Committee Opinion No 700: Methods for Estimating the Due Date

Purpose Heterogeneous findings exist on antiretroviral treatment (ART) use in pregnancy and preterm delivery (PTD) or infants born small-for-gestational age (SGA). Whether reported differences may be explained by methods used to ascertain gestational age(GA) has not been explored. Methods We enrolled consecutive pregnant women attending a large primary care antenatal clinic in South Africa. Public-sector midwives assessed GA by last menstrual period (LMP) and symphysis-fundal height (SFH). Separately, if clinical GA was <24weeks, ultrasound (US) was performed by a research sonographer blinded to midwife assessments. In analysis, the impact of measurement error on the association between HIV/ART status and birth outcome by GA method was assessed, and factors associated with clinical GA under- or over-estimation identified. Results In 1787 women included overall, estimated PTD incidence was 36% by LMP, 17% by SFH and 11% by US. PTD risk was higher for HIV-infected than HIV-uninfected women using US-GA (adjusted odds ratio (aOR) 1.95; 95% CI 1.10–3.46); for LMP/SFH-GA the associations were smaller and not significant. These findings persisted after adjustment for age, parity, height and previous PTD. PTD risk did not vary by timing of ART initiation (before or during pregnancy) for any method. Elevated BMI and older age were associated with decreased risk of under-estimation by both LMP and SFH; HIV status and obesity were associated with increased risk of over-estimation by SFH. There were no differences in SGA incidence across GA methods. Conclusions Findings for an association between HIV/ART and birth outcomes are substantially influenced by GA assessment method. With growing public health interest in this association, future research efforts should seek to standardize optimal measures of gestation.

Objective To compare the accuracy of a new formula to one developed in 1984 (and still in common use) and to develop and compare racial and ethnic–specific and racial and ethnic–neutral formulas. Methods The Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD)Fetal Growth Studies-Singletons was a prospective cohort study that recruited women in four self-reported racial–ethnic groups—Non-Hispanic Black, Hispanic, Non-Hispanic White, and Asian—with singleton gestations from 12 U.S. centers (2009–2013). Women with a certain last menstrual period confirmed by first-trimester ultrasonogram had longitudinal fetal measurements by credentialed study ultrasonographers blinded to the gestational age at their five follow-up visits. Regression analyses were performed with linear mixed models to develop gestational age estimating formulas. Repeated cross-validation was used for validation. The estimation error was defined as the mean squared difference between the estimated and observed gestational age and was used to compare the formulas’ accuracy. Results The new formula estimated the gestational age (± 2 standard deviations) within ±7 days from 14–20 weeks, ±10 days from 21–27 weeks and ±17 days from 28–40 weeks. The new formula performed significantly better than a formula developed in 1984 with an estimation error of 10.4 versus 11.2 days from 21–27 weeks, and 17.0 versus 19.8 days at 28–40 weeks, respectively. Racial and ethnic–specific formulas did not outperform the racial and ethnic–neutral formula. Conclusions The NICHD gestational age estimation formula is associated with smaller errors than a well-established historical formula. Racial and ethnic–specific formulas are not superior to a racial–ethnic neutral one.

IMPORTANCEData on birth outcomes and early mortality are scarce, especially in settings with limited resources. Total births, both stillbirths and live births, are often not counted, yet such data are critical to allocate resources and target interventions to improve survival. OBJECTIVE To estimate the prevalence of stillbirths, neonatal deaths, and medically vulnerable phenotypes, such as preterm births, small-for-gestational-age (SGA), large-for-gestational-age (LGA), and low-birth-weight (LBW) births, in a setting where these key indicators remain largely unknown.