregnancy; requires education and daily monitoring.
Natural family planning using cervical mucus, BBT, and calendar methods to identify fertile and infertile days; non-hormonal contraception.
Timed intercourse
Example
Couples planning pregnancy are advised to have intercourse every 2–3 days or specifically on days 12–14 of a 28-day cycle (or adjusted for that couple's cycle length).
Intentional intercourse during fertile window to maximize conception probability; basis for fertility counselling and natural conception attempts.
Diagrams to know
- Fertility window prediction: mark cycle length − 14 to estimate ovulation date; explain 5-day pre-ovulation and 1-day post-ovulation windows.
- Teaching aid: normal menstrual cycle phases with symbols for optimal intercourse timing for conception.
Must remember
- FERTILISATION SITE: Fertilisation occurs in the AMPULLA (outer third of fallopian tube), NOT in the uterus. If implantation occurs in the tube, it is an ectopic pregnancy.
- LH SURGE TRIGGERS OVULATION: The sharp LH surge (not FSH) ruptures the mature follicle and triggers ovulation about 24–36 hours later. Ovulation is the release of a secondary oocyte (not a primary oocyte), not a sperm.
- LUTEAL PHASE IS FIXED: The luteal phase is remarkably constant at ~14 days (range 12–16 days). Cycle length variation comes from the follicular phase. Estimate ovulation as CYCLE LENGTH MINUS 14 DAYS (not always day 14).
- SPERM SURVIVAL IS LONG: Sperm survive 48–72 hours routinely and up to 5 days in fertile cervical mucus. Ovum survives ~24 hours. The fertile window is ~5 days BEFORE through 1 day AFTER ovulation because of long sperm survival.
- BBT RISES AFTER OVULATION: Progesterone raises basal body temperature by ~0.3–0.5°C after ovulation; this rise is RETROSPECTIVE proof of ovulation, not predictive. Oestrogen makes cervical mucus thin and stretchy (spinnbarkeit) BEFORE ovulation.
- hCG MAINTAINS CORPUS LUTEUM: Human chorionic gonadotropin (hCG) from the trophoblast/placenta after implantation maintains the corpus luteum, which continues to secrete progesterone. Without hCG, corpus luteum regresses and progesterone drops, causing miscarriage.
- FATHER DETERMINES FETAL SEX: Each sperm carries EITHER an X or Y chromosome. The father's sperm (X or Y) determines whether the offspring is female (46,XX) or male (46,XY). The mother always contributes an X.
- IMPLANTATION TIMING: Implantation occurs 6–10 days after fertilisation (days 20–24 of a 28-day cycle). hCG is first detectable 7–12 days post-ovulation. Early pregnancy tests may be falsely negative before implantation is complete.
- OESTROGEN IS BIPHASIC: Oestrogen rises in the follicular phase (positive feedback triggering LH surge and ovulation), then FALLS, then rises again slightly in the luteal phase (from corpus luteum). Progesterone is primarily luteal (high after ovulation).
- SECONDARY DYSMENORRHOEA NEEDS EVALUATION: Primary dysmenorrhoea (no pathology, from prostaglandins) is treated with NSAIDs. Secondary dysmenorrhoea (from endometriosis, adenomyosis, fibroids, PID) requires imaging and specialist evaluation. Always ask when dysmenorrhoea began.
Last minute tips
- ALWAYS ESTIMATE OVULATION CORRECTLY: Instead of assuming ovulation is day 14, use CYCLE LENGTH MINUS 14. If a woman has a 35-day cycle, ovulation is ~day 21 (35 − 14), not day 14. This is a frequent NLE trick question.
- PREGNANCY TEST IS YOUR FIRST STEP: In any patient with secondary amenorrhoea, ALWAYS perform a pregnancy test FIRST, even if the patient denies intercourse or is using contraception. Pregnancy is the most common cause and must be ruled out before further workup.
- KNOW THE MENSTRUAL CYCLE TERMINOLOGY: Distinguish between oligomenorrhoea (infrequent, >35 days), polymenorrhoea (frequent, <21 days), menorrhagia (heavy/prolonged), metrorrhagia (intermenstrual bleeding), dysmenorrhoea (painful), and amenorrhoea (absent). NLE loves testing terminology.
- SPINNBARKEIT & BBT ARE NOT TIMING TOOLS: Spinnbarkeit (thin, stretchy mucus) appears 1–2 days BEFORE ovulation (predictive, good for timing intercourse). BBT rise occurs AFTER ovulation (retrospective proof only, not for predicting ovulation). Know the difference.
- REMEMBER THE FERTILE WINDOW DRIVER: The fertile window is primarily determined by SPERM SURVIVAL (48–72 hours, up to 5 days), not ovum survival (only 24 hours). This is why intercourse 3–5 days before ovulation (sperm waiting) is effective for conception.
