What does a "late deceleration" indicate regarding fetal oxygen supply?

A late deceleration in fetal heart rate is a specific pattern observed during labor that indicates a potential compromise in fetal oxygen supply. This pattern typically occurs after a contraction has started and continues to decrease in heart rate, with the lowest point occurring after the peak of the contraction, indicating that the response of the fetal heart rate is delayed.

The occurrence of late decelerations points to a condition called uteroplacental insufficiency. This implies that there is decreased blood flow and, consequently, decreased oxygen delivery to the fetus, especially during and after uterine contractions. As the uterus contracts, the blood flow through the placenta can be temporarily reduced, which may lead to a lesser availability of oxygen for the fetus at that moment. After the contraction ends, it can take time for the blood flow and oxygen supply to stabilize, which is reflected in the delayed return of the heart rate to baseline.

Hence, late decelerations signal a critical need for closer monitoring and potentially intervention to ensure adequate oxygenation of the fetus, as they imply that the fetus may not be receiving enough oxygen during the periods of uterine contraction.