Prenatal gender-customized head circumference nomograms result in reclassification of microcephaly and macrocephaly

BACKGROUND: Local and worldwide prenatal charts for estimated fetal weight and postnatal charts for head circumference are gender specific. However, prenatal head circumference nomograms are not gender customized. OBJECTIVE: This study aimed to create gender-customized curves to assess between-gender head circumference differences and to study the clinical significance of using such gender-customized curves. STUDY DESIGN: A single-center retrospective study was conducted between June 2012 and December 2020. Prenatal head circumference measurements were obtained from routine estimated fetal weight ultrasound scans. Postnatal head circumference measurement at birth and gender were retrieved from computerized neonatal files. Head circumference curves were created, and the normal range was defined for the male and female subpopulations. After applying gender-specific curves, we analyzed the outcome of cases classified as microcephaly and macrocephaly according to non–gender-customized curves, which were reclassified as normal according to gender-specific curves. For these cases, clinical information and postnatal long-term outcomes were retrieved from patients’ medical records. RESULTS: The cohort included 11,404 participants (6000 males and 5404 females). The curve for male head circumference was significantly higher than the female curve for all gestational weeks (P<.0001). Applying gender customized curves resulted in fewer cases of male fetuses defined as 2 standard deviations above the normal range and female fetuses defined as 2 standard deviations below of the normal range. Cases reclassified as normal head circumference after the application of gender-customized curves were not related to increased adverse postnatal outcomes. The rate of neurocognitive phenotypes was not higher than the expected rate in both male and female cohorts. Polyhydramnios and gestational diabetes mellitus were more common in the normalized male cohort, whereas oligohydramnios, fetal growth restriction, and cesarean delivery were more common in the normalized female cohort. CONCLUSION: Prenatal gender-customized curves for head circumference can reduce the overdiagnosis of microcephaly in females and macrocephaly in males. According to our results, gender-customized curves did not affect the clinical yield of prenatal measurements. Therefore, we suggest that gender-specific curves be used to avoid unnecessary workup and parental anxiety.