Comparison of methods for identifying small-for-gestational-age infants at risk of perinatal mortality among obese mothers: a hospital-based cohort study.

Objective: To assess differences in small-for-gestational age (SGA) classifications for the detection of neonates with increased perinatal mortality risk among obese women and subsequently assess the association between prepregnancy body mass index (BMI) status and SGA.
Design: Hospital-based cohort.
Setting: Twelve US clinical centres (2002-08).
Population: A total of 114 626 singleton, nonanomalous pregnancies.
Methods: Data were collected using electronic medical record abstraction. Relative risks (RR) with 95% CI were estimated.
Main Outcome Measures: SGA trends (birthweight < 10th centile) classified using population-based (SGA _POP ), intrauterine (SGA _IU ) and customised (SGA _CUST ) references were assessed. The SGA-associated perinatal mortality risk was estimated among obese women. Using the SGA method most associated with perinatal mortality, the association between prepregnancy BMI and SGA was estimated.
Results: The overall perinatal mortality prevalence was 0.55% and this increased significantly with increasing BMI (P < 0.01). Among obese women, SGA _IU detected the highest proportion of perinatal mortality cases (2.49%). Perinatal mortality was 5.32 times (95% CI 3.72-7.60) more likely among SGA _IU neonates than non-SGA _IU neonates. This is in comparison with the 3.71-fold (2.49-5.53) and 4.81-fold (3.41-6.80) increased risk observed when SGA _POP and SGA _CUST were used, respectively. Compared with women of normal weight, overweight women (RR = 0.82, 95% CI 0.78-0.86) and obese women (RR = 0.80; 95% CI 0.75-0.83) had a lower risk for delivering an SGA _IU neonate.
Conclusion: Among obese women, the intrauterine reference best identified neonates at risk of perinatal mortality. Based on SGA _IU , SGA is less common among obese women but these SGA babies are at a high risk of death and remain an important group for surveillance.
Tweetable Abstract: SGA is less common among obese women but these SGA babies are at a high risk of death.
(Published 2016. This article is a U.S. Government work and is in the public domain in the USA.)