SAN DIEGO – Fetal growth ultrasound does not identify fetuses destined to be small for gestational age at birth, but it does identify fetuses with increased risk of significant morbidity and mortality in the postnatal period.
Those are key findings from a large retrospective study presented by Dr. Jacob C. Larkin at the annual Pregnancy Meeting sponsored by the Society for Maternal-Fetal Medicine.
Dr. Jacob C. Larkin
“Small for gestational age (SGA) newborns and fetuses are known to be at increased risk of stillbirth, neonatal morbidity and mortality, and adult disease,” Dr. Larkin said in an interview in advance of the meeting. “We show that ultrasound is not a good tool for identifying fetuses that are destined to be SGA at birth. However, for those babies that are SGA when they’re born (the smaller 10% of newborns) fetal growth ultrasound appears to be an effective tool for stratifying risk in the neonatal period.”
In a study led by Dr. Larkin of the division of maternal-fetal medicine in the department of obstetrics, gynecology, and reproductive sciences at the University of Pittsburgh, researchers retrospectively evaluated 125,069 nonanomalous singletons, delivered beyond 24 weeks at the university’s Magee-Womens Hospital between 1995 and 2011. Using Alexander’s nomogram, newborns were classified as appropriate for gestational age (AGA; weight at 10%-89% for GA) or SGA, which were categorized into three groups: no growth ultrasound (US) in third trimester; US in the third trimester but no diagnosis of fetal growth restriction (FGR); and diagnosed as FGR antenatally. An Apgar score of less than 4 at 5 minutes and neonatal mortality were adjusted for nulliparity, maternal education, tobacco use, race, marital status, and neonatal gender.
Of the 125,069 newborns evaluated, 10% (12,474) were SGA. Of these, 81% (10,140) did not have US after 24 weeks, a finding that surprised Dr. Larkin. Of those 2,334 SGA who had a growth US, 81% were not identified as FGR. Overall, only 3% (431) of SGA were detected antenatally as FGR. SGA newborns who were found to have an estimated fetal weight below the 10th percentile, and thus labeled as growth restricted, were at significantly increased risk of neonatal death (adjusted odds ratio, 15.39). On the other hand, newborns with birth weights below the 10th percentile who had an ultrasound before birth that found them to be appropriately grown were at no greater risk of neonatal death or low Apgar score than were newborns with normal birth weights (aOR, 1.19 and 1.34, respectively).
A key strength of the study, Dr. Larkin said, was its large sample size and the fact that US data was linked to neonatal outcomes. Limitations of the study include the absence of stillbirths in the cohort. “Also, the data used was not collected as part of a protocol, and all ultrasounds were obtained for clinical indications, which makes it difficult to compare outcomes in patient that had ultrasound and those that didn’t without bias,” he said.
Dr. Larkin reported having no relevant financial conflicts.
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