Comparison tables
Ovarian Cycle Phases vs. Endometrial Cycle Phases
| Phase | Ovarian Cycle Name | Days | Key Hormone(s) | Endometrial Phase Name | Endometrial Changes |
|---|---|---|---|---|---|
| Phase 1 | Follicular phase | Days 1–13 (variable) | FSH rising, oestrogen rising | Menstrual phase (days 1–5) + Proliferative phase (days 6–14) | Shedding functional layer → Rebuilding and thickening endometrium |
| Phase 2 | Ovulation | Day ~14 (variable) | LH surge, oestrogen peak | End of proliferative phase | Endometrium reaches peak thickness (~8–12 mm) and vascularity |
| Phase 3 | Luteal phase | Days 15–28 (fixed ~14 days) | Progesterone dominates, oestrogen lower | Secretory phase | Endometrium becomes secretory (coiled glands, glycogen), maintains thickness, prepares for implantation |
Cervical Mucus Changes Throughout Cycle
| Cycle Phase | Days | Mucus Appearance | Mucus Consistency | Spinnbarkeit (Stretch) | Hormone Driver | Fertility Status |
|---|---|---|---|---|---|---|
| Menstrual phase | Days 1–5 | Blood-tinged or absent | Thick, scanty | None or minimal | Progesterone (declining), oestrogen (low) | Infertile |
| Early proliferative | Days 6–10 | Creamy white/yellow | Thick, opaque | Minimal (<2 cm) | Oestrogen (rising) | Low fertility |
| Late proliferative (fertile window) | Days 11–14 | Clear, transparent | Thin, slippery (egg-white) | Maximum (>6 cm, stretchy) | Oestrogen (peak) | HIGH FERTILITY (peak) |
| Ovulation | Day ~14 | Clear, transparent peak | Maximally stretchy | Maximum | Oestrogen peak, LH surge | MAXIMUM FERTILITY (ovulation day ± 1 day) |
| Early luteal | Days 15–20 | Becoming thicker, white | Thicker, curdled | Decreasing | Progesterone (rising) | Declining fertility |
| Late luteal | Days 21–28 | Thick, scanty, opaque | Thick, sticky, minimal | None | Progesterone (high), oestrogen (low) | Infertile |
Male vs. Female Infertility Causes
| Infertility Category | Frequency | Male Factor | Female Factor |
|---|---|---|---|
| Frequency ~1/3 each | ~30–35% of infertile couples | Low sperm count (<15 million/mL), poor motility (<40% motile), poor morphology (<4% normal) | Anovulation (no ovulation from PCOS, thyroid, hyperprolactinaemia), tubal blockage, endometriosis, poor endometrial receptivity |
| Combined/unexplained | ~30–35% of infertile couples | Immunological (antisperm antibodies), genetic, sexual dysfunction | Immunological, genetic, poor egg quality (age-related), uterine factors |
| Initial workup |
Primary vs. Secondary Dysmenorrhoea
| Feature | Primary Dysmenorrhoea | Secondary Dysmenorrhoea |
|---|---|---|
| Underlying pathology | None (prostaglandin-mediated) | Present (endometriosis, adenomyosis, fibroids, PID, IUD) |
| Age of onset | 1–2 years after menarche (when ovulatory cycles begin) | Later onset (20s–30s) or worsening of prior dysmenorrhoea |
| Pain character | Cramping, lower abdominal pain, radiates to lower back/thighs | Severe, progressive, deeper pelvic pain, may include dyspareunia (painful intercourse) |
| Duration | Usually resolves within 2–3 days of menstruation onset | May persist throughout cycle (adenomyosis) or worsen progressively (endometriosis) |
| First-line treatment | NSAIDs (mefenamic acid 500 mg TID, ibuprofen 400–600 mg TID) + heat | NSAIDs + hormonal contraceptives (suppress ovulation/prostaglandins); may require diagnostic imaging or laparoscopy |
| Response to NSAIDs | Excellent (often 80–90% relief) | Variable; depends on underlying cause |
Primary vs. Secondary Amenorrhoea
| Feature | Primary Amenorrhoea | Secondary Amenorrhoea |
|---|---|---|
| Definition | No menarche (first menses) by age 15 years or 3 years post-breast development | Cessation of menses for ≥3 months in woman with prior normal menstruation |
| Prevalence | ~2–5% of women | ~5–15% of women of reproductive age (varies by population) |
| Most common cause | Constitutional delay, gonadal dysgenesis (Turner syndrome), müllerian agenesis | Pregnancy (most common; rule out first!), hypothalamic dysfunction (stress, weight loss), PCOS |
| Initial investigation | Growth assessment, pubertal development staging, pelvic ultrasound, FSH/LH, karyotype if indicated | Pregnancy test FIRST; then TSH, prolactin, LH/FSH, pelvic ultrasound if pregnancy negative |
