Timing of delivery in isolated FGR
A complicating factor in diagnosing FGR is distinguishing between the pathologically growth-restricted fetus and the constitutionally small fetus. Antenatal testing and serial umbilical artery Doppler assessment should be done following diagnosis of FGR to monitor for evidence of fetal compromise until delivery is planned.
The current ACOG Practice Bulletin No. 204 and Committee Opinion No. 764 recommend delivery between 38 0/7 and 39 6/7 weeks in the setting of isolated FGR with reassuring fetal testing and umbilical artery Doppler assessment.To further refine this, the new recommendations use the growth percentiles. In cases of isolated FGR with EFW between the 3rd and 10th percentile in the setting of normal umbilical artery Doppler, delivery is recommended between 38 and 39 weeks’ gestation. In cases of isolated FGR with EFW of less than the 3rd percentile (severe FGR) in the setting of normal umbilical artery Doppler, delivery is recommended at 37 weeks.
Timing of delivery in complicated FGR
A normal umbilical artery Doppler reflects the low impedance that is necessary for continuous forward flow of blood to the fetus. Abnormal umbilical artery Doppler signifies aberrations of this low-pressure system that affect the amount of continuous forward flow during diastole of the cardiac cycle. With continued compromise, there is progression to absent end-diastolic velocity (AEDV) and, most concerning, reversed end-diastolic velocity (REDV).
Serial umbilical artery Doppler assessment should be done following diagnosis of FGR to monitor for progression that is associated with perinatal mortality, since intervention can be initiated in the form of delivery. Delivery at 37 weeks is recommended for FGR with elevated umbilical artery Doppler of greater than the 95th percentile for gestational age. For FGR with AEDV, delivery is recommended between 33 and 34 weeks of gestation and for FGR with REDV between 30 and 32 weeks, as the neonatal morbidity and mortality associated with continuing the pregnancy outweighs the risks of prematurity in this setting. Because of the abnormal placental-fetal circulation in FGR complicated by AEDV/REDV, there may be a higher likelihood of fetal intolerance of labor and cesarean delivery (CD) may be considered.
WHAT THIS EVIDENCE MEANS FOR PRACTICE
- Fetal growth restriction is now defined as EFW of less than the 10th percentile or AC of less than the 10th percentile.
- Evaluation of FGR includes detailed anatomic survey and consideration of genetic evaluation, but infection screening should be done only if the patient is at risk for infection.
- With reassuring antenatal testing and normal umbilical artery Doppler studies, delivery is recommended at 38 to 39 weeks for isolated FGR with EFW in the 3rd to 10th percentile and at 37 weeks for FGR with EFW of less than the 3rd percentile.
- Umbilical artery Doppler studies are used to decrease the risk of perinatal mortality and further guide timing of delivery
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