Antepartum Fetal Assessment and Testing
Core concepts
Antepartum testing estimates fetal well-being before labor. The nonstress test evaluates fetal heart rate accelerations over a set period; reactivity is generally reassuring. The contraction stress test assesses whether the fetus tolerates contractions; a negative test means no late decelerations. The biophysical profile combines ultrasound findings (breathing, movement, tone, amniotic fluid volume) with a nonstress test.
Each test has a purpose and a limitation. The nonstress test is simple but can be non-reactive because of fetal sleep, so stimulation or extended observation is used. Amniotic fluid volume reflects chronic placental function. Doppler studies assess umbilical artery flow in growth-restricted fetuses.
Traps
Questions often ask what a negative contraction stress test means (reassuring) versus a positive one (late decelerations, concerning). Another trap is interpreting a non-reactive nonstress test as automatically abnormal without considering fetal sleep or gestational age. Also distinguish screening tests from diagnostic tests.
Rule of thumb
A reactive nonstress test with normal amniotic fluid is generally reassuring; a non-reactive test should prompt further evaluation rather than immediate delivery.
Worked example
A growth-restricted fetus has a non-reactive nonstress test and decreased amniotic fluid. The combination suggests chronic uteroplacental insufficiency, and further assessment and delivery planning are indicated based on gestational age and severity.