What are the new guidelines for 2024 regarding the management of Fetal Growth Restriction (FGR)?

Fetal Growth Restriction Guidelines 2024

Definition and Diagnostic Criteria

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

Classification by Gestational Age

• Early-onset FGR: Diagnosed before 32 weeks of gestation, typically more severe with substantial placental implantation abnormalities and elevated hypoxia 2, 3
• Late-onset FGR: Diagnosed at or after 32 weeks, associated with milder placental deficiencies and lower perinatal morbidity 2, 3

Severity Stratification

• Severe FGR: EFW below the 3rd percentile carries increased risk of adverse perinatal outcomes regardless of Doppler findings 2
• High-risk FGR: EFW <3rd centile OR abnormal umbilical artery (UA), uterine artery, middle cerebral artery (MCA), or cerebroplacental ratio (CPR) Doppler 1

For early-onset FGR (<32 weeks), three solitary diagnostic parameters exist: AC <3rd centile, EFW <3rd centile, or absent end-diastolic velocity in the UA 1

For late-onset FGR (≥32 weeks), two solitary parameters apply: AC or EFW <3rd centile, plus four contributory parameters including EFW or AC <10th centile, crossing centiles by >2 quartiles, CPR <5th centile, or UA pulsatility index >95th centile 1

Screening and Prevention

Risk Assessment

• Perform universal risk stratification at booking to identify high-risk pregnancies requiring enhanced surveillance 4, 5, 6
• Low-risk pregnancies: Serial fundal height measurement from 24-26 weeks on customized charts; trigger ultrasound if <10th centile or static/slow growth 1
• High-risk pregnancies: Serial ultrasound surveillance in third trimester rather than fundal height alone 1

Prevention Strategies

Low-dose aspirin (100-150 mg daily) should 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 centile. 1

• Aspirin is more effective when started at ≤16 weeks and at doses of 100 mg compared to 60 mg 1
• Do NOT use low-molecular-weight heparin solely for prevention of recurrent FGR 1
• Do NOT use sildenafil or activity restriction for in utero treatment of FGR 1
• Smoking cessation at any stage of pregnancy is universally recommended 1

Diagnostic Workup

Ultrasound Evaluation

• Perform detailed obstetrical ultrasound examination (CPT 76811) with early-onset FGR (<32 weeks) 1, 2
• Accurate pregnancy dating using first-trimester crown-rump length is essential before diagnosing FGR 2
• EFW is generated using regression equations combining biparietal diameter, head circumference, AC, and femur length 2

Genetic Testing

Offer fetal diagnostic testing with chromosomal microarray analysis when:

• FGR is detected with fetal malformation, polyhydramnios, or both (regardless of gestational age) 1, 2
• Unexplained isolated FGR is diagnosed at <32 weeks of gestation 1, 2

Infectious Workup

• Do NOT routinely screen for toxoplasmosis, rubella, or herpes in FGR pregnancies without other risk factors 1
• Consider polymerase chain reaction for cytomegalovirus in women with unexplained FGR who elect diagnostic amniocentesis 1

Surveillance Protocol

Umbilical Artery Doppler

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

• Normal UA Doppler: Every 2 weeks 1
• 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, 7
• Reversed end-diastolic velocity: Hospitalization, administer antenatal corticosteroids, heightened surveillance 1

Cerebral Doppler Studies

• In late-onset FGR (≥32 weeks) with normal UA Doppler, add MCA Doppler and CPR to influence surveillance and delivery timing 1, 7
• Cerebral Doppler should be performed every 2-3 weeks if normal 1

Growth Interval Scans

• Serial growth scans every 2-4 weeks after FGR diagnosis, with specific interval depending on severity 7, 6
• More frequent assessment (weekly or 2-3 times weekly) when severe Doppler abnormalities develop 7

Timing of Delivery

Late-Onset FGR (≥32 weeks)

Delivery timing based on EFW percentile and Doppler findings:

• EFW 3rd-10th percentile with normal UA Doppler: 38-39 weeks 2, 7
• Decreased diastolic flow OR severe FGR: 37 weeks 2
• Absent end-diastolic velocity: 33-34 weeks 2
• Reversed end-diastolic velocity: 30-32 weeks 2

Early-Onset FGR (<32 weeks)

• Delivery timing varies from 32-34 weeks for absent end-diastolic velocity and 30-34 weeks for reversed end-diastolic velocity depending on specific guideline 1
• Use cardiotocography surveillance to plan delivery timing 1

Antenatal Interventions

Corticosteroids

• Universal agreement: Administer antenatal corticosteroids before delivery at <34 weeks 1
• Some guidelines extend to 35+6 weeks 1

Magnesium Sulfate

• General consensus supports magnesium sulfate for neuroprotection in early-onset FGR (<32 weeks) 1, 7

Common Pitfalls

• Avoid using customized vs. population-based standards inconsistently - stick with population-based references like Hadlock as recommended 1, 2
• Do not delay genetic testing in early-onset FGR - offer chromosomal microarray at diagnosis <32 weeks 1, 2
• Do not rely on fundal height alone in high-risk pregnancies - these require serial ultrasound surveillance 1
• Avoid routine third-trimester ultrasound screening in low-risk populations - not recommended for FGR detection 1