At what gestational age should a biophysical profile ideally be started in a low-risk pregnancy versus a high-risk pregnancy?

Timing of Biophysical Profile Initiation

For high-risk pregnancies, biophysical profile (BPP) testing should begin at 26-28 weeks of gestation when fetal growth restriction (FGR) is identified or suspected, with testing frequency of at least weekly for normal results and twice weekly or more frequently for abnormal findings; for low-risk pregnancies, routine BPP is not recommended at any gestational age. 1, 2

High-Risk Pregnancy Protocol

When to Start BPP

• Initiate BPP at 26-28 weeks of gestation in high-risk pregnancies once FGR is diagnosed or when the fetus reaches the point of potential viability 1, 2
• The BPP becomes indispensable for assessment of fetal well-being once FGR is identified, as it evaluates four parameters sensitive to fetal hypoxemia: fetal breathing movements, limb/body movements, fetal tone, and amniotic fluid volume 1
• For pregnancies at risk for fetal demise, testing should evaluate one or more fetal well-being parameters from the point of postnatal viability until delivery is indicated 1

Testing Frequency Based on Risk Level

• Weekly testing is standard for high-risk pregnancies with normal BPP results 1
• Twice weekly testing is indicated for fetuses at highest risk for fetal demise or when abnormal umbilical artery Doppler is detected 1
• Daily or more frequent testing may be indicated in critical situations, such as when reversed end-diastolic velocity is detected 1

Specific High-Risk Conditions Requiring BPP

• Confirmed FGR with estimated fetal weight <10th percentile warrants BPP initiation regardless of Doppler findings 1
• Preeclampsia diagnosis requires immediate fetal biometry, amniotic fluid assessment, and serial surveillance from 26 weeks if pregnancy continuation is planned 2
• Monochorionic twin pregnancies require surveillance beginning at 16-20 weeks for twin-twin transfusion syndrome screening, though full BPP is typically reserved for later gestational ages 1, 2

Low-Risk Pregnancy Guidance

• BPP is not recommended for routine antenatal testing in low-risk pregnancies at any gestational age 1
• There is no convincing evidence that routine antenatal testing in low-risk pregnancies improves perinatal outcome, and false-positive results may lead to unnecessary interventions including increased cesarean delivery rates 1
• A Cochrane review of randomized controlled trials found insufficient evidence to support BPP use even in high-risk pregnancies, though guideline consensus supports its use in this population 3

Critical Timing Considerations

Gestational Age Limitations

• Before 24 weeks, detailed Doppler assessment and comprehensive fetal surveillance have unacceptable accuracy, sensitivity, and positive predictive values 2
• At 20-24 weeks (periviable period), BPP completion requires extended observation time of approximately 23 minutes (versus 9 minutes in term pregnancies) to achieve a score of 8/8, with 97% success rate when extended to 44 minutes 4
• After 32 weeks, the risk of fetal demise decreases even among uncomplicated monochorionic twins, though surveillance should continue until delivery 1

Integration with Doppler Studies

• Umbilical artery Doppler should be initiated at 26-28 weeks in high-risk pregnancies and performed every 2 weeks if normal 1, 2
• When decreased end-diastolic velocity is detected, increase to weekly Doppler assessment 1, 2
• When absent end-diastolic velocity is present, perform Doppler 2-3 times per week and consider delivery at 33-34 weeks 1, 2, 5
• Reversed end-diastolic velocity mandates hospitalization with cardiotocography 1-2 times daily and Doppler assessment 3 times weekly, with delivery consideration at 30-32 weeks 2, 5

Common Pitfalls to Avoid

• Do not delay BPP initiation once FGR is suspected, as umbilical artery Doppler incorporated into management reduces perinatal death by 38% in high-risk pregnancies 1, 2
• Do not rely on BPP as a screening tool for detecting FGR—it is a surveillance tool for assessing fetal well-being once FGR is already identified 1
• Do not use standard 30-minute observation time for periviable pregnancies (20-24 weeks), as these fetuses require up to 44 minutes to achieve a normal score of 8/8 4
• Do not perform BPP in isolation—it should be coupled with umbilical artery Doppler assessment, as Doppler provides complementary information about placental function 1

Scoring and Clinical Action

• Each of the four BPP components receives a score of 0 or 2, with a maximum score of 8 (or 10 when nonstress test is included) 1
• Scores of 8 or 10 are strong indicators of a well-compensated fetus 1
• Amniotic fluid volume should be assessed at least weekly but may require more frequent evaluation if approaching abnormally low levels 1
• The modified BPP (nonstress test plus amniotic fluid index) is an acceptable alternative to full BPP, though nonstress test may be complementary in cases of FGR or oligohydramnios 1