Clinical overview
Birth is the most abrupt physiological transition a human ever undergoes. In the space of a few minutes the fetus must convert from an organism whose lungs are fluid-filled and bypassed, whose oxygenation and clearance are entirely placental, and whose circulation runs largely in parallel, into a neonate that ventilates air, oxygenates across its own alveoli, and runs its circulation in series. Most babies accomplish this themselves: roughly 85% breathe spontaneously within 10–30 seconds of birth and a further 10% respond to drying and stimulation, so that only about 5% require any active resuscitation and around 1% need extensive intervention (standard ILCOR/NRP teaching). The registrar's task is to understand the physiology well enough to recognise the small but important minority in whom transition fails, and to support — not interrupt — the majority in whom it succeeds.
The "first few days" of the objective spans three overlapping phases: the immediate cardiorespiratory transition (minutes to hours), consolidation of an air-breathing circulation and metabolic independence over the first 24 hours, and the slower closure of fetal shunts, establishment of feeding, thermal and glycaemic stability, and the early detection of disease over days one to three. Failure at any phase has obstetric relevance because the commonest precipitants — intrapartum hypoxia, prematurity, meconium, maternal sedation, infection, and cold stress — are largely things the labour ward and theatre can either cause or prevent. This chapter sits alongside initiation-of-respiration and neonatal-resuscitation; the emphasis here is the physiology of adaptation and what to watch for as it unfolds.
Core knowledge
The fetal starting point
In utero the lungs are not collapsed but distended with fetal lung fluid actively secreted by the pulmonary epithelium via chloride-driven transport. Pulmonary vascular resistance (PVR) is high — pulmonary arterioles are thick-walled and constricted in the low-oxygen fetal environment — so only a small fraction of combined ventricular output perfuses the lungs. The rest is diverted through two right-to-left shunts: the foramen ovale (right atrium to left atrium) and the ductus arteriosus (pulmonary artery to descending aorta). Oxygenated blood returns from the placenta via the umbilical vein, partly bypassing the liver through the ductus venosus. The result is a parallel circulation tuned to deliver the best-oxygenated blood to the heart and brain.
The respiratory switch
Figure L3.1 — How the newborn moves from placental parallel circulation to air-breathing series circulation: lung liquid clears, PVR falls, SVR rises and fetal shunts functionally close while remaining reactive.
Three events must coincide. First, lung fluid must clear. Labour itself drives a catecholamine and steroid surge that switches the alveolar epithelium from chloride/fluid secretion to sodium absorption through epithelial sodium channels, beginning reabsorption before delivery; the remainder is cleared by the mechanical and transpulmonary pressure changes of the first breaths and by lymphatic and capillary uptake. This is the physiological reason elective caesarean before labour, particularly before 39 weeks, carries a higher rate of transient tachypnoea of the newborn (TTN) — the lung-fluid clearance program has not been triggered.
Second, the first breaths must aerate the lung. The initial inflations generate large negative (and, with crying, positive) transpulmonary pressures — classically of the order of tens of cmH₂O — to overcome surface tension and the viscosity of residual fluid, and to establish a functional residual capacity. Surfactant, produced by type II pneumocytes and present in mature quantity from roughly 34–35 weeks, lowers alveolar surface tension and prevents end-expiratory collapse; its deficiency is the basis of respiratory distress syndrome (RDS) of prematurity and the rationale for antenatal corticosteroids (see preterm-birth-and-pprom).
Third, oxygenation must rise. As the alveoli fill with air, alveolar oxygen tension climbs.
The circulatory switch
Lung aeration is the master switch for the circulation. Alveolar distension and the rise in oxygen tension cause a sharp fall in pulmonary vascular resistance, so pulmonary blood flow increases several-fold. This raises pulmonary venous return and left atrial pressure. Simultaneously, clamping the cord (or the natural cessation of umbilical flow) removes the low-resistance placental bed, raising systemic vascular resistance. Left atrial pressure now exceeds right atrial pressure, functionally closing the foramen ovale. The ductus arteriosus constricts in response to the rising arterial oxygen tension and the fall in circulating placentally-derived prostaglandins; functional closure usually occurs within the first day or two, with anatomical closure over the following weeks. The ductus venosus closes as umbilical flow ceases. The circulation has gone from parallel to series.