| Reversibility | Often permanent (structural anomalies); functional causes may be reversible | Often reversible if cause is functional (stress, weight loss); permanent if gonadal failure or structural |
BBT vs. Cervical Mucus vs. LH Surge (Ovulation Prediction Methods)
| Method | How It Works | Timing | Accuracy | Advantages | Disadvantages |
|---|---|---|---|---|---|
| BBT (basal body temperature) | Measure temperature immediately upon waking; rises ~0.3–0.5°C after ovulation due to progesterone | Rise occurs 1–2 days AFTER ovulation (retrospective) | ~80% when used with calendar method | No cost, simple to perform | RETROSPECTIVE proof only; cannot predict ovulation; requires consistency (wake at same time, record before getting up) |
| Cervical mucus (symptothermal method) | Track mucus consistency; peak spinnbarkeit (clear, stretchy, egg-white) occurs 1–2 days before ovulation | Peak mucus precedes ovulation by 1–2 days (predictive window) | ~80–90% if woman is trained | Predictive of ovulation; can identify fertile window before ovulation | Requires daily self-assessment; learning curve; unreliable if cervicitis, hormonal contraceptives, or abnormal vaginal flora |
| LH surge (ovulation predictor kit) | Detect LH surge in urine using home test kit; surge occurs 24–36 hours before ovulation | Detects surge 1–2 days before ovulation (predictive) | ~99% when used correctly | Most accurate; urine testing is convenient and quick (result in 5 minutes) | Cost (~$10–20 per kit, need multiple per cycle); can miss surge if urine diluted or timing off; relies on regular cycle |
Menstrual Cycle Terminology: Normal vs. Abnormal
| Terminology | Cycle Length / Frequency | Flow Duration | Flow Volume | Category |
|---|---|---|---|---|
| Normal | 21–35 days | 2–7 days | 30–80 mL | NORMAL |
| Oligomenorrhoea | >35 days to <3 months | Variable | Often light | ABNORMAL FREQUENCY (infrequent) |
| Polymenorrhoea | <21 days | Variable | Variable | ABNORMAL FREQUENCY (frequent) |
| Amenorrhoea | Absent ≥3 months | N/A | N/A | ABNORMAL FREQUENCY (absent) |
| Menorrhagia | Normal (21–35 days) | >7 days | >80 mL per cycle | ABNORMAL FLOW (heavy/prolonged) |
| Hypomenorrhoea | Normal (21–35 days) | Shortened (<2 days) | <30 mL per cycle | ABNORMAL FLOW (light/short) |
| Metrorrhagia | Irregular (bleeding between periods) | Irregular | Variable | ABNORMAL PATTERN (intermenstrual bleeding) |
Diagrams
Menstrual Cycle: Hormones, Phases & Ovulation Timeline
This flowchart visualizes the complete menstrual cycle from day 1 through ovulation and either menstruation or pregnancy. It shows the hormonal triggers (FSH, oestrogen, LH surge), the transition between phases, and the key decision point of fertilisation. The flowchart helps students see the sequential nature of the cycle and understand how the luteal phase either leads to menstruation or pregnancy.
Reproductive System: Anatomy & Hormones Overview
This mind map provides a comprehensive overview of the entire reproductive system, hormones, menstrual cycle phases, and conception. It shows how male and female anatomy, hormones, and the menstrual cycle are interconnected and culminate in either menstruation or pregnancy. The hierarchical structure helps students see both the big picture and the specific details.
Ovarian Follicle Development & Corpus Luteum Lifecycle
This state diagram shows the lifecycle of the ovarian follicle from recruitment through ovulation, and the fate of the corpus luteum depending on whether fertilisation and hCG production occurs. It illustrates how corpus luteum regression leads to menstruation, while hCG rescue (pregnancy) maintains progesterone production.
Secondary Amenorrhoea: Diagnostic Approach
This flowchart is a practical diagnostic algorithm for secondary amenorrhoea. It emphasizes that pregnancy testing MUST be the first step, followed by systematic assessment of pituitary (TSH, prolactin), gonadal (LH/FSH), and structural (ultrasound) factors. It helps students organize the differential diagnosis and understand the logical sequence of investigations.
Causes of Infertility (Approximate Distribution)
This pie chart shows the roughly equal distribution of infertility causes among male, female, and combined/unexplained factors. It emphasizes that in any infertile couple, all three categories must be investigated. Male factor is often overlooked but represents about one-third of cases.