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.