Antenatal Fetal Surveillance

The primary objective of antenatal fetal surveillance is to mitigate the risk of stillbirth. For nearly 4 decades, techniques assessing fetal heart rate (FHR) patterns, alongside real-time ultrasonography and umbilical artery Doppler velocimetry, have been used to monitor fetal well-being. These methods are crucial for evaluating the risk of fetal death in pregnancies with preexisting maternal conditions, such as diabetes mellitus, or those complicated by issues such as fetal growth restriction. FHR patterns, activity levels, and muscle tone are indicators that can be affected by hypoxemia and acidemia. When a fetus experiences hypoxemia, blood flow redistribution can lead to reduced renal perfusion and oligohydramnios. Techniques such as cardiotocography, real-time ultrasonography, and monitoring maternal perception of fetal movements are used to detect potential uteroplacental compromise. Identifying fetal compromise allows for intervention before metabolic acidosis can progress to fetal death. However, sudden and severe changes in fetal status, such as placental abruption or umbilical cord accidents, are typically unpredictable and less preventable through these tests.

The American College of Obstetricians and Gynecologists (ACOG) has provided general recommendations on when to initiate antenatal fetal surveillance based on the risk of stillbirth; however, strict guidelines have not been established due to the limited amount of evidence-based studies. Consequently, the ACOG encourages antenatal fetal surveillance to be individualized, including initiation, modalities utilized, and frequency, especially in high-risk cases where surveillance might begin at an age where delivery benefits perinatal outcomes. Antenatal fetal surveillance is indicated for conditions with a stillbirth incidence higher than 0.8 per 1000 and a relative risk or odds ratio for stillbirth >2.0 compared to unaffected pregnancies. In the absence of gestational age-adjusted data, ACOG suggests initiating surveillance at 32, 36, or 39 weeks of gestation. Shared decision-making between the patient and clinician is essential, particularly for pregnancies at a high risk of stillbirth or for those with multiple complicating factors. This approach is crucial when dealing with fetal anomalies or initiating surveillance near the threshold of viability, where patient preferences significantly influence care decisions.

Various surveillance methods include maternal perception of fetal movement, contraction stress tests (CSTs), nonstress tests (NSTs), biophysical profiles (BPPs), modified BPPs, and umbilical artery Doppler velocimetry. Generally, normal results from these tests are reassuring due to their low false-negative rates. However, antenatal fetal surveillance using any modality may not accurately reflect a significantly affected fetus during acute distress and is less effective at predicting stillbirths resulting from acute maternal-fetal status changes. In addition, some maternal conditions may cause temporary abnormal results during fetal testing that improve as the maternal condition improves. Therefore, abnormal test results should be interpreted within the broader clinical context, with further testing or intervention guided by the overall maternal and fetal condition.

In cases of decreased maternal perception of fetal movement, further assessment with NSTs, CSTs, BPPs, or modified BPPs is recommended. Abnormal findings typically lead to additional testing or consideration of delivery. The management of equivocal or abnormal BPP scores varies based on gestational age. For scores of 4 or lower, delivery is often indicated unless the pregnancy is less than 32 weeks, where extended monitoring may be appropriate. Ultimately, abnormal test results necessitate careful evaluation to avoid unnecessary interventions. Continuous intrapartum monitoring is advisable if delivery is attempted. Although fetal kick counting is a simple method to assess fetal well-being, its effectiveness in preventing stillbirth is not well-established and might lead to increased medical interventions.