Fetal Growth Restriction

Fetal Growth Restriction (FGR) has been identified as a critical opportunity for reducing poor pregnancy outcomes including stillbirth, preterm birth, prolonged neonatal hospitalization, and developmental delays. Undetected FGR has an 8-fold increased risk for stillbirth over detected FGR.

Fundal height measurement has shown to have mixed results in identifying growth restriction, yet serial ultrasound is not recommended as a screening tool for all pregnancies. Therefore, the recommended care plan focuses on screening all pregnancies for risk factors and ensuring those with any high-risk factors or multiple moderate risk factors are referred for additional assessment and surveillance. Both Symphysis-Fundal Height (SFH) and Estimated Fetal Weight (EFW) measurements should be tracked on growth charts beginning by 20 weeks. One limitation of current guidelines is that they are based on the EFW which indicates size, not growth. This increases the chances of missing larger babies that are not meeting their growth potential, but also risks inappropriately diagnosing constitutionally small babies as growth restricted. Serial measurements offer an opportunity to reduce false negatives and identify babies at risk for poor outcomes.

Timing of delivery when FGR is present is determined by a combination of results from maternal health status, non-stress test (NST), biophysical profile (BPP), amniotic fluid index (AFI), Doppler studies, and other tests as indicated. All pregnancies complicated by growth restriction should be delivered by 39 weeks.

Background

FGR complicates 5-10% of all pregnancies and is the biggest known risk factor for stillbirth. It is also associated with premature birth, intrapartum hypoxia, prolonged neonatal hospitalization, feeding and respiratory difficulties, abnormal brain development, long-term cardiovascular disease, developmental delays, and early mortality. When unrecognized, FGR is associated with an 8x increased risk of stillbirth compared to non-FGR pregnancies. Improving the identification of FGR plus surveillance and timely delivery is associated with a decrease in stillbirth.

The most common cause of FGR is placental insufficiency. Other causes include maternal health conditions associated with vascular disease, fetal chromosomal abnormalities, and cord and placenta abnormalities (placental abruption, circumvallate placenta, hemangioma, chorioangioma, velamentous or marginal cord insertion, two-vessel cord). In FGR, small arteries in the placental villi are damaged or destroyed causing a progressive decrease in end-diastolic blood flow in the umbilical artery until it is absent and then reversed. Early onset FGR (diagnosed before 32 weeks) has the largest impact on nutrition and growth, while late onset FGR (32 weeks or later) impacts respiratory demands.

Screening

All pregnancies should be screened for FGR with SFH. Ultrasound screening should be used if there are risk factors for FGR present or the mother has a BMI greater than 35, polyhydramnios, or large fibroids. During the fetal anatomic ultrasound in the second trimester, the presence of fetal biometry measurements more
than one week behind gestational age, short femur, echogenic bowel, two-vessel cord, or a marginal or velamentous cord insertion may be early indicators of fetal growth restriction. The combination of screening for risk factors and fetal biometry has been shown to identify more than 90% of FGR pregnancies at 30-34 weeks gestation. PAPP-A and PlGF may also be used to identify pregnancies at risk.

Diagnosis

Assessment for FGR should include a detailed history, screening for congenital infections, and detailed ultrasound. PlGF or sFlt1/PlGF ratio should be added if being done after 24 weeks gestation. Genetic consultation and amniocentesis should be offered if before 32 weeks, especially if accompanied by structural abnormalities, polyhydramnios, or soft markers.

Early onset FGR is diagnosed before 32 weeks and requires at least one of three criteria to be present:

• Abdominal circumference or EFW below the 3rd percentile
• Late changes in the umbilical artery Doppler assessment
• Fetal abdominal circumference or EFW below the 10th percentile accompanied by abnormal uterine artery Doppler study (mean pulsatility index >95th percentile) or abnormal umbilical artery Doppler study (pulsatility index >95th percentile)

Late onset FGR is diagnosed at or after 32 weeks with abdominal circumference or EFW below the 3rd percentile, OR two of the following criteria:

• Abdominal circumference or EFW below the 10th percentile
• Abdominal circumference or EFW crossing 2 quartiles
• Abnormal Doppler finding (umbilical artery Doppler pulsatility index above the 95th percentile or a cerebroplacental ratio below the 5th percentile)

Management

See Appendix A for recommended algorithms for screening and management of FGR. In early onset FGR, a combination of serial ultrasounds and Doppler studies should be used for monitoring. In late onset FGR, additional tools include maternal monitoring of fetal movements and weekly biophysical profiles and NSTs. Aspirin decreases the risk of preeclampsia and SGA in high risk women. Nutritional supplements and maternal hyperoxygenation have not been shown to be effective. Admission for in-patient monitoring is appropriate in the presence of reversed

