A 28-year-old woman, gravida 1 para 0, at 41 weeks gestation comes to the hospital for antepartum fetal surveillance. She has noticed decreased fetal movement for the past few hours but has had no abdominal pain, leakage of fluid, or vaginal bleeding. Blood pressure is 126/82 mm Hg. The patient's pre-pregnancy BMI was 40 kg/m2, and she has gained 20 kg (44 lb) during the pregnancy. The pregnancy has otherwise been uncomplicated. Nonstress testing shows a baseline fetal heart rate of 140/min, moderate variability, and no accelerations for >40 minutes. Two contractions are observed on the tocodynamometer. The fetal heart rate decreased to 130/min after the peak of each contraction and lasted for a minute, gradually returning to baseline after resolution of the contraction. Ultrasound shows a fetus in cephalic presentation, a loop of umbilical cord near the fetal neck, an estimated fetal weight at the 35th percentile for gestational age, and a single deepest pocket of amniotic fluid of 1 cm (normal: ≥2 and <8). The biophysical profile results are shown below.
| Biophysical profile component | Score |
| Nonstress test | 0 |
| Amniotic fluid volume | 0 |
| Fetal movements | 2 |
| Fetal tone | 2 |
| Fetal breathing movements | 0 |
Which of the following is the most likely cause of this patient's biophysical profile results?
Biophysical profile* | |
Component | Normal finding |
Nonstress test (NST) | Reactive fetal heart rate monitoring |
Amniotic fluid volume | A single deepest vertical pocket > 2 cm × 1 cm is present or amniotic fluid index > 5 cm |
Fetal movements | ≥3 discrete body or limb movements |
Fetal tone | ≥1 episodes of active extension & flexion of an extremity |
Fetal breathing movements | ≥1 breathing episodes for ≥30 sec |
*Continuous ultrasound observation up to 30 min. | |
Pregnancies at ≥41 weeks gestation are at increased risk of stillbirth. In these pregnancies, placental aging leads to decreased placental function, which limits fetal perfusion during contractions and induces intermittent fetal hypoxemia. On nonstress testing, fetal hypoxemia presents as late decelerations, decelerations that gradually nadir after the contraction's peak (as seen in this patient).
Progressive placental dysfunction can lead to chronic fetal hypoxemia (ie, uteroplacental insufficiency), which causes CNS suppression and potential fetal demise. To maintain CNS function, the hypoxemic fetus preferentially distributes blood to the brain. Decreased perfusion to the kidney results in decreased urine production and oligohydramnios (single deepest pocket <2 cm). Decreased blood supply to peripheral muscle results in decreased fetal activity (eg, movement, tone) that may be felt by the mother.
Patients with signs of suspected fetal hypoxemia (eg, decreased fetal movement, late decelerations) require a biophysical profile (BPP) to evaluate fetal oxygenation. The BPP includes a nonstress test and ultrasound assessment of amniotic fluid volume and fetal activity. Each BPP component is scored 0 or 2 for a total score of 0-10. Normal scores (8 or 10) exclude fetal hypoxemia. In contrast, abnormal BPP scores (particularly ≤4) suggest severe hypoxemia with imminent risk of stillbirth; delivery is typically indicated.
(Choice A) Fetal head compression causes a normal parasympathetic response that presents as early decelerations, gradual heart rate decelerations that nadir at the peak of the contraction. Early decelerations do not indicate chronic hypoxemia and therefore do not cause an abnormal BPP score.
(Choice B) Fetal sleep cycles can cause decreased fetal movement and nonreactive nonstress testing. However, they do not cause late decelerations or oligohydramnios.
(Choice C) Intraamniotic infection can present with oligohydramnios if associated with premature rupture of membranes (not seen in this patient). Fetal monitoring usually reveals tachycardia (>160/min).
(Choice D) Nuchal cords (eg, loops of umbilical cord around the fetal neck) are associated with variable decelerations, which are abrupt (≥15/min) decreases in fetal heart rate below the baseline of varying depth and duration that represent acute cord compression and interruption of fetal perfusion. Nuchal cords do not cause oligohydramnios or decreased fetal breathing movements.
(Choice E) Polyhydramnios (amniotic fluid index ≥24 cm or single deepest pocket ≥8 cm) does not affect BPP score.
Educational objective:
A biophysical profile (BPP) is performed in patients at risk for uteroplacental insufficiency (eg, ≥41 weeks gestation). Chronic hypoxemia causes an abnormal BPP score and suggests imminent risk of fetal demise; delivery is typically indicated.