Antenatal fetal surveillance: CTG, biophysical profile, umbilical artery Doppler

A 34-year-old woman with type 1 diabetes is 34 weeks pregnant and you are deciding how to watch her fetus for the rest of the pregnancy. The choice of modality — a cardiotocograph, a biophysical profile, or an umbilical artery Doppler — is not a matter of which is "best" in the abstract, but of which question you are asking: is the fetus hypoxic now, or is the placenta failing over time? This topic is the high-yield junction where surveillance strategy, Doppler physiology and the modified BPP meet, and it is where the candidate who knows which test for which fetus separates from the one who reaches for a CTG every time. ^[1]

Overview and definition

Antepartum fetal surveillance is the set of tests used to assess fetal well-being in pregnancies at increased risk of fetal death, with the goal of identifying a compromised fetus early enough to intervene. ^[1]

The governing idea: the modalities answer different questions. ^[1][2]

• Acute markers (CTG, BPP) reflect the fetus's current acid-base and behavioural status. A normal CTG reassures you for hours to a few days, not for weeks. ^[1]
• Chronic marker (umbilical artery Doppler) reflects placental function and long-term substrate delivery — it predicts the trajectory of compromise over weeks.

Matching the modality to the question is the skill. A CTG is excellent for the post-term or diabetic fetus at risk of acute hypoxia; it is the wrong primary test for the growth-restricted fetus with failing placentation, where Doppler is indicated.^[1][2]