Reproduction, preconception, conception and the fetus

Female Anatomy

• Internal genitalia:

  • Ovaries: Produce ova/oocytes (oogenesis), estrogen, and progesterone.

  • Fallopian tubes: Transport oocytes to the uterus, not anatomically connected to ovaries; fimbriae assist ovum movement.

  • Uterus: Fundus, body (implantation site), cervix; uterine positions (anteversion, anteflexion); supported by ligaments.

  • Cervix: Connects uterus to vagina with internal and external os.

  • Uterus Layers: Perimetrium, Myometrium, Endometrium

• External genitalia (Vulva):

  • Mons pubis, labia majora/minora, clitoris, hymen, vestibular bulbs, vestibule.

  • Skene's glands: Lubrication, antimicrobial properties.

  • Bartholin's glands: Mucous secretion for lubrication.

Naegele's Rule

• Estimates the expected date of birth (EDB) by adding 9 months and 7 days to the first day of the last normal menstrual period (LNMP).

• Assumes a 28-day menstrual cycle and conception 14 days after the start of LNMP.

• Adjustments needed for cycles that aren't 28 days.

Male Anatomy

• Testes: Located in the scrotum, produce testosterone and sperm (spermatogenesis).

• Scrotum: Maintains testes temperature lower than 37°C for spermatogenesis.

• Epididymis: Sperm maturation and storage.

• Vas Deferens: Transports sperm from epididymis to ejaculatory duct.

• Urethra: Passage for urine and semen.

• Seminal Vesicles: Secrete fructose and alkaline fluid for sperm.

• Bulbourethral Glands: Secrete alkaline fluid to neutralize vaginal acidity.

• Prostate Gland: Contributes to semen expulsion.

• Penis: Contains corpora cavernosa and corpus spongiosum for erection and semen release.

• Semen: Contains sperm and seminal plasma (nutrients, chemicals for sperm).

Hormones

• Female reproductive cycle controlled by hypothalamic-pituitary-ovarian (HPO) hormones.

• Ovarian cycle phases: Follicular, Ovulatory, Luteal.

• Follicular phase (days 0-13): Follicles mature, producing estrogen, progesterone, and inhibin.

• Ovulatory phase (day 14): Egg release.

• Luteal phase (days 15-28): Corpus luteum forms, producing estrogen, progesterone, and inhibin; degeneration if no fertilization.

• Negative feedback loops regulate hormone levels.

Hormone Summary:

• hCG: Maintains corpus luteum.

• GnRH: Stimulates LH and FSH release.

• FSH: Stimulates maturation of Graafian follicle.

• LH: Triggers ovulation.

• Progesterone: Prepares endometrium, breast development, uterine quiescence.

• Estrogens: Stimulate growth, vascularization, and breast development.

• hPL: Insulin antagonist, colostrum production.

• Oxytocin: Uterine contractions, milk ejection.

• Relaxin: Relaxes pelvic girdle, softens cervix.

• Prolactin: Inhibits ovulation, alveolar development, lactogenesis.

Conception

• Gametes: Sperm and ovum; fertilization occurs in the female reproductive tract.

• Male gametogenesis results in four sperms; female gametogenesis results in one ovum.

• Sperm can survive up to five days before ovulation.

Early Embryogenesis

• Zygote divides by mitosis (cleavage) to form a morula (16-20 cells).

• Morula organizes into a blastocyst (conceptus/pre-embryo).

• Gastrulation: Formation of the trilaminar embryo (ectoderm, mesoderm, endoderm).

Implantation

• Blastocyst implants in the endometrium ~5 days post-fertilization (nidation).

The Embryo

• Cells differentiate into endoderm, mesoderm, and ectoderm.

• Differentiating cells migrate and form rudimentary organs.

Fetal Development and Organogenesis

• Growth: Increase in cell number and size.

• Differentiation: Creation of new cell types.

• Organisation: Coordination of elements into functional units.

• Morphogenesis: Production of specialized cell shapes and structures.

• Occurs cephalo-caudally and from deep to superficial.

Major Fetal Development and Viability

• Viability: Capability of independent existence outside the uterus, typically from 23-24 weeks gestation.

• Survival <24 weeks gestation often associated with neurological impairment.

• Rapid body growth until 24 weeks, followed by slower but constant growth until 30-36 weeks.

• Most susceptible time for congenital defects is during organogenesis (4-10 weeks gestation).

Teratogens

• External agents causing birth defects (drugs, alcohol, infections).

• Exposure timing impacts outcomes.

• Examples: Lithium, warfarin, alcohol, nicotine, TORCH infections, Zika virus.

Fetal Circulation

• Gas exchange occurs in the placenta.

• Fetal hemoglobin has high oxygen affinity.

• Structures: Ductus venosus, foramen ovale, ductus arteriosus, umbilical vein/arteries.

Fetal Circulation Structures:

• Ductus venosus bypasses the liver.

• Foramen ovale shunts blood from right to left atria.

• Ductus arteriosus shunts blood from pulmonary trunk to aortic arch.

• Umbilical vein carries oxygenated blood from placenta.

• Umbilical arteries carry deoxygenated blood to placenta.

Transition to Neonatal Circulation

• Increased systemic vascular resistance.

• Closure of foramen ovale and ductus arteriosus.

• Rapid lowering of pulmonary vascular resistance.

• Essential components: Clearance of lung fluid, surfactant secretion, transition of circulation, endocrine support.

Fetal Skull

• Regions: Face, brow, vertex, occiput.

• Bones: Occipital, parietal, frontal, temporal.

• Sutures: Lambdoid, sagittal, coronal, frontal.

• Fontanelles: Anterior (bregma, diamond-shaped), posterior (lambda, triangular).

• Moulding: Change in fetal head shape during birth due to bone overlap at sutures.