Gestational Ultrasound at 8 Months (32+ Weeks) Gestation
At 8 months gestation (approximately 32-36 weeks), ultrasound is primarily ordered to assess fetal well-being in high-risk pregnancies through evaluation of fetal growth, amniotic fluid volume, and Doppler studies—not for routine screening in low-risk pregnancies. 1
Primary Indications for Third-Trimester Ultrasound
High-Risk Pregnancy Surveillance
- Antenatal fetal testing is NOT recommended in low-risk pregnancies at this gestational age 1
- Women with high-risk factors for stillbirth should undergo antenatal fetal surveillance, which typically includes ultrasound assessment 1
- The optimal interval for testing in high-risk pregnancies has become weekly or twice-weekly as standard practice 1
Specific Clinical Scenarios Requiring Ultrasound at 32+ Weeks
Fetal Growth Restriction (FGR) Monitoring:
- Serial ultrasound evaluation of fetal growth should be performed at 2-week intervals once FGR is diagnosed 1
- When umbilical artery Doppler shows decreased end-diastolic velocity or severe FGR (estimated fetal weight <3rd percentile), weekly umbilical artery Doppler evaluation is recommended 1
- With absent end-diastolic velocity, Doppler assessment should be performed 2-3 times per week 1
Hypertensive Disorders/Preeclampsia:
- In confirmed preeclampsia where maternal condition allows pregnancy continuation, serial evaluation of fetal growth, amniotic fluid volume, and umbilical artery Doppler are recommended from 26 weeks' gestation until birth 1
- Fetal biometry should be assessed no more frequently than every 2 weeks 1
- If umbilical artery Doppler demonstrates increased resistance (pulsatility index >95th percentile), sonographic surveillance should increase to weekly intervals 1
Term and Post-Term Pregnancy Assessment:
- At term (37+ weeks), ultrasound with biophysical profile (BPP) is rated as "usually appropriate" (rating 8/9) for assessment of fetal well-being in high-risk scenarios 1
- Modified biophysical profile is an alternative to full BPP, though nonstress testing may be complementary in cases of IUGR or oligohydramnios 1
What Is Actually Assessed at This Gestational Age
Biophysical Profile Components:
- Fetal breathing movements
- Fetal body movements
- Fetal tone
- Amniotic fluid volume
- Nonstress test (when part of modified BPP) 1
Growth Assessment:
- Fetal biometry including biparietal diameter, head circumference, abdominal circumference, and femur length to calculate estimated fetal weight 1
- Evaluation for growth restriction or macrosomia 1
Doppler Velocimetry (in specific high-risk cases):
- Umbilical artery Doppler is rated as "may be appropriate" (rating 6/9) for fetal well-being assessment 1
- Umbilical artery Doppler is NOT a reliable screening technique for FGR but is useful once FGR is diagnosed 1
Critical Clinical Pitfalls
Avoid routine third-trimester ultrasound in low-risk pregnancies:
- Third-trimester routine screening has not shown evidence of improved antenatal, obstetric, or neonatal outcomes in low-risk pregnancies 2
- Routine antenatal testing cannot predict stillbirth related to acute changes in maternal-fetal status such as abruption or cord accident 1
Abnormal findings at term typically mandate delivery:
- In term pregnancies, abnormal antenatal test results (BPP ≤6, nonreactive NST with modified BPP, abnormal umbilical artery Doppler, oligohydramnios, or polyhydramnios) are usually an indication for delivery 1
- Although false-positive results occur, delivery for abnormal antenatal testing is warranted in term pregnancies 1
Timing considerations for delivery planning:
- Decisions on optimal timing of delivery need to be made individually and may require involvement of an experienced obstetrician or fetal medicine specialist, particularly in severe, preterm FGR 1
- In cases of absent end-diastolic flow, delivery should be considered no later than 34 weeks gestation 1
- In cases of reversed end-diastolic flow, delivery should be considered no later than 30 weeks gestation 1