Estimating bias in derived body mass index in the Maternity Experiences Survey

Gestational weight loss and fetal growth in uncomplicated pregnancies among women with obesity: a population-based retrospective cohort study

OBJECTIVE

The impact of gestational weight loss (GWL) on fetal growth among women with obesity remains unclear. This study aimed to examine the association between weight loss during pregnancy among women with body mass index (BMI) ≥ 30 kg/m2 and the risk of small-for-gestational-age (SGA) and large-for-gestational-age (LGA) neonates.

METHODS

We conducted a retrospective, population-based cohort study of women with pre-pregnancy obesity that resulted in a singleton live birth in 2012-2017, using birth registry data in Ontario, Canada. Women with pregnancy complications or health conditions which could cause weight loss were excluded. GWL is defined as negative gestational weight change (≤0 kg). The association between GWL and fetal growth was estimated using generalized estimating equation models and restricted cubic spline regression analysis. Stratified analysis was conducted by obesity class (I:30-34.9 kg/m2, II:35-39.9 kg/m2, and III + : ≥40 kg/m2).

RESULTS

Of the 52,153 eligible women who entered pregnancy with a BMI ≥ 30 kg/m2, 5.3% had GWL. Compared to adequate gestational weight gain, GWL was associated with an increased risk of SGA neonates (aRR:1.45, 95% CI: 1.30-1.60) and a decreased risk of LGA neonates (aRR: 0.81, 95% CI:0.73-0.93). Non-linear L-shaped associations were observed between gestational weight change and SGA neonates, with an increased risk of SGA observed with increased GWL. On the contrary, non-linear S-shaped associations were observed between gestational weight change and LGA neonates, with a decreased risk of LGA observed with increased GWL. Similar findings were observed from the stratified analysis by obesity class.

CONCLUSION

These findings highlight that GWL in women with obesity may increase the risk of SGA neonates but reduce the risk of LGA neonates. Recommendations of GWL for women with obesity should be interpreted with caution.

Prevalence of and risk factors for excess weight gain in pregnancy: a cross-sectional study using survey data

BACKGROUND

Maternal weight gain during pregnancy is required for fetal development; however, excess gestational weight gain is associated with increased maternal and neonatal morbidity. We aimed to determine the proportion of Canadian women who gained excess weight during pregnancy and to identify risk factors for excess gestational weight gain.

METHODS

Self-reported data on maternal weight gain were collected from the 2015/16 and 2017/18 cycles of the Canadian Community Health Survey (CCHS), a cross-sectional population-based survey. We included females aged 15 to 54 years with data on height, prepregnancy weight and gestational weight gain. We defined excess gestational weight gain in terms of preconception body mass index (BMI) according to the 2009 guideline of the US Institute of Medicine. We used logistic regression to evaluate potential risk factors for excess gestational weight gain.

RESULTS

Of 1 335 615 Canadian women (weighted from approximately 9300 survey respondents), 422 043 (32%) gained excess weight during pregnancy. Women with obesity had 33% lower odds of gaining excess weight relative to women with overweight (odds ratio 0.67, 95% confidence interval 0.48-0.94). Risk factors for excess gestational weight gain were lower education level, white or Indigenous identity, smoking, mood disorder, anxiety disorder and Canadian citizenship.

INTERPRETATION

One-third of Canadian women in this survey had excess gestational weight gain during pregnancy, and women with obesity had lower odds of gaining excess weight during pregnancy relative to women with overweight. Strategies are needed to reduce the proportion of Canadian women who gain excess weight during pregnancy, regardless of preconception BMI.

Gestational Weight Gain and Long-term Maternal Obesity Risk: A Multiple-Bias Analysis

BACKGROUND

Lifecourse research provides an important framework for chronic disease epidemiology. However, data collection to observe health characteristics over long periods is vulnerable to systematic error and statistical bias. We present a multiple-bias analysis using real-world data to estimate associations between excessive gestational weight gain and mid-life obesity, accounting for confounding, selection, and misclassification biases.

METHODS

Participants were from the multiethnic Study of Women's Health Across the Nation. Obesity was defined by waist circumference measured in 1996-1997 when women were age 42-53. Gestational weight gain was measured retrospectively by self-recall and was missing for over 40% of participants. We estimated relative risk (RR) and 95% confidence intervals (CI) of obesity at mid-life for presence versus absence of excessive gestational weight gain in any pregnancy. We imputed missing data via multiple imputation and used weighted regression to account for misclassification.

RESULTS

Among the 2,339 women in this analysis, 937 (40%) experienced obesity in mid-life. In complete case analysis, women with excessive gestational weight gain had an estimated 39% greater risk of obesity (RR = 1.4, CI = 1.1, 1.7), covariate-adjusted. Imputing data, then weighting estimates at the guidepost values of sensitivity = 80% and specificity = 75%, increased the RR (95% CI) for obesity to 2.3 (2.0, 2.6). Only models assuming a 20-point difference in specificity between those with and without obesity decreased the RR.

CONCLUSIONS

The inference of a positive association between excessive gestational weight gain and mid-life obesity is robust to methods accounting for selection and misclassification bias.

Characteristics associated with uncomplicated pregnancies in women with obesity: a population-based cohort study

BACKGROUND

Approximately one in five pregnant women have obesity. Obesity is associated with an increased risk of antenatal, intrapartum, and perinatal complications, but many women with obesity have uncomplicated pregnancies. At a time where maternity services are advocating for women to make informed choices, knowledge of the chance of having an uncomplicated (healthy) pregnancy is essential. The objective of this study was to calculate the rate of uncomplicated pregnancy in women with obesity and evaluate factors associated with this outcome.

METHODS

This prospective cohort study was conducted using the Ontario birth registry dataset in Canada (703,115 women, April 2012-March 2017). The rate of uncomplicated or complicated composite pregnancy outcomes (hypertensive disorders of pregnancy, gestational diabetes, preterm birth, neonate small- or large- for gestational age at birth, congenital anomaly, fetal death, antepartum bleeding or preterm prelabour membrane rupture) were calculated for women with and without obesity. Associations between uncomplicated pregnancy and maternal characteristics were explored in a population of women with obesity but without other pre-existing co-morbidities (e.g., essential hypertension) or obstetric risks identified in the first trimester (e.g., multiple pregnancy), using log binomial regression analysis.

RESULTS

Of the studied Ontario maternity population (body mass index not missing) 17·7% (n = 117,236) were obese. Of these 20·6% had pre-existing co-morbidities or early obstetric complicating factors. Amongst women with obesity but without early complicating factors, 58·2% (n = 54,191) experienced pregnancy without complication; this is in comparison to 72·7% of women of healthy weight and no early complicating factors. Women with obesity and no early pregnancy complicating factors are more likely to have an uncomplicated pregnancy if they are multiparous, younger, more affluent, of White or Black ethnicity, of lower weight, with normal placental-associated plasma protein-A and/or spontaneously conceived pregnancies.

CONCLUSIONS

The study demonstrates that over half of women with obesity but no other pre-existing medical or early obstetric complicating factors, proceed through pregnancy without adverse obstetric complication. Care in lower