Maternal & Newborn · Topic 58 of 58
Fetal Circulation & Transition at Birth
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Fetal Circulation & Transition at Birth
Before birth the placenta does gas exchange and three shunts route blood past the liver and lungs. At birth the pressures shift and the shunts close; if lung resistance stays high, blood keeps shunting right to left and the newborn stays cyanotic.
Before birth
The placenta, not the lungs, is the organ of gas exchange
The three fetal shunts
The ductus venosus skips the liver — the other two skip the lungs
Remnants: the ductus venosus becomes the ligamentum venosum, the foramen ovale the fossa ovalis, and the ductus arteriosus the ligamentum arteriosum. Prostaglandin E1 (alprostadil) keeps the ductus open for ductal-dependent heart defects; indomethacin or ibuprofen helps close a patent ductus in preterm infants.
How the shunts close at birth
Lung resistance falls, systemic resistance rises — the shunts close
Functional closure: foramen ovale about 1–2 hours after birth; ductus arteriosus within a few days (anatomic over weeks to months); ductus venosus within the first week in most term newborns, later in preterm newborns. Anatomic foramen ovale closure is complete in only about half of infants by 6 months; about 1 in 4 adults keeps a patent foramen ovale.
When transition fails
Hypoxia, acidosis and cold stress keep the shunts open
Abnormal transition: persistent cyanosis with SpO₂ below 90% on room air, or an ongoing oxygen need, after the first hour of life. In PPHN the foot (post-ductal) reading is typically 5% or more below the right hand (pre-ductal).
Acrocyanosis or central cyanosis?
Blue hands and feet are expected early — blue lips never are
| Acrocyanosis | Central cyanosis | |
|---|---|---|
| Where | Hands and feet | Lips, tongue or trunk |
| Normal? | Expected in the first 24–48 hours | Never normal |
| Nurse does | Recognize it as an expected finding | Check SpO₂ and report |
CCHD pulse-oximetry screen
Right hand (pre-ductal) and a foot (post-ductal), at 24 hours or later
Current AAP algorithm (2020, endorsed 2025): 95% is now required in both hand and foot (formerly either), with one repeat instead of two. Screen as late as possible before an earlier discharge.
Red flags
A soft murmur in the first day or two can be transitional while the shunts close — report it rather than dismiss it.
Nursing priorities
Teach the family
Before birth the placenta does gas exchange and three shunts skip the liver and lungs; first breaths and cord clamping shift the pressures and close them. Blue lips, tongue or trunk are never normal — check SpO₂ and report.
Sources · Maternal-Newborn Nursing 22.2: Physiological Adaptation and Transition (OpenStax) · Anatomy and Physiology 2e 28.3: Fetal Development (OpenStax) · Anatomy and Physiology 2e 28.5: Adjustments of the Infant at Birth (OpenStax) · Anatomy and Physiology 2e 28.2: Embryonic Development (OpenStax) · Maternal-Newborn Nursing Ch. 22 Key Terms (OpenStax) · Newborn Screening for Critical Congenital Heart Disease: A New Algorithm (AAP Clinical Report, Pediatrics 2025) · Updated Strategies for Pulse Oximetry Screening for CCHD (Pediatrics 2020) · Newborn Screening for Critical Congenital Heart Defects (CDC) · Persistent Pulmonary Hypertension of the Newborn (MSD Manual Professional) · Patent Ductus Arteriosus (MSD Manual Professional) · CCHD Newborn Screening Algorithm Card (Texas DSHS) · Isolated Single Umbilical Artery (Arch Dis Child) · Prenatal Detection of Cardiac Anomalies with Single Umbilical Artery (J Pregnancy) · Overview of Congenital Cardiovascular Anomalies (MSD Manual Professional) · Follow your facility's protocol for CCHD screening.
Fetal Circulation & Transition at Birth
Fetal circulation is the blood flow pattern before birth, when the placenta rather than the lungs exchanges gases and three shunts route blood past the liver and the fluid-filled lungs. The umbilical cord has two arteries and one vein, and the vein carries oxygenated blood to the fetus. The ductus venosus bypasses the liver, while the foramen ovale and the ductus arteriosus bypass the lungs. At birth, the first breaths lower pulmonary resistance and cord clamping raises systemic resistance, so the foramen ovale flap shuts within hours and rising oxygen closes the ductus arteriosus over a few days. Hypoxia, acidosis and cold stress can keep the shunts open, a failed transition called persistent pulmonary hypertension of the newborn. Blue hands and feet are expected in the first day or two, but blue lips, tongue or trunk never are. Pulse-oximetry screening for critical heart disease at 24 hours or later passes only at 95 percent or higher in both the right hand and a foot, with a difference of 3 percent or less.
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