--- module: 025-02 language: en chapter: 25 title: "Reproductive Physiology, Pregnancy, and Lactation" module_title: "Reproductive timing, placental exchange, and adaptation across pregnancy" source_sha256: 9dc43d642a9cf7dfba91f17523d19172a6b86f3f6d811fb7e5c20df7501c205b --- # Reproductive timing, placental exchange, and pregnancy ## Pulsatility and reproductive competence ### Pulsatile releasing hormone sustains gonadotropins ### Continuous exposure desensitises pituitary #### Used therapeutically after initial stimulation ### Energy, stress, sleep, leptin modulate drive ### Functional hypothalamic amenorrhoea #### Gonadotropins and oestradiol fall #### Fertility, bone, cardiovascular effects ### Central precocious puberty: early activation ### Peripheral steroids bypass central drive ### Growth pattern and bone age separate mechanisms ## Follicle selection and luteal physiology ### One follicle becomes dominant ### Two-cell cooperation needs both gonadotropins ### Sustained oestradiol triggers surge ### Progesterone: secretory endometrium, mucus, temperature ### Implantation needs embryo-endometrium synchrony ### Chorionic gonadotropin rescues corpus luteum ### Ovarian reserve is a probability marker #### Not natural fertility or oocyte quality ## Spermatogenesis and androgen regulation ### Sertoli cells form blood-testis barrier ### Intratesticular testosterone far above blood ### Exogenous androgen suppresses gonadotropins #### Reduced sperm, sometimes azoospermia #### Recovery varies with dose and duration ### Semen analysis varies, repeat when appropriate ### Erectile dysfunction can precede vascular disease #### Review medicines and cardiovascular risk ## Placental exchange ### Circulations separate but closely exchanging ### Oxygen transfer depends on content and flow #### Fetal haemoglobin, surface, membrane distance ### Glucose by facilitated transport ### Immunoglobulin G by receptor transport ### Drugs cross by size, charge, lipid, binding ### Not an impermeable shield #### Maternal hypoxaemia or anaemia cuts fetal supply #### Treating the mother often helps the fetus ### Inadequate spiral-artery remodelling #### Placental ischaemia releases factors #### Maternal endothelial dysfunction, hypertension ## Maternal cardiovascular and respiratory reserve ### Output rises, systemic resistance falls #### Unmasks stenosis, pulmonary hypertension ### Supine caval compression, left lateral displacement ### Labour adds autotransfusion and volume shifts #### Complications can emerge after birth ### Progesterone lowers carbon dioxide #### Non-pregnant normal may mean hypoventilation ### Low residual capacity, poor apnoea tolerance ## Renal, haematological, and metabolic adaptation ### Filtration rises early, creatinine and urea fall ### Glycosuria at lower glucose ### Haemodilution with rising iron demand ### Coagulation shifts toward thrombosis ### Insulin resistance can exceed beta-cell reserve #### Gestational diabetes: reassess postpartum ### Drug distribution and clearance change ## Fetal circulation and birth transition ### Umbilical vein carries highest oxygen ### Streaming via foramen ovale to brain ### Right ventricle output bypasses lungs via ductus ### Birth: aeration lowers pulmonary resistance ### Cord separation raises systemic resistance #### Removes placental prostaglandin influence ### Some lesions need an open ductus #### Prostaglandin therapy preserves it ## Labour, haemorrhage, and lactation ### Progress: power, position, pelvis, cervix, time ### Overstimulation can rupture a scarred uterus ### Haemorrhage: tone, tissue, trauma, thrombin #### Trauma bleeds despite a firm uterus #### Coagulation failure worsens all sources ### Placental delivery enables milk secretion ### Stress and pain inhibit ejection reflex ## Reproductive ageing ### Follicle number falls before final menstruation ### Fluctuating oestradiol, one value insufficient ### Faster bone turnover, genitourinary change ### Separate systemic from local symptom needs ## Synthesis across pregnancy care ### State drive, gonads, anatomy, goals, exposures ### Postpartum follow-up beyond bleeding #### Hypertension, thrombosis, mood, thyroid ### Weigh untreated disease against drug risk #### Abrupt withdrawal harms the fetus too ### Labs not judged on non-pregnant ranges alone #### Physiology must not hide pathology