Contributor: Eric Dellinger, MD
Last Update: 11/1/2010
The cornerstone of diagnosis is an accurate EDC. Stringently review the criteria for assigning the EDC. In the protocol “Determining the EDC from Ultrasound” we find the following guidelines:
- At less than 12 weeks, the CRL should agree with LMP +/- 5 days.
- At 12-20 weeks, the composite measurements should agree +/- 8 days.
- At 20-30 weeks, the composite measurements should agree +/- 14 days.
- At >30 weeks, the composite measurements should agree +/- 21 days.
- Evaluation of the TCD can be helpful late in pregnancy since it tends to be less affected by alterations in abnormal fetal growth. Work by Chavez et al on over 24,000 TCD data points has generated a nomogram. Concordance between the actual and predicted gestational age was high (r = 0.92; P < .0001). Between 17 and 21 weeks, and between 22 and 28 weeks of gestation, the predicted gestational age ranged between 0 and 4 days, and between 0 and 2 days, respectively, of actual gestational age. Between 29 and 36 weeks of gestation, predicted gestational age was within 5 days of actual gestational age; at 37 weeks of gestation, the predicted gestational age was discrepant by 9 days.
If fundal height assessment detects a lag of 3 cm or more, obtain a sonogram to assess fetal growth and amniotic fluid volume. The clinical value of fundal heights beyond 32 weeks is questionable. Low risk patients who have experienced lightening may not warrant further evaluation.
FGR is defined as an estimated fetal weight below the 10th percentile for a given gestational age. The HC/AC ratio can assist in labeling FGR as symmetric versus asymmetric. Other sonographic findings worthy of comment include AC measurements below the 5th percentile, oligohydramnios, and abnormal Doppler studies.
Once the diagnosis of FGR is made, institute twice weekly fetal surveillance as well as weekly amniotic fluid volume and Doppler assessment. At least one study has demonstrated a reduction in stillbirth when using twice weekly versus weekly testing in cases of FGR. Monitor interval growth every 2-3 weeks. Initiate a fetal movement protocol in the outpatient setting.
Regarding cases where the EFW is in the normal range, but the AC lies below the 5th percentile, additional surveillance may be beneficial. Interval fetal growth assessment should be obtained at 2-3 week intervals. If a small AC (<5th percentile), coexisting oligohydramnios or abnormal Dopplers are found, extend the diagnosis of FGR restriction and begin a twice weekly fetal testing protocol.
If subsequent studies demonstrate normalization of fetal growth, fluid, and Dopplers where they were previously abnormal, further fetal testing may not be indicated if the pregnancy is free from factors known to be high risk for abnormal placental perfusion and FGR. Such cases need to be managed on an individualized basis.
Early onset FGR may represent a different etiology other than placental insufficiency. In particular, second trimester FGR has been associated with fetal aneuploidy, genetic syndromes, anomalies, and fetal infections such as CMV and toxoplasmosis. A fetal karyotype, amniotic fluid cultures, and ToRCH titers may be indicated for cases of FGR seen as early as the second trimester. The ultrasound findings of anomalies or calcifications within the placenta, fetal brain and liver, may point to one of these causes.
Doppler measurements have shown some promise in the monitoring of pregnancies complicated by FGR. Doppler of the umbilical arteries is thought to reflect placental health and abnormally high indices can suggest restricted flow through the placenta. Doppler measurements of the middle cerebral arteries can detect adaptive shunting of blood to the fetal brain. Lastly, Doppler flow studies of the fetal ductus venosus can possibly indicate cardiac decompensation and in some studies have allowed better timing of delivery of the severely preterm and growth restricted fetus, especially those with absent or reversed end diastolic velocities of the umbilical artery. Conversely, completely normal Doppler studies may constitutional FGR as the etiology of a large number of fetuses with estimated weights below the 10th percentile.
Timing of Delivery
In most cases, pregnancy can be continued until term. Factors which might favor an earlier delivery include severe FGR (EFW < 5th percentile), oligohydramnios, abnormal Doppler studies, decreased fetal movement, abnormal fetal reassurance testing, or coexisting morbidities. Amniocentesis has a role in safely allowing early delivery in some cases of FGR. Liberal use of labor induction at 39 completed weeks of more, especially in patients with a favorable Bishop’s score, is also reasonable. However, awaiting the onset of spontaneous labor will likely improve the chance of a vaginal delivery.
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