What are the key recommendations in the International Society of Ultrasound in Obstetrics and Gynecology (ISUOG) guideline for managing small for gestational age (SGA) pregnancies?

Key Recommendations in the ISUOG Small for Gestational Age (SGA) Guideline

The ISUOG guideline defines SGA as an estimated fetal weight (EFW) or abdominal circumference (AC) below the 10th percentile for gestational age, with fetal growth restriction (FGR) representing pathological smallness due to placental dysfunction. 1, 2

Diagnosis and Definition

• SGA is defined as EFW or AC <10th percentile 1
• Severe FGR is defined as EFW <3rd percentile 2
• Population-based fetal growth references (such as Hadlock) are recommended for determining fetal weight percentiles 1
• Customized growth charts are recommended by some guidelines but not universally 1

Screening and Prevention

• Early pregnancy risk assessment is essential 1
• Low-dose aspirin is recommended before 16 weeks gestation for women with major risk factors for placental insufficiency 1
• Smoking cessation is universally recommended to prevent SGA 1
• Routine third-trimester ultrasound screening is not recommended for low-risk women 1
• Serial fundal height measurement is recommended in the third trimester 1

Ultrasound Assessment

• Detailed obstetrical ultrasound examination should be performed with early-onset FGR (<32 weeks) 1
• Fetal biometric parameters should include:
  • Biparietal diameter (BPD)
  • Head circumference (HC)
  • Abdominal circumference (AC)
  • Femur length (FL) 2, 3

Doppler Assessment

• Once FGR is diagnosed, serial umbilical artery (UA) Doppler assessment should be performed to monitor for deterioration 1
• Recommended frequency of UA Doppler assessment:
  • Every 2 weeks if normal
  • Weekly with increased resistance (pulsatility index >95th percentile) or severe FGR (EFW <3rd percentile)
  • 2-3 times per week with absent end-diastolic velocity (AEDV)
  • More frequently with reversed end-diastolic velocity (REDV) 1, 2
• Cerebral Doppler studies (middle cerebral artery) are recommended in late-onset FGR (>32 weeks) 1

Management Based on Doppler Findings

• With AEDV: Hospitalization, daily cardiotocography (CTG), twice weekly UA Doppler, and amniotic fluid assessment 1
• With REDV: Hospitalization, administration of antenatal corticosteroids, heightened surveillance with CTG at least 1-2 times daily, and consideration of delivery 1
• Weekly CTG testing is suggested after viability for FGR without AEDV/REDV 1

Timing of Delivery

• For AEDV: Consider delivery no later than 34 weeks gestation 1
• For REDV: Consider delivery no later than 30-32 weeks gestation 1
• For late-onset FGR with abnormal Doppler studies: Delivery at 37-38 weeks 1
• For FGR with normal Doppler studies: Delivery between 37-40 weeks 1

Antenatal Interventions

• Antenatal corticosteroids for fetal lung maturation between 24+0 and 34+0 weeks gestation 1
• Magnesium sulfate for neuroprotection before delivery at <32 weeks 1
• Activity restriction and sildenafil are not recommended for treatment of FGR 1
• Low-molecular-weight heparin is not recommended for prevention of recurrent FGR 1

Diagnostic Testing

• Prenatal diagnostic testing with chromosomal microarray analysis is recommended when FGR is diagnosed with fetal malformation or polyhydramnios 1
• Diagnostic testing with chromosomal microarray analysis should be offered for unexplained isolated FGR diagnosed at <32 weeks 1
• PCR for cytomegalovirus is recommended in women with unexplained FGR who elect amniocentesis 1

The ISUOG guideline provides a comprehensive, evidence-based approach to managing SGA pregnancies with clear protocols for surveillance and intervention based on the severity of growth restriction and Doppler findings.