While 2020 was a challenge to say the least, obstetrician-gynecologists remained on the frontline caring for women through it all. Life continued despite the COVID-19 pandemic: prenatal care was delivered, albeit at times in different ways; babies were born; and our role in improving outcomes for women and their children became even more important. This year’s Update focuses on clinical guidelines centered on safety and optimal outcomes for women and children.
ACOG and SMFM update guidance on FGR management
American College of Obstetricians and Gynecologists. Practice advisory: Updated guidance regarding fetal growth restriction. September 2020. https://www.acog.org/clinical/clinical-guidance/practice-advisory/articles/2020/09/updated-guidance-regarding-fetal-growth-restriction. Accessed December 18, 2020.
Fetal growth restriction (FGR) affects up to 10% of pregnancies and is a leading cause of infant morbidity and mortality. Suboptimal fetal growth can have lasting negative effects on development into early childhood and, some hypothesize, even into adulthood.1,2 Antenatal detection of fetuses with FGR is critical so that antenatal testing can be implemented in an attempt to deliver improved clinical outcomes. FGR is defined by several different diagnostic criteria, and many studies have been conducted to determine how best to diagnose this condition.
In September 2020, the American College of Obstetricians and Gynecologists (ACOG) released a Practice Advisory regarding guidance on FGR in an effort to align the ACOG Practice Bulletin No. 204, ACOG Committee Opinion No. 764, and SMFM (Society for Maternal-Fetal Medicine) Consult Series No. 52.3-5 This guidance updates and replaces prior guidelines, with an emphasis on 3 notable changes.
FGR definition, workup have changed
While the original definition of FGR was an estimated fetal weight (EFW) of less than the 10th percentile for gestational age, a similar level of accuracy in prediction of subsequent small for gestational age (SGA) at birth has been shown when this or an abdominal circumference (AC) of less than the 10th percentile is used. Based on these findings, SMFM now recommends that FGR be defined as an EFW or AC of less than the 10th percentile for gestational age.
Recent studies have done head-to-head comparisons of different methods of estimating fetal weight to determine the best detection and pregnancy outcome improvement in FGR. In all instances, the Hadlock formula has continued to more accurately estimate fetal weight, prediction of SGA, and composite neonatal morbidity. As such, new guidelines recommend that population-based fetal growth references (that is, the Hadlock formula) should be used to determine ultrasonography-derived fetal weight percentiles.
The new guidance also suggests classification of FGR based on gestational age at onset, with early FGR at less than 32 weeks and late FGR at 32 or more weeks. The definition of severe FGR is reserved for fetuses with an EFW of less than the 3rd percentile. A diagnosis of FGR should prompt the recommendation for a detailed obstetric ultrasonography. Diagnostic genetic testing should be offered in cases of early-onset FGR, concomitant sonographic abnormalities, and/or polyhydramnios. Routine serum screening for toxoplasmosis, rubella, herpes, or cytomegalovirus (CMV) should not be done unless there are risk factors for infection. If amniocentesis is performed for genetic diagnostic testing, consideration can be made for polymerase chain reaction for CMV in the amniotic fluid.
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