What is the management plan for a pregnant woman with fetal growth restriction, measuring small for gestational age?

Management of Fetal Growth Restriction (Small for Gestational Age)

For a pregnant woman measuring small for gestational age, immediately confirm accurate pregnancy dating, perform umbilical artery Doppler assessment, and initiate serial surveillance with delivery timing based on gestational age, estimated fetal weight percentile, and Doppler findings. 1

Initial Diagnostic Workup

Confirm Diagnosis and Dating

• Verify pregnancy dating using first-trimester crown-rump length (11-14 weeks) before diagnosing FGR, as accurate dating is essential 1, 2
• Define FGR as estimated fetal weight (EFW) or abdominal circumference below the 10th percentile for gestational age using population-based references such as Hadlock 1
• Severe FGR is defined as EFW below the 3rd percentile, which carries increased risk regardless of Doppler findings 1

Detailed Ultrasound Examination

• Perform detailed fetal anatomic examination to identify structural abnormalities, particularly when FGR is diagnosed before 32 weeks 3, 1
• Measure head circumference, abdominal circumference, and femur length to calculate EFW using Hadlock's formula 2
• Assess amniotic fluid volume, as this is critical in all cases 3

Genetic Testing Considerations

• Offer chromosomal microarray analysis when FGR is detected with malformations or when unexplained isolated FGR is diagnosed before 32 weeks 3, 1
• Approximately 10% of fetuses with growth restriction have congenital anomalies 3

Surveillance Protocol Based on Severity

Umbilical Artery Doppler Assessment

Umbilical artery Doppler is the first-line surveillance tool and must be performed in all suspected FGR cases 4, 1, 2

Surveillance frequency based on Doppler findings:

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

Additional Doppler Studies for Late-Onset FGR

• In late-onset FGR (>32 weeks), use cerebral Doppler studies (middle cerebral artery and cerebroplacental ratio) to influence surveillance and delivery timing 4, 1
• The combination of biometric parameters with Doppler criteria of placental insufficiency (uterine artery or cerebroplacental ratio) provides better risk stratification than umbilical artery Doppler alone 5

Growth Monitoring

• Repeat growth scans at intervals of no less than 2 weeks, ideally 3 weeks apart 2
• Guidelines show inconsistency in recommended frequency (2-4 weeks), but consensus favors 2-3 week intervals 4

Delivery Timing Algorithm

Late-Onset FGR (≥32 weeks)

Delivery timing based on EFW percentile and Doppler findings 1:

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

Early-Onset FGR (<32 weeks)

• Early-onset FGR is typically more severe with substantial placental abnormalities and elevated hypoxia 1
• Delivery timing follows the same Doppler-based algorithm but requires more intensive surveillance 1
• Referral to Level IIb or III maternity ward is recommended for EFW <1500g or potential birth before 32-34 weeks 2

Antenatal Interventions

Corticosteroids

• Administer antenatal corticosteroids before delivery at <34 weeks (some guidelines extend to 35+6 weeks) 1, 2
• This is universally agreed upon across all guidelines 1

Magnesium Sulfate for Neuroprotection

• Use magnesium sulfate for neuroprotection in early-onset FGR (<32 weeks) when preterm delivery is anticipated 1, 6
• Prescribe for preterm deliveries before 32-33 weeks 2

Mode of Delivery

• Systematic cesarean delivery for FGR is not recommended 2
• If vaginal delivery is attempted, continuous fetal heart rate monitoring during labor is mandatory with lower threshold for intervention 2
• Regional anesthesia is preferred for both vaginal delivery trials and planned cesareans 2

Prevention Strategies for Future Pregnancies

Low-Dose Aspirin

• Initiate low-dose aspirin (100-150 mg daily) before 16 weeks of gestation in women with major risk factors for placental insufficiency, including prior preeclampsia <34 weeks or prior FGR <5th centile 1, 2
• Aspirin is more effective when started at ≤16 weeks and at doses of 100 mg compared to 60 mg 1
• Take aspirin in the evening or at least 8 hours after awakening 2

Smoking Cessation

• Smoking cessation at any stage of pregnancy is universally recommended and should be emphasized 1

Interventions NOT Recommended

• Low-molecular-weight heparin should not be used solely for prevention of recurrent FGR 1
• Sildenafil or activity restriction should not be used for in utero treatment of FGR 1

Critical Pitfalls to Avoid

• Failure to detect SGA prenatally: Only 25% of SGA births are detected prenatally, and among preterm SGA, composite neonatal morbidity is significantly higher when undetected 7
• Relying solely on fundal height in obese patients: Ultrasound scans should be considered in women with obesity and/or fibroids as fundal height measurements are unreliable 4
• Delaying delivery in severe FGR: Evidence suggests delivery at 38 weeks in suspected FGR may be optimum unless there are earlier concerns about fetal well-being, as stillbirth risk increases markedly from 38 weeks in SGA babies 4
• Induction before 38 weeks without clear indication: Induction of late FGR at term before 38 weeks may increase neonatal admission without improving perinatal outcomes 5