What is the recommended management for a fetus with intrauterine growth restriction (IUGR) at 36 weeks gestation, with a cerebroplacental ratio (CPR) less than 1, but normal umbilical Doppler study and normal amniotic fluid index (AFI)?

Management of IUGR at 36 Weeks with CPR<1 and Normal Umbilical Doppler

Plan for delivery at 37 weeks of gestation with weekly surveillance until delivery. 1

Delivery Timing

Your case represents IUGR with normal umbilical artery Doppler but abnormal cerebroplacental ratio (CPR<1), indicating brain-sparing physiology at 36 weeks gestation.

• Deliver at 37 weeks based on the Society for Maternal-Fetal Medicine (SMFM) 2020 guidelines, which recommend delivery at 37 weeks for FGR with decreased diastolic flow (elevated resistance) in the umbilical artery or severe FGR with estimated fetal weight <3rd percentile (GRADE 1B). 1

• While the umbilical artery Doppler is technically "normal," the CPR<1 indicates cerebral vasodilation (brain-sparing effect), suggesting placental insufficiency and fetal adaptation to hypoxemia. 1

• Important caveat: The SMFM guidelines explicitly state that middle cerebral artery Doppler and CPR should NOT be used for routine clinical management decisions, as evidence does not show improved accuracy over umbilical artery Doppler alone (GRADE 2B). 1 However, the presence of brain-sparing at this gestational age warrants closer surveillance.

Surveillance Protocol Until Delivery

Umbilical Artery Doppler Monitoring

• Weekly umbilical artery Doppler assessment to monitor for deterioration, particularly development of absent or reversed end-diastolic velocity. 1

• If umbilical artery shows absent end-diastolic velocity (AEDV), increase Doppler assessment to 2-3 times per week and consider earlier delivery at 33-34 weeks. 1

Fetal Surveillance

• Weekly cardiotocography (NST/BPP) after viability for FGR without absent/reversed end-diastolic velocity. 1

• Monitor amniotic fluid index weekly, as oligohydramnios would warrant more intensive surveillance or earlier delivery. 1

Clinical Reasoning

The SMFM guidelines prioritize umbilical artery Doppler over CPR because:

• Multiple studies show CPR has variable sensitivity (66%) and specificity (85%) for adverse outcomes. 1

• Large systematic reviews found insufficient high-quality evidence and wide variations in CPR accuracy for predicting perinatal outcomes in FGR. 1

• Clinical trials demonstrating that CPR-guided management improves outcomes are lacking. 1

However, at 36 weeks with CPR<1, you are only 1 week away from the recommended 37-week delivery threshold for FGR with abnormal Doppler, making conservative management with close surveillance until 37 weeks the most prudent approach. 1

Mode of Delivery

• Vaginal delivery with continuous electronic fetal monitoring is appropriate if umbilical artery end-diastolic flow remains present. 2

• Cesarean delivery is not routinely indicated for FGR alone unless other obstetric indications arise or fetal intolerance of labor occurs. 1

Common Pitfalls to Avoid

• Do not delay delivery beyond 37 weeks in the setting of confirmed FGR, even with reassuring testing, as stillbirth risk increases. 1, 3

• Do not rely solely on CPR to guide delivery timing, as current guidelines do not support this practice. 1

• Do not miss progression to AEDV or REDV on serial Doppler studies, which would necessitate immediate delivery planning at earlier gestational ages (33-34 weeks for AEDV, 30-32 weeks for REDV). 1, 4