Premium
Maternal Weight Gain During Pregnancy: Comparing Methods to Address Bias Due to Length of Gestation in Epidemiological Studies
Author(s) -
Hinkle Stefanie N.,
Mitchell Emily M.,
Grantz Katherine L.,
Ye Aijun,
Schisterman Enrique F.
Publication year - 2016
Publication title -
paediatric and perinatal epidemiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.667
H-Index - 88
eISSN - 1365-3016
pISSN - 0269-5022
DOI - 10.1111/ppe.12284
Subject(s) - medicine , logistic regression , singleton , obstetrics , relative risk , gestation , weight gain , population , epidemiology , gestational age , statistics , pregnancy , demography , sample size determination , confidence interval , body weight , mathematics , environmental health , biology , genetics , sociology
Background Studies examining total gestational weight gain (GWG) and outcomes associated with gestational age (GA) are potentially biased. The z ‐score has been proposed to mitigate this bias. We evaluated a regression‐based adjustment for GA to remove the correlation between GWG and GA, and compared it to published weight‐gain‐for‐gestational‐age z ‐scores when applied to a study sample with different underlying population characteristics. Methods Using 65 643 singleton deliveries to normal weight women at 12 US clinical sites, we simulated a null association between GWG and neonatal mortality. Logistic regression was used to estimate approximate relative risks (RR) of neonatal mortality associated with GWG, unadjusted and adjusted for GA, and the z ‐score, overall and within study sites. Average RRs across 5000 replicates were calculated with 95% coverage probability to indicate model bias and precision, where 95% is nominal. Results Under a simulated null association, total GWG resulted in a biased mortality estimate (RR = 0.87; coverage = 0%); estimates adjusted for GA were unbiased (RR = 1.00; coverage = 94%). Quintile‐specific RRs ranged from 0.97–1.03. Similar results were observed for site‐specific analyses. The overall z ‐score RR was 0.97 (84% coverage) with quintile‐specific RRs ranging from 0.64–0.90. Estimates were close to 1.0 at most sites, with coverage from 70–94%. Sites 1 and 6 were biased with RRs of 0.66 and 1.43, respectively, and coverage of 70% and 80%. Conclusions Adjusting for GA achieves unbiased estimates of the association between total GWG and neonatal mortality, providing an accessible alternative to the weight‐gain‐for‐gestational‐age z ‐scores without requiring assumptions concerning underlying population characteristics.