Minimization of bias in measures of gestational weight gain

Abstract

Summary Gestational weight gain (GWG) is an important predictor of adverse pregnancy outcomes including gestational diabetes, preterm birth, delivery by caesarean and post‐partum weight retention. The Institute of Medicine guidelines on GWG are widely adopted, and GWG is widely researched as an outcome of interest in lifestyle interventions during pregnancy. However, estimation of prepregnancy weight and measurement of weight prior to delivery introduce bias into measures of GWG. This review discusses the sources of bias in measures of GWG and the potential effect of bias on the relationship between adverse pregnancy outcomes associated with GWG. Bias in measures of GWG can be minimized by using measured weight at the first antenatal appointment in early pregnancy rather than self‐reported prepregnancy weight and by adjusting for gestational age when the last weight is collected earlier than the delivery date. Bias owing to gestational age is an important potential confounder in the relationship between GWG and adverse pregnancy outcomes.

The association between pre-gravid and first trimester maternal weight and its implications for clinical research studies

“…However, each of these options has inherent limitations. Previous studies have documented that self-report of weight can be prone to under-estimation in young women 10,11 A recent model for predicting pre-gravid weight from clinical parameters measured in pregnancy showed strong correlation with self-report but varied markedly in its performance between two study populations in which it was tested 12 . In this context, the simple approach of treating weight measurement in first trimester as a surrogate for pre-gravid weight has been widely adopted in research studies.…”

Identifying optimal ranges of weight gain at the end of the second trimester result from a population-based cohort study

“…However, when applying Asian regional BMI categories, rates of GWG above guidelines and related clinical outcomes were similar across continents. With the development of prenatal care, weight assessment and intervention were becoming more accurate ( 8 ) . Some studies have established specific GWG recommendation ranges for local populations ( 9 ) , while others have focused on the effects of GWG in different trimesters on pregnancy outcomes ( 10 ) .…”

Editorial: The importance of gestational weight gain

“…Worldwide, rising adiposity in pregnancy has increasingly adverse health implications for the health of women and the next generation. Both pre‐pregnancy body mass index (BMI) and gestational weight gain (GWG) are independent predictors of adverse pregnancy outcomes as highlighted in this issue by Stamm et al 1 This underpins the 2009 US Institute of Medicine (IOM) updated guidelines 2 recommending healthy GWG targets across BMI categories. Specifically, IOM guidelines suggest GWG of 12.5–18 kg for those with pre‐pregnancy BMI <18.5 kg/m 2 (women who are considered underweight); 11 .5–16 kg for 18.5–24.9 kg/m 2 (women who are considered normal weight); 7–11.5 kg for BMI 25–29.9 kg/m 2 (women who are considered overweight) and 5–9 kg for BMI ≥30 kg/m 2 (women who are considered to have obesity).…”

“…Specifically, IOM guidelines suggest GWG of 12.5–18 kg for those with pre‐pregnancy BMI <18.5 kg/m 2 (women who are considered underweight); 11 .5–16 kg for 18.5–24.9 kg/m 2 (women who are considered normal weight); 7–11.5 kg for BMI 25–29.9 kg/m 2 (women who are considered overweight) and 5–9 kg for BMI ≥30 kg/m 2 (women who are considered to have obesity). Setting and reaching GWG targets therefore require accurate measurement of both BMI and GWG, yet major limitations exist in current approaches to these measurements as outlined in this issue by Stamm et al 1 …”

“…The authors highlight that current antenatal guidelines vary considerably and while most endorse measurement of weight, height and BMI at commencement of antenatal care, routine GWG monitoring recommendations, including frequency of monitoring, vary considerably 3,4 . Stamm et al also discuss how bias can affect observed and reported relationships between GWG and adverse pregnancy outcomes and how that bias may be limited 1 . Measured pre‐pregnancy weight is ideal to define healthy GWG, yet proxies include self‐reported pre‐pregnancy weight (within 12 months of pregnancy) or weight measured in the first trimester are often used.…”