Outcomes of fetuses with small head circumference on second‐trimester ultrasonography

Abstract

We examined the outcomes of pregnancies in which the fetal head circumference (HC) was below the 5(th) centile at the routine second-trimester scan. We retrospectively analysed outcomes of 18,377 women according to HC Z scores at second-trimester ultrasound examination between 2001 and 2008. We collected all major malformations, intrauterine deaths and other abnormal outcomes. Six hundred seventy-four fetuses (3.7%) had an HC below the 5(th) centile. Twenty-one major malformations were noted, consisting mainly of neurological abnormalities (3.1%). There were seven intra uterine fetal death (1.3%). Of all the fetuses, 26% were lost to follow-up. Outcome and neurological development was normal in 467 cases, based on neonatal examination and/or parent or general practitioner reports. Major abnormalities were noted in respectively 26.2%, 3.0% and 1.1% of fetuses with Z scores < -2.5, -2.5 to -2.0, and -2 to -1.645, compared with 0.3% of fetuses with normal HC (p < 10(-4)). A head circumference below the 5(th) centile at second-trimester scan is associated with various abnormalities, especially neurological disorders. The outcome was worse when the HC was smaller. An HC Z score below -2.5 was strongly associated with neurological and chromosomal abnormalities. Conversely, an HC Z score below -1.645 but above -2, excluding cases with prenatally diagnosed malformations, seems to be reassuring for favorable neonatal outcome.