Comparison of gestational weight gain z-scores and traditional weight gain measures in relation to perinatal outcomes.

BACKGROUND: Conventional measures of gestational weight gain (GWG) are correlated with pregnancy duration, and may induce bias to studies of GWG and perinatal outcomes. A maternal weight-gain-for-gestational-age z-score chart is a new tool that allows total GWG to be classified as a standardised z-score that is independent of gestational duration. Our objective was to compare associations with perinatal outcomes when GWG was assessed using gestational age-standardised z-scores and conventional GWG measures. METHODS: We studied normal-weight (n=522 120) and overweight (n=237 923) women who delivered liveborn, singleton infants in Pennsylvania, 2003-11. GWG was expressed using gestational age-standardised z-scores and three traditional measures: total GWG (kg), rate of GWG (kg per week of gestation), and the GWG adequacy ratio (observed GWG/GWG recommended by the Institute of Medicine). Log-binomial regression models were used to assess associations between GWG and preterm birth, and small- and large-for-gestational-age births, while adjusting for race/ethnicity, education, smoking, and other confounders. RESULTS: The association between GWG z-score and preterm birth was approximately U-shaped. The risk of preterm birth associated with weight gain <10th percentile of each measure was substantially overestimated when GWG was classified using total kilogram and was moderately overestimated using rate of GWG or GWG adequacy ratio. All GWG measures had similar associations with small- or large-for-gestational-age birth. CONCLUSIONS: Our findings suggest that studies of gestational age-dependent outcomes misspecify associations if total GWG, rate of GWG, or GWG adequacy ratio are used. The potential for gestational age-related bias can be eliminated by using z-score charts to classify total GWG.

Validity of birth certificate-derived maternal weight data.

BACKGROUND: Studies using vital records-based maternal weight data have become more common, but the validity of these data is uncertain. METHODS: We evaluated the accuracy of prepregnancy body mass index (BMI) and gestational weight gain (GWG) reported on birth certificates using medical record data in 1204 births at a teaching hospital in Pennsylvania from 2003 to 2010. Deliveries at this hospital were representative of births statewide with respect to BMI, GWG, race/ethnicity, and preterm birth. Forty-eight strata were created by simultaneous stratification on prepregnancy BMI (underweight, normal weight/overweight, obese class 1, obese classes 2 and 3), GWG (<20th, 20-80th, >80th percentile), race/ethnicity (non-Hispanic white, non-Hispanic black), and gestational age (term, preterm). RESULTS: The agreement of birth certificate-derived prepregnancy BMI category with medical record BMI category was highest in the normal weight/overweight and obese class 2 and 3 groups. Agreement varied from 52% to 100% across racial/ethnic and gestational age strata. GWG category from the birth registry agreed with medical records for 41-83% of deliveries, and agreement tended to be the poorest for very low and very high GWG. The misclassification of GWG was driven by errors in reported prepregnancy weight rather than maternal weight at delivery, and its magnitude depended on prepregnancy BMI category and gestational age at delivery. CONCLUSIONS: Maternal weight data, particularly at the extremes, are poorly reported on birth certificates. Investigators should devote resources to well-designed validation studies, the results of which can be used to adjust for measurement errors by bias analysis.

Pregnancy glycemia in Mexican-American women without diabetes or gestational diabetes and programming for childhood obesity.

In the present study, we estimated the association between pregnancy glucose levels and offspring body mass index (BMI) z scores at 2, 3.5, 5, and 7 years of age, as well as z score trajectories across this age range, among Mexican-American women without diabetes or gestational diabetes. Beginning in 1999-2000, the Center for the Health Assessment of Mothers and Children of Salinas prospectively followed women from Monterey County, California (52 obese and 214 nonobese women) and their children. Plasma glucose values obtained 1 hour after a 50-g oral glucose load comprised the exposure. Offspring BMIs were compared with national data to calculate z scores. Increasing pregnancy glucose levels were associated with increased offspring BMI z scores at 7 years of age; a 1-mmol/L increase in glucose corresponded to an increase of 0.11 (standard deviation = 0.044) z-score units (P < 0.05). In nonobese women only, the mean z score over this age range increased with increasing glucose levels. The average BMI z score at 4.5 years of age increased by 0.12 (standard error, 0.059) units for each 1-mmol/L increase in glucose (P = 0.04). In obese women only, increasing glucose was associated with increases in BMI z score over time (P = 0.07). Whether interventions to reduce glucose values in women free of disease could mitigate childhood obesity remains unknown.

Pregnancy glucose levels in women without diabetes or gestational diabetes and childhood cardiometabolic risk at 7 years of age.

OBJECTIVE: To estimate the association between pregnancy glucose values in women without recognized pregestational diabetes or gestational diabetes and cardiometabolic risk in their children. STUDY DESIGN: This longitudinal cohort study of 211 Mexican American mother-child pairs participating in the Center for the Health Assessment of Mothers and Children of Salinas study used multiple logistic regression to estimate the children's risk of nonfasting total cholesterol, nonfasting triglycerides, blood pressure (BP), and waist circumference (WC) ≥75th percentile at 7 years of age associated with a 1-mmol/L (18-mg/dL) increase in maternal pregnancy glucose level, measured 1 hour after a 50-g oral glucose load. RESULTS: The ORs for children in the upper quartile of diastolic BP, systolic BP, and WC associated with a 1-mmol/L increase in pregnancy glucose level were 1.39 (95% CI, 1.10-1.75), 1.38 (95% CI, 1.10-1.73), and 1.25 (95% CI, 1.02-1.54), respectively. Prepregnancy obesity was independently associated with increased odds of children belonging to the upper quartile of WC; maternal sugar-sweetened beverage consumption and gestational weight gain prior to the glucose test were not independently associated with any of the cardiometabolic outcomes. CONCLUSION: In Mexican American women without recognized pregestational diabetes or gestational diabetes, we found an association between increasing pregnancy glucose values and the children's diastolic and systolic BPs and WC at 7 years of age. Whether interventions to reduce pregnancy glucose values, even if below levels diagnostic of overt disease, will mitigate high BP and abdominal obesity in late childhood remains to be determined.