EDV or when other complications such as preeclampsia or insulin-dependent diabetes exist. Indications for immediate delivery include severe preeclampsia, HELLP syndrome, placental abruption, or NST abnormalities. The risk of stillbirth outweighs the risk of neonatal morbidity and mortality at 33-34 weeks if the umbilical artery EDV is absent. This ratio is moved to 30 weeks if the umbilical artery EDV is reversed, or the ductus venosus EDV is absent or reversed. Cesarean delivery is recommended for placenta-mediated, early-onset FGR and major Doppler abnormalities to avoid fetal compromise during labor. A consultation with a neonatologist is recommended if early delivery is a possibility.

Late-onset FGR with abnormal umbilical artery Doppler studies, abnormal cerebroplacental ratio, abnormal BPP, oligohydramnios, or concurrent diagnosis of preeclampsia should be considered for delivery by 37 weeks. In mild FGR with normal Doppler studies and AFI, delivery between 37 and 39 weeks is recommended.

Recommendations

• Determine and document EDD ASAP to increase accuracy for percentile measurements
• Screen all pregnancies for risk factors
• Start aspirin 100mg qd by 16 weeks for high risk of hypertensive disorders of pregnancy until delivery
• Start uterine artery Dopplers at 20 weeks if 2 or more moderate risk factors for FGR
• Start fundal height measurements at 20 weeks, repeat every 2 weeks
• Screen pregnancies with a risk factor for FGR at 32 weeks with ultrasound EFW
• Use serial U/S instead of fundal height for screening if the pregnancy is complicated by uterine fibroids, high maternal BMI, polyhydramnios, positive screening tests for SGA, fundal height more than 3 cm of discrepancy with gestation
• Plot all fundal height measurements and EFWs on growth charts
• If EFW 10th – 20th percentile and fractional thigh volume is < 10th volume is 10-20th percentile, use short-interval follow up or consider surveillance if other clinical factors present
• If fundal height is less than 10th percentile, static growth, or change in rate of growth (more than 30 percentiles in EFW or AC over 8 weeks), proceed to U/S, AFI, NST, Doppler, and PlGF.
• If U/S confirms SGA, proceed to Doppler studies, serial biometry, amniotic fluid volume, NST, and BPP every 2 weeks. OBs and midwives consult with and/or refer to MFM
• If FGR diagnosis before 32 weeks or is present with polyhydramnios or fetal malformation, offer prenatal diagnostic testing and genetic counseling
• If FGR with FHR decelerations – immediate delivery by c/section
• If FGR with reversed EDV of umbilical artery or ductus venosus PI >95th percentile, deliver by 30 weeks
• If FGR – deliver at 34 0/7 – 37 6/7 if also has oligohydramnios, abnormal Doppler studies, maternal risk factors, or other comorbidities
• If FGR – deliver at 37 weeks
• If severe FGR (EFW less than 3rd percentile) – deliver at 37 0/7
• If early FGR – deliver at any gestation if maternal indication (ie HELLP); at 26+0 if repeated and persistent FHR decels or BPP <4; at 26+0 – 28+6
• If ductus venosus below baseline or cCTG STV <2.6ms; at 29+0 – 31+6 if ductus venosus below baseline or cCTG STV < 3.0ms; at 23+0 – 33+6 if umbilical artery EDF is reversed or cCTG STV <3.5ms; at 34+0 if umbilical artery EDF is absent or cCTG STV <4.5ms
• Consider elective c/section for early FGR if abnormal cCTG STV, abnormal ductus venosus Doppler, absent or reversed umbilical artery EDF, abnormal BPP, or maternal indication
• If late FGR: deliver immediately if repeated and persistent FHR decels, BPP <4, maternal indication, absent or reversed umbilical artery EDF, or cCTG STV <3.5ms (before 34 weeks) or <4.5ms (after 34 weeks); deliver at 36+0 – 37+6 if umbilical artery PI >95th percentile or AC/EFW < 3rd percentile; at 38+0 – 39+0 if evidence of cerebral blood flow redistribution or any other feature of FGR. Deliver all FGR pregnancies by 37-38 weeks
• Delivery recommendations
  • 24-26 weeks – deliver for maternal indications
  • 26-28 weeks – deliver if BPP <6/10
  • 28-32 weeks – delivery if DV reversed
  • 32-34 weeks – deliver if reversed UA EDV
  • 34-38 weeks – deliver if absence of UA EDV or consider MCA results
  • 38+ weeks – deliver
• Conduct chart audits to identify missed FGR