Which structure connects the pulmonary artery to the aorta in the fetus?

A. Clamping of the umbilical cord eliminates the low-resistance placental circulation, which previously accounted for a significant portion of fetal blood flow. This increases systemic vascular resistance as blood is now redirected through the neonatal systemic circulation.

B. The first breath and lung expansion lead to a dramatic decrease in pulmonary vascular resistance, which increases left atrial pressure. This shift in pressure gradients contributes to the closure of fetal shunts and an increase in systemic vascular resistance.

D. Closure of the foramen ovale occurs due to increased left atrial pressure following lung expansion and decreased right atrial pressure after umbilical cord clamping. This closure redirects blood flow through the systemic circulation, contributing to the rise in systemic vascular resistance.

Rationale for incorrect answers

C. Prostaglandin E2 levels decrease at birth, not increase. This decline facilitates the closure of the ductus arteriosus and other fetal shunts. Increased prostaglandin E2 would maintain patency of these shunts, opposing the rise in systemic vascular resistance.

E. Activation of the renal system is not an immediate factor in the increase in systemic vascular resistance at birth. While renal function begins to regulate fluid and electrolyte balance postnatally, it does not directly influence the acute changes in vascular resistance during the transition to neonatal circulation.

Take home points

• Clamping the umbilical cord eliminates the low-resistance placental circuit, increasing SVR.
• Lung expansion reduces pulmonary vascular resistance and redirects blood flow.
• Closure of fetal shunts, including the foramen ovale, contributes to increased SVR.
• Prostaglandin E2 levels decrease at birth, facilitating shunt closure.

Biophysical profile (BPP) is a prenatal test used to assess fetal well-being by evaluating fetal heart rate, breathing movements, tone, and amniotic fluid volume. It combines ultrasound and non-stress test findings. Normal BPP scores range from 8–10, indicating low risk of fetal compromise, while scores below 6 suggest potential hypoxia or acidosis.

Rationale for correct answers

A. Fetal heart rate accelerations are assessed using a non-stress test, which evaluates the fetal response to movement. Two or more accelerations of at least 15 beats per minute lasting 15 seconds within 20 minutes are considered normal.

B. Fetal breathing movements are observed via ultrasound. Normal breathing movements include rhythmic diaphragmatic contractions lasting at least 30 seconds within a 30-minute observation period.

D. Fetal tone is assessed by observing movements such as limb flexion and extension. Normal tone includes at least one episode of active extension with return to flexion within 30 minutes.

Rationale for incorrect answers

C. Maternal blood pressure is not a component of the biophysical profile. While maternal health is critical for fetal well-being, blood pressure is assessed separately and does not directly contribute to the BPP score.

E. Cervical length is not evaluated in a biophysical profile. It is assessed during pregnancy to predict preterm labor risk but is unrelated to fetal well-being parameters measured in the BPP.

Take home points

• Biophysical profile evaluates fetal heart rate, breathing movements, tone, and amniotic fluid volume.
• Normal BPP scores range from 8–10; scores below 6 indicate potential fetal compromise.
• Maternal blood pressure and cervical length are not components of the BPP.
• BPP combines ultrasound findings with non-stress test results.