Crucially, this is not instantaneous. For the first hours to days the shunt pathways are anatomically patent but functionally closed and remain reactive: hypoxia, acidosis, hypothermia, sepsis or hypoglycaemia can re-constrict the pulmonary vasculature, re-open right-to-left shunting and produce persistent pulmonary hypertension of the newborn (PPHN). This reversibility is why the first days matter and why cold, hypoxia and infection are dangerous — they can drive the circulation backwards.
Cord clamping and the transition
A key insight from the last decade, embedded in ILCOR/ERC newborn guidance, is that establishing ventilation before clamping the cord smooths the transition: aerating the lung drops PVR and lets the left ventricle be preloaded by pulmonary venous return rather than losing its placental preload abruptly. This underpins the recommendation for delayed (deferred) cord clamping — commonly cited as at least 60 seconds in the uncompromised term and preterm infant — which increases neonatal blood volume and iron stores and is associated with better outcomes in preterms. The SA National Integrated Maternal and Perinatal Care Guideline endorses delayed cord clamping for vigorous infants.
Metabolic, thermal and other adaptations
- Glucose: the placental glucose supply stops at birth. The neonate mobilises hepatic glycogen and begins gluconeogenesis and lipolysis; blood glucose dips physiologically in the first 1–2 hours and then recovers with feeding. Infants of diabetic mothers, growth-restricted, preterm and cold-stressed babies are at risk of symptomatic hypoglycaemia.
- Temperature: the wet newborn loses heat rapidly by evaporation, convection, conduction and radiation. Non-shivering thermogenesis via brown adipose tissue (uncoupling protein/UCP-1) is the principal heat source. Cold stress increases oxygen and glucose consumption and can precipitate hypoglycaemia, acidosis and PPHN — hence drying and warmth are the first resuscitation steps.
- Haematology and bilirubin: high-affinity fetal haemoglobin is gradually replaced; the breakdown of a relatively high red-cell mass, combined with immature hepatic conjugation, produces the common physiological jaundice appearing after the first 24 hours.
- Gut and renal: the gut begins to handle enteral feeds and is colonised; meconium passes (usually within 24–48 hours); renal function and fluid handling mature with a normal early diuresis and modest weight loss.
Assessment
The Apgar score
The Apgar score, assigned at 1 and 5 minutes (and repeated every 5 minutes up to 20 if the 5-minute score is below 7), summarises five signs each scored 0–2.
| Sign | 0 | 1 | 2 |
|---|---|---|---|
| Heart rate | Absent | <100/min | ≥100/min |
| Respiratory effort | Absent | Slow, irregular | Good, crying |
| Muscle tone | Limp | Some flexion | Active motion |
| Reflex irritability | None | Grimace | Cry/cough/sneeze |
| Colour | Blue/pale | Body pink, extremities blue | Completely pink |
The Apgar describes the infant's condition and response; it is not a tool for deciding whether to resuscitate (that decision is driven by breathing, tone and heart rate, assessed from the moment of birth) and a single low score does not diagnose intrapartum hypoxia or predict long-term outcome. Heart rate is the single most important sign of effective transition.
The first minutes — ongoing assessment
Resuscitation/transition assessment is a continuous cycle of breathing, heart rate, tone and colour. Heart rate is the key indicator of adequacy of ventilation and is best assessed by auscultation or, more reliably, ECG/pulse oximetry. Pre-ductal SpO₂ (right hand/wrist) is interpreted against the accepted gradual rise — it is normal for a healthy term baby to take roughly 5–10 minutes to reach saturations in the high 80s to low 90s, so do not over-oxygenate a pink, vigorous baby chasing an adult target. Central cyanosis persisting beyond the first several minutes, or pallor, is abnormal.
Routine newborn care and examination
- Immediate: dry, stimulate, assess; skin-to-skin with the mother for the well term baby; delayed cord clamping; keep warm; early breastfeeding (see infant-feeding).
