Antenatal Fetal Surveillance: Indications and Timing

SUMMARY:

Antenatal fetal surveillance (AFS) aims at reducing intrauterine fetal demise however not all antenatal fetal surveillance has shown to improve perinatal outcomes. ACOG’s Committee Opinion addresses indications for AFS and aims to suggest surveillance specifically for conditions where stillbirth occurs more frequently than the false-negative rate of BPP (0.8 per 1,000) and conditions where stillbirth is >2 times more likely than pregnancies without the condition. Individualization, patient-centered discussion, and shared decision making should be utilized. In addition, ACOG has also released an update on different AFS modalities.

AFS Techniques

  • Maternal-Fetal Movement (kick counts)
    • Evidence does not currently support clinical utility of this approach
    • May be associated with increased harms due to unnecessary interventions
  • Contraction Stress Test (CST)
    • IV oxytocin or nipple stimulation used to generate ≥3 contractions that persist for at least 40 seconds each in a 10-minute period
    • Interpretation based on presence or absence of late FHR deceleration
    • Considered to be “safe and effective method of investigating FHR nonreactivity in preterm gestations”
  • Nonstress Test (NST)
    • Based on fetal heart rate reactivity
    • Loss of reactivity can be associated with sleep cycle as well as CNS depression
    • Reactive: ≥2 FHR accelerations that peak at least 15 beats per minute above the baseline and last 15 seconds within a 20-minute period
      • May need to extend to ≥40 minutes due to fetal sleep–wake cycle variations
      • If <32 weeks, 10 beats per minute for at least 10 seconds due to increased risk for non-reactivity can be used to predict fetal well-being
  • Biophysical Profile (BPP)
    • Ultrasound examination with 4 components: Fetal breathing | Fetal movement | Fetal tone | AFV ≥2cm
    • Can include NST but may be omitted if other 4 categories are within normal
  • Modified BPP
    • Used in the late 2nd or 3rd trimester
    • Combines NST with AFV measurement

Note: Negative predictive value (based on incidence of stillbirth occurring within 1 week of a normal test) is high for NST (99.8%) and >99.9% for CST, BPP and modified BPP

INDICATIONS:

Fetal Factors

Fetal Growth Restriction (FGR)  

  • Normal or elevated UA doppler but diastolic flow present and no other concerning maternal or fetal conditions
    • Initiate AFS at diagnosis
    • Continue testing once or twice weekly
  • Absent end diastolic velocity (AEDV) or concurrent conditions
    • Initiate AFS at diagnosis
    • Continue testing twice weekly
  • Consider inpatient management for
    • AEDV or
    • Concurrent conditions or
    • Reversed end diastolic flow

Uncomplicated Twins

  • Dichorionic twins
    • 36w0d: Initiate weekly testing
  • Monochorionic-diamniotic twins
    • 32w0d: Initiate weekly testing

Complicated Twin Pregnancies (including Monoamniotic) or Higher Order Multiples

  • Individualize testing

Decreased Fetal Movements

  • Initiate AFS at time of diagnosis
    • Repeat if decreased movements recur

Maternal Factors

Hypertension and Diabetes

  • Chronic hypertension with medications
    • 32w0d: Initiate weekly testing
  • Poorly controlled or associated medical conditions
    • Individualize testing
  • Hypertensive disorders of pregnancy (gestational hypertension or preeclampsia)
    • Without severe features: Twice weekly from time of diagnosis
    • With severe features: Daily testing
  • Gestational Diabetes
    • Initiate at 32w0d
    • Controlled and no comorbidities: Once or twice weekly testing
    • Poorly controlled: Twice weekly testing
  • Pregestational Diabetes
    • Initiate at 32w0d
    • Twice weekly testing  

Systemic Lupus Erythematous, Antiphospholipid Syndrome, Sickle Cell Disease, Renal Disease or Thyroid Disorders

  • Initiate AFS for above disorders by 32w0d if uncomplicated
  • Systemic lupus erythematosus
    • Weekly testing | If complicated, individualize care beginning at time of diagnosis
  • Antiphospholipid Syndrome
    • Twice weekly testing
  • Sickle cell disease
    • Once or twice weekly testing | Weekly testing | If complicated, individualize care beginning at time of diagnosis
  • Renal disease (Cr >1.4 mg/dL)
    • Once or twice weekly testing
  • Thyroid disorders that are poorly controlled can be individualized

IVF

  • 36w0d: Initiate weekly testing

Substance Use

  • Alcohol 5+ drinks/week
    • 36w0d: Initiate weekly testing
  • Polysubstance abuse
    • individualize initiation and surveillance

Obesity

  • Prepregnancy BMI 35.0 to 39.9
    • 37w0d: Initiate weekly testing
  • Prepregnancy BMI > 40.0
    • 34w0d: Initiate weekly testing

Obstetric Factors

  • Previous stillbirth
    • Occurred at ≥32w0d: Initiate weekly or twice weekly testing at 32w0d
    • Occurred at <32w0d: individualize initiation and surveillance
  • Previous FGR or preeclampsia with consequent preterm delivery
    • 32w0d: Initiate weekly testing  
  • Cholestasis
    • Initiate once or twice weekly testing at time of diagnosis
  • Late term
    • 41w0d: Initiate once or twice weekly testing
  • Abnormal serum markers (PAPP-A ≤5th percentile (0.4 MoM) or second trimester inhibin ≥2.0 Mom
    • 36w0d: Initiate weekly testing 

Placental Factors

  • Chronic placental abruption
    • Initiate once or twice weekly testing at time of diagnosis
  • Umbilical cord abnormalities (velamentous cord insertion, single umbilical artery)
    • 36w0d: Initiate weekly testing 
    • Individualize for vasa previa

Fluid Abnormalities

  • Isolated Oligohydramnios (single deepest vertical pocket [DVP] <2cm)
    • Initiate once or twice weekly testing at time of diagnosis
  • Polyhydramnios (DVP ≥12cm or AFI ≥30cm)
    • 32w0d to 34w0d: Initiate once or twice weekly testing

KEY POINTS:

Other Potential Indications

  • Genetic: Fetal anomalies and aneuploidy
    • Associated increased risk for stillbirth
    • Requires individualized care and consultation with specialists
  • Congenital infection
    • Evidence does not support routine AFS for other congenital infections 
    • Parvovirus infection is an exception based on evidence that there is a role for serial ultrasonography and middle cerebral artery Doppler assessment
  • Maternal Age
    • Studies show increased risk for stillbirth with advancing age
    • In isolation, age remains a poor predictor for stillbirth
    • Without other risk factors “there is insufficient evidence to recommend routine antenatal fetal surveillance” for pregnant women ≥35 years
    • Individualize initiation and surveillance if there is cumulative risk based on other factors

Evidence That AFS Improves Perinatal Outcomes

  • High-quality evidence remains limited
  • The ACOG Practice Bulletin states

It is important to emphasize that the guidance offered in this Committee Opinion should be construed only as suggestions; this guidance should not be construed as mandates or as all encompassing

There is a paucity of evidence for the efficacy of antenatal fetal surveillance and for evidence-based recommendations on the timing and frequency of antenatal fetal surveillance; consequently, for most conditions, recommendations for antenatal fetal surveillance are largely based on expert consensus and relevant observational studies 

Learn More – Primary Sources:

ACOG Committee Opinion 828: Indications for Outpatient Antenatal Fetal Surveillance

ACOG Practice Bulletin: Antepartum Fetal Surveillance