What test can be done to detect fetal growth restriction early on?

From the Guidelines

Ultrasound is the primary test to detect fetal growth restriction early in pregnancy, with serial measurements tracking fetal size and Doppler ultrasound assessing blood flow through the umbilical cord and fetal blood vessels 1.

Key Points to Consider

• Serial ultrasound measurements should be performed every 2-4 weeks in high-risk pregnancies to track fetal growth and detect potential growth restriction.
• Doppler ultrasound is a valuable tool in assessing fetal well-being and detecting placental insufficiency.
• Additional monitoring may include measuring amniotic fluid levels, as decreased fluid often accompanies growth restriction.
• Risk factors that warrant early and frequent monitoring include maternal hypertension, previous growth-restricted pregnancy, smoking, and certain medical conditions that affect placental function.

Recommendations for Detection and Management

• The Society for Maternal-Fetal Medicine recommends defining fetal growth restriction as an ultrasonographic estimated fetal weight or abdominal circumference below the 10th percentile for gestational age 1.
• Population-based fetal growth references, such as Hadlock, should be used to determine fetal weight percentiles 1.
• Serial umbilical artery Doppler assessment should be performed to assess for deterioration after fetal growth restriction is diagnosed 1.
• Delivery should be considered at 37 weeks of gestation in pregnancies with fetal growth restriction and an umbilical artery Doppler waveform with decreased diastolic flow but without absent or reversed end-diastolic velocity 1.

Important Considerations for Clinical Practice

• Early detection of fetal growth restriction is crucial to allow for increased surveillance, potential interventions, and optimal timing of delivery to prevent complications.
• The use of antenatal corticosteroids and magnesium sulfate for fetal neuroprotection should be considered in pregnancies with fetal growth restriction, especially in cases of preterm delivery 1.

From the Research

Tests for Detecting Fetal Growth Restriction

To detect fetal growth restriction early on, several tests can be utilized:

• Ultrasound assessment of fetal biometry at 32 or 36 weeks of gestation, which measures estimated fetal weight and abdominal circumference 2, 3
• Umbilical arterial Doppler sonography, which is considered the primary test for fetal growth restriction 4
• Nonstress test (NST), amniotic fluid assessment, biophysical profile (BPP), and selective venous Doppler sonography, which are used as supplementary tests 4
• Measurement of the ratio of soluble fms-like tyrosine kinase receptor 1 (sFLT1) to placental growth factor (PlGF) in combination with ultrasonic fetal biometry 5

Comparison of Ultrasound Assessments at 32 and 36 Weeks

Studies have compared the effectiveness of ultrasound assessments at 32 and 36 weeks of gestation in detecting fetal growth restriction:

• A systematic review and meta-analysis found that an ultrasound assessment at 36 weeks of gestation had better predictive accuracy for small-for-gestational-age neonates than an assessment at 32 weeks 2
• A randomized trial found that routine ultrasound examination at 36 weeks' gestation was more effective than that at 32 weeks' gestation in detecting fetal growth restriction and related adverse perinatal and neonatal outcomes 3

Risk Factors for Undetected Fetal Growth Restriction

Certain factors can increase the risk of severely growth-restricted fetuses remaining undelivered by 40 weeks gestation:

• Failure to receive an indicated third trimester ultrasound 6
• The presence of falsely reassuring third trimester ultrasound scan 6
• Booking under a low-risk rather than traditional collaborative models of care 6