- A structured newborn examination within the first 24 hours and again before discharge: tone and posture, colour, respiratory rate and work of breathing, heart sounds and femoral pulses, the red reflex, palate, hips (developmental dysplasia), spine, anus and genitalia.
- Identify risk: gestation and growth, maternal HIV and other infections, intrapartum events, meconium, prematurity.
Monitoring over the first days
Figure L3.2 — First-72-hours transition dashboard: Apgar documentation, gradual preductal saturation rise, thermoglycaemic adaptation, jaundice timing and the settled-then-sick red flags.
Watch the trajectory: feeding and urine/stool output, weight (modest loss is normal), temperature stability, jaundice (timing matters — see Red flags), tone and activity, and respiratory pattern. A baby who was transitioning well and then deteriorates is the one to fear — late deterioration suggests sepsis, a duct-dependent cardiac lesion, or a metabolic problem.
South African context
In South Africa most births are facility-based but staffing and equipment vary widely across district, regional and tertiary levels (see sa-maternity-guidelines). Practical implications: every delivery point must have a functioning resuscitaire, warmth, suction and a self-inflating bag-valve-mask, and a person competent in newborn resuscitation present at every birth. Helping Babies Breathe (HBB), with its "Golden Minute" to establish ventilation, is the widely-taught low-resource framework and complements ILCOR/NRP. HIV is central: with antenatal ART the great majority of exposed infants are uninfected, but infant prophylaxis and feeding decisions follow the SA Prevention of Vertical Transmission (PVT) programme in the 2026 National Consolidated Guidelines — all HIV-exposed infants now get dual NVP + AZT from birth until the delivery VL is known (see hiv-in-pregnancy). Hypothermia and hypoglycaemia are common, preventable killers in transport and after home or before-arrival births — "warm chain" and early feeding are emphasised.
Management
Supporting normal transition
For the vigorous term baby the "management" is mostly not interfering: dry and place skin-to-skin, keep warm, defer cord clamping in the uncompromised infant, and support early breastfeeding. Routine deep suctioning of a vigorous baby is not recommended and can cause reflex bradycardia. Vitamin K and eye/other prophylaxis are given per local protocol.
When transition fails — the resuscitation drill
Figure L3.3 — Failed-transition ladder: support normal adaptation, prioritise effective ventilation, escalate to 3:1 compressions only after chest-moving ventilation, and screen common early problems.
NEONATAL RESUSCITATION — immediate drill (ILCOR/ERC/NRP-aligned). Call for help. Start the clock. Dry, stimulate, keep warm.
- Airway/position: neutral ("sniffing") position; clear the airway only if obstructed.
- Breathing: if not breathing or gasping, or heart rate <100/min after stimulation → give five inflation breaths with a mask, starting with air in the term baby and titrating oxygen to pre-ductal SpO₂. Confirm chest movement.
- Reassess heart rate. If it rises, the lung has aerated — continue ventilation until spontaneous breathing.
- If heart rate stays <60/min despite 30 seconds of effective (chest-moving) ventilation → start chest compressions at 3:1 with ventilation and increase the oxygen.
- Recheck every ~30 seconds. If still <60/min with effective ventilation and compressions → adrenaline (preferably via an umbilical venous catheter) and consider volume; correct hypoglycaemia and hypothermia; consider a pneumothorax. The single most effective intervention is effective ventilation — most newborns who need help need their lungs aerated, not drugs. For the full algorithm see neonatal-resuscitation.
Specific early problems and their management
- TTN: tachypnoea from delayed lung-fluid clearance, commonest after pre-labour caesarean; supportive oxygen, usually self-limiting over 24–72 hours — but it is a diagnosis of exclusion (rule out sepsis and pneumonia).
- RDS (surfactant deficiency, preterm): antenatal corticosteroids are the key obstetric preventive (RCOG GTG 74); postnatally, CPAP/respiratory support and exogenous surfactant where indicated. Anticipate it at the preterm delivery.
- Meconium-stained liquor: a non-vigorous baby through meconium needs effective ventilation; routine intrapartum suctioning on the perineum and routine tracheal suctioning of the vigorous baby are no longer recommended. Watch for meconium aspiration syndrome and PPHN.
- Hypoglycaemia: feed early; treat symptomatic or persistently low glucose per protocol (enteral feed, and IV dextrose for symptomatic/severe cases). Screen the at-risk (IDM, SGA, preterm, cold).
- Hypothermia: prevent it (warm chain); rewarm carefully if it occurs; remember it drives hypoglycaemia, acidosis and pulmonary vasoconstriction.
- Suspected sepsis: SA has a high burden of early-onset sepsis and group B streptococcus is relevant (RCOG GTG 36). A baby who transitioned then deteriorates, with temperature instability, poor feeding, lethargy or respiratory distress, needs sepsis screen and empirical antibiotics — do not wait.
- Hypoxic-ischaemic encephalopathy (HIE): where there is evidence of significant intrapartum hypoxia with an abnormal neurological state, therapeutic hypothermia (cooling) within the first 6 hours improves outcome and should be arranged/referred where available; this links directly to intrapartum oxygenation and contractions-fetal-oxygenation.
Red flags / pitfalls
- Chasing adult SpO₂ targets in the first minutes. Healthy babies are blue at birth and saturate gradually over ~5–10 minutes; over-oxygenation is harmful. Use pre-ductal (right-hand) readings against the accepted nomogram.
- Drugs before ventilation. Reaching for adrenaline when the chest is not moving is the classic error. Aeration first, always.
- Jaundice in the first 24 hours is never physiological — it implies haemolysis (e.g. Rhesus/ABO; see rh-isoimmunisation) or sepsis and needs urgent investigation. Physiological jaundice appears after day 1.
- The "settled then sick" baby. Deterioration after an initially good transition signals sepsis, a duct-dependent cardiac lesion (presenting as the ductus closes — cyanosis or shock/absent femorals at day 1–3), or a metabolic disorder. Check femoral pulses, pre/post-ductal saturations and glucose.
- Cold and low sugar are linked and lethal. Hypothermia increases glucose consumption and can re-open pulmonary shunting — a small baby left wet and unwrapped on the resuscitaire is at real risk.
- Maternal opioids/sedation or magnesium can depress neonatal respiration and tone — anticipate at delivery; support ventilation (naloxone is not a first-line substitute for ventilation and is contraindicated in the baby of an opioid-dependent mother).
- Forgetting the obstetric causes. Most failed transitions trace to something on the labour ward — hypoxia, prematurity, infection, sedation, cold. Prevention upstream beats rescue downstream.
- Deferring cord clamping in a flat baby who needs resuscitation — if effective ventilation cannot be given at the perineum, move to resuscitation rather than rigidly delaying clamping.
Evidence anchors
- ILCOR 2025 Consensus on Science with Treatment Recommendations (CoSTR), ERC 2025 Newborn Life Support, and AAP Neonatal Resuscitation Program (NRP, 8th ed) — delayed cord clamping, dry/warm, inflation breaths, 3:1 compression:ventilation, air-to-titrated-oxygen, the "golden hour"/"Golden Minute".
- Helping Babies Breathe (HBB) — low-resource newborn resuscitation framework relevant to SA district practice.
- South African National Integrated Maternal and Perinatal Care Guideline (NDoH, 2024) — routine newborn care, delayed cord clamping, the warm chain, and resuscitation standards in the SA system.
- National Consolidated Guidelines for the Prevention and Management of HIV… in Pregnant & Breastfeeding Women (NDoH, published January 2026) — supersedes the 2023 ART + 2019 PMTCT guidelines; the Prevention of Vertical Transmission (PVT) programme now gives all HIV-exposed neonates dual prophylaxis (NVP + AZT) from birth until the delivery VL is known and no longer gives them cotrimoxazole (see hiv-in-pregnancy).
- RCOG Green-top Guideline No. 74 — Antenatal Corticosteroids — surfactant maturation and RDS prevention at preterm delivery.
- RCOG Green-top Guideline No. 36 — Group B Streptococcal disease prevention — early-onset neonatal sepsis context.
- Surfactant timing (~34–35 weeks), Apgar scoring, and the proportions of newborns needing help are standard ILCOR/NRP teaching; specific physiological pressures and saturation timings are described cautiously as standard teaching rather than against a single line-itemed source.