Neonatal morphometry. Relation to obstetric, pediatric, and menstrual estimates of gestational age.

OBJECTIVE: To determine gestational age-dependent neonatal morphometrics based on last menstrual periods (LMPs), Ballard examinations, and obstetric estimates of gestational age.

DESIGN, SETTING, AND PARTICIPANTS: Cross-sectional survey of 38,818 live-born neonates at a tertiary care center in Detroit, Mich.

SELECTION PROCEDURES: Consecutive sample of all viable, structurally normal, singleton neonates delivered at Hutzel Hospital from 1984 through 1991.

MEASUREMENTS/MAIN RESULTS: Neonatal weights, lengths, and head circumferences were recorded at birth. Gestational age-dependent morphometrics were based solely on LMPs and compared with those based on obstetric estimates (using LMPs corrected by fetal ultrasound). Ballard examination had an 85.4% concurrence (within 14 days) with obstetric estimates of gestational age, but only a 69.9% (P less than .0001) agreement with LMP. Dating only by LMP significantly overestimated the prevalence of prematurity (odds ratio [OR], 1.3; 99% confidence interval [CI], 1.3 to 1.4) and postmaturity (OR, 5.0; 99% CI, 4.6 to 5.4), distorting apparent growth patterns, especially for preterm neonates. In contrast to previous studies based solely on LMPs, morphometric measurements increased beyond 40 weeks when dated by obstetric estimates.

CONCLUSIONS: Gestational age-dependent neonatal morphometrics should not be based solely on LMPs.