Serial head ultrasound studies in preterm infants: How many normal studies does one infant need to exclude significant abnormalities?

Abstract

Objective: We hypothesized that preterm infants with two normal head ultrasound (HUS) screening studies ≥7 days apart would have subsequently normal follow-up studies. Population: We reviewed reports of all HUS studies performed in preterm infants ≤32 weeks gestation admitted to our nursery between January 1998 and July 2000. Setting: Regional perinatal referral center. Design: A normal HUS screening study was defined as either no findings; or grade I intraventricular hemorrhage (IVH) (Papile classification), germinal matrix irregular or cyst, or normal but equal ventricular size. An abnormal study was defined as any with IVH ≥grade II, periventricular leukomalicia (PVL), ventriculomegaly (VM), or perventricular echogenicity (PVE). Results: Of 98 infants, 92 infants (94%) who had two normal HUS studies ≥7 days apart had normal repeat studies subsequently, and six (6%) were abnormal. Four of the six abnormal infants were <25 weeks gestation at birth. One infant (27 weeks) became abnormal after culture-positive bacterial sepsis and necrotizing enterocolitis with bowel perforation requiring surgery. The remaining infant (29 weeks) had a question of PVE, an a normal repeat study. The positive predictive value for having a normal HUS after two previously normal studies ≥7 days apart was 94% with a specificity 86%. Conclusion: Stable premature infants ≥25 weeks gestation without intervening deterioration may not need repeat screening HUSs after having had two normal studies ↓ days apart. Unstable or extremely premature infants <25 weeks gestation may be subject to late severe IVH, VM, and PVL, and therefore need a repeat study before hospital discharge, even if two initial studies ↓ days apart were normal.