SUMMARY:

ACOG / SMFM released a guidance update on fetal growth restriction (FGR). While there is currently no clear consensus on the definition, evaluation, and management, FGR is associated with adverse perinatal outcomes. Therefore, timely diagnosis and management is key to optimizing long term benefit. Ultrasound and fundal height measurement are important physical exam diagnostic maneuvers. Early delivery and expectant management have similar outcomes thus creating deliberate birth plans should be discussed.

Key Terms and Definitions

• FGR: EFW or AC <10th percentile for gestational age
  • Symmetric: Global growth restriction | Early insult
  • Asymmetric: Head-sparing with generally better outcomes
• Small for gestational age (SGA): Newborn birthweight <10th percentile for gestational age

Risk Factors

Maternal Disease

• Hypertensive disorders
  • Chronic hypertension
  • Gestational hypertension and preeclampsia
• Kidney disease
• Endocrine
  • Pregestational diabetes mellitus
• Autoimmune
  • SLE
  • Antiphospholipid syndrome
• Congenital heart disease (see ‘Learn More – Primary Sources’ for additional information)
  • Highest risk: Cyanotic heart disease | Reduced cardiac output

Note: Nutrition, oxygenation, and cardiovascular adaptation to pregnancy (placental perfusion) are underlying maternal factor mechanisms that impact fetal growth

Fetal Factors

• Multiple gestation
• Teratogenic exposures
  • Medications (e.g. fetal hydantoin syndrome)
  • Substance abuse (modifiable risk) including alcohol, cocaine and smoking
  • Intrauterine infections (e.g., CMV, rubella, syphilis)
• Genetics:
  • Aneuploidy: Trisomy 13 and trisomy 18 commonly associated with FGR
  • Single gene disorders
  • Multifactorial: Congenital malformations (heart disease, gastroschisis)

Placental Anomalies

• Abruption | Infarction | Circumvallate shape | Hemangioma | Chorioangioma
• Umbilical cord anomalies
  • Velamentous or marginal insertion
  • Single umbilical artery

Note: Placental implantation abnormalities (e.g. placental accreta spectrum, previa) not associated with FGR

Evaluation and Screening Methods

• Fundal height measurements
  • Begin at 24 weeks gestation
  • Perform at each prenatal visit
  • 3 cm discrepancy “proposed for identifying a fetus that may be growth restricted”
  • Limitations
    • Maternal obesity | Fibroids | Multiple gestation
• Ultrasound
  • Preferred method of evaluation
  • Measurements include
    • BPD
    • HC
    • AC
    • FL
• UA Doppler velocimetry
  • Reduces perinatal death when added to antepartum testing
  • Absent or reversed end-diastolic flow increases risk for perinatal mortality
  • Evaluation of the fetal ductus venosus has not been shown to improve perinatal outcomes (TRUFFLE study)

Note: No current evidenced based screening methods or preventative measures such as bed rest have demonstrated improved perinatal outcomes

KEY POINTS:

Management

• Address modifiable risk factors, for example
  • Screen for fetal alcohol exposure
  • Discuss and encourage reduction in smoking and/or smoking cessation
    • Smoking is associated with 3.5 increased risk of SGA newborns
• Genetic counseling
  • FGR alone may be associated with genetic syndromes and aneuploidy
  • Combined FGR and fetal structural abnormalizes increase aneuploidy risk and warrants genetic counseling referral
• Depending on clinical scenario
  • Serial ultrasounds q3-4 weeks for growth and AFV
  • Do not measure fetal growth more often than every 2 weeks (measurements will be within error of the test)
  • Fetal assessment (NSTs or BPPs): “…should not begin before a gestational age when delivery would be considered for perinatal benefit”
• Mode of delivery
  • Reserve cesarean section for obstetric/neonatal indications
  • Cesarean section and is not indicated for FGR in isolation

Timing of Delivery

• Normal UA Doppler and EFW 3 to 10th percentile: 38w0d to 39w0d
• EFW <3rd percentile (severe FGR): 37w0d
• Decreased UA flow without absent end diastolic flow: 37w0d to 37w6d
• Absent end diastolic flow: 33w0d to 34w0d
• Reversed end diastolic flow: 30w0d to 32w0d
• With oligohydramnios or concurrent conditions (e.g., preeclampsia, chronic hypertension): 34w0d to 37w6d

Note: If delivery planned <34 weeks, deliver at center with a NICU and consult MFM

When to Give Antepartum Corticosteroids

• < 33w6d (anticipated delivery)
• 34w0d-36w6d (late preterm) if risk
  • No previous corticosteroids
  • Anticipate delivery within 7 days

Note: “Consider” magnesium sulfate (neuroprotection) if delivery <32w0d

Future Pregnancies

• Counsel regarding 20% recurrence risk
• Review history to identify modifiable factors and/or treat maternal disease
• In subsequent pregnancies

…it may be reasonable to perform serial ultrasonography for growth assessment, although the optimal surveillance regimen has not been determined.

Maternal history of a prior SGA newborn with normal fetal growth in the current pregnancy is not an indication for antenatal fetal heart rate testing, biophysical profile testing, or umbilical artery Doppler velocimetry

Note: There is insufficient evidence to routinely administer aspirin to prevent SGA in this population

Learn More – Primary Sources

ACOG Practice Bulletin 227: Fetal Growth Restriction

Effect of Maternal Heart Disease on Fetal Growth

Locate a Maternal Fetal Medicine Specialist

Maternal Fetal Medicine Specialist Locator-SMFM

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