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.