What are the guidelines for managing fetal growth restriction?

Guidelines on Fetal Growth Restriction

Definition and Diagnosis

Fetal growth restriction (FGR) should be defined as an ultrasonographic estimated fetal weight (EFW) or abdominal circumference below the 10th percentile for gestational age, using population-based references such as Hadlock. 1, 2

• Accurate pregnancy dating using first-trimester crown-rump length is essential before making this diagnosis, as incorrect dating is a common pitfall. 2, 3
• EFW is calculated using regression equations combining biparietal diameter, head circumference, abdominal circumference, and femur length. 2, 3
• Severe FGR is defined as EFW below the 3rd percentile, which carries increased risk regardless of Doppler findings. 2, 3

Classification by Timing

• Early-onset FGR (diagnosed <32 weeks): More severe with substantial placental abnormalities, elevated hypoxia risk, and worse perinatal outcomes. 2
• Late-onset FGR (diagnosed ≥32 weeks): Associated with milder placental deficiencies and lower perinatal morbidity. 2

Prevention Strategies

Low-dose aspirin (100-150 mg daily) must be initiated before 16 weeks of gestation in women with major risk factors for placental insufficiency, including prior preeclampsia <34 weeks or prior FGR <5th percentile. 1, 2

• Aspirin is more effective when started at ≤16 weeks and at doses of 100 mg compared to 60 mg. 2
• Do not use low-molecular-weight heparin solely for prevention of recurrent FGR. 1, 2
• Do not use sildenafil or activity restriction for in utero treatment of FGR. 1, 2
• Smoking cessation at any stage of pregnancy is universally recommended and remains one of the most modifiable risk factors. 1, 2

Diagnostic Workup When FGR is Detected

A detailed obstetrical ultrasound examination (CPT code 76811) must be performed with early-onset FGR (<32 weeks). 1, 2

Genetic Testing Recommendations:

• Offer chromosomal microarray analysis when FGR is detected with fetal malformation, polyhydramnios, or both, regardless of gestational age. 1, 3
• Offer chromosomal microarray analysis when unexplained isolated FGR is diagnosed at <32 weeks of gestation. 1, 3
• Do not screen for toxoplasmosis, rubella, or herpes in the absence of other risk factors. 1
• Perform polymerase chain reaction for cytomegalovirus in women with unexplained FGR who elect diagnostic testing with amniocentesis. 1

Surveillance Protocol

Once FGR is diagnosed, serial umbilical artery (UA) Doppler assessment must be performed to assess for deterioration. 1, 2, 3

Doppler Surveillance Frequency:

• Normal UA Doppler: Every 2 weeks 1, 2
• Decreased end-diastolic velocity (flow ratios >95th percentile) or severe FGR (EFW <3rd percentile): Weekly 1, 2
• Absent end-diastolic velocity: 2-3 times per week 1, 2, 3
• Reversed end-diastolic velocity: Requires hospitalization, immediate antenatal corticosteroids, and heightened surveillance with cardiotocography at least 1-2 times per day 1, 2

Additional Surveillance:

• Cerebral Doppler studies (middle cerebral artery and cerebroplacental ratio) should be used in late-onset FGR (>32 weeks) to influence surveillance and delivery timing. 1
• Cardiotocography (nonstress testing) is recommended as the primary fetal surveillance method, with frequency increasing based on Doppler abnormalities. 1

Timing of Delivery

Delivery timing is determined by gestational age, EFW percentile, and Doppler findings, following this algorithm:

For Late-Onset FGR (≥32 weeks):

• EFW 3rd-10th percentile with normal UA Doppler: Deliver at 38-39 weeks 2, 3
• Decreased diastolic flow OR severe FGR (EFW <3rd percentile): Deliver at 37 weeks 2, 3
• Absent end-diastolic velocity: Deliver at 33-34 weeks 1, 2, 3
• Reversed end-diastolic velocity: Deliver at 30-32 weeks 1, 2, 3

For Early-Onset FGR (<32 weeks):

• Management requires intensive surveillance with consideration of delivery based on the entire clinical picture, including ductus venosus Doppler and biophysical profile findings. 1
• The recommended gestation at delivery for absent end-diastolic velocity varies from 32-34 weeks, and for reversed end-diastolic velocity from 30-34 weeks, depending on the guideline. 1

Antenatal Interventions

Administer antenatal corticosteroids before delivery at <34 weeks of gestation (some guidelines extend to 35+6 weeks). 1, 2

Administer magnesium sulfate for neuroprotection in early-onset FGR (<32 weeks). 1, 2

Critical Pitfalls to Avoid

• Do not diagnose FGR without accurate first-trimester dating, as this leads to false-positive diagnoses. 2, 3
• Do not rely solely on cardiotocography for surveillance in FGR—umbilical artery Doppler is the primary test. 1, 4
• Do not perform routine third-trimester ultrasound screening in low-risk women, as this is not recommended. 1
• Recognize that not all small fetuses have true FGR—some are constitutionally small for gestational age (SGA) without placental insufficiency and have normal outcomes. 5
• No antenatal test can predict acute events such as placental abruption or cord accidents, so ongoing surveillance is essential even with reassuring tests. 6