280: “Microcephaly” at birth: What can we learn from prenatal ultrasound patterns?

Abstract

We sought to determine whether the trajectory of prenatal ultrasound head circumference (HC) in the third trimester could infer etiology for newborns with microcephaly at birth. Retrospective database review of neonates with microcephaly with ≥2 3rd trimester ultrasounds at our institution from 12/1/2005 - 12/31/2015. Included patients were those who delivered at our institution and had prenatal ultrasound data, gestational age (GA) at delivery, HC and weight measurements. Microcpehaly was defined as birth HC <3%ile using the Fenton calculator. Potential etiologies evaluated were genetic, prenatal intrauterine growth restriction (IUGR), infectious and hypertensive disorders of pregnancy (HTN), defined as a diagnosis of chronic hypertension and/or preeclampsia. If none of these were found, the cause was labeled “idiopathic”. Data was converted to Z scores based on the mean and SD of our population 11,134 newborns met inclusion criteria. Of these, 152 (1.4%) had HC<3% at birth, and 56 (36.8%) had HC <3% at birth and ≥ 2 ultrasounds at ≥ 26 weeks. Of these, 6 (11%) were in HTN group, 22(39.3%) were in the IUGR group and did not have HTN, 1 (2%) was aneuploid, and 28 (50.0%) were idiopathic. At the earliest 3rd trimester ultrasound, the HC in the IUGR group was smaller than HC in the idiopathic group (z-score =1.4 vs -0.5, p = .002) but not significantly different from the HTN group (z-score =-0.5, p = .081). When comparing HC growth trajectories, the HTN and idiopathic groups demonstrated decreasing HC over time and the IUGR group HC growth was more stable. Comments about a small HC were made in the charts of 5 (8.9%) newborns, and by the first week of life. Only 2 (3.6%) babies, both in the IUGR group, underwent postnatal evaluation for microcephaly. Compared to the HTN and idiopathic groups, the HCs of patients in the IUGR group were noted to be smaller earlier in gestation, but exhibited a more stable growth trajectory over time. This may be due to a deleterious event early in gestation causing the head to be small early on, but maintain stable growth. This is in contrast to the HTN and idiopathic groups, where there was a sharper drop off of HC growth over time, which is consistent with the growth pattern seen with placental insufficiency. Future studies will focus on HC growth trajectory over the first few years of life in those diagnosed with microcephaly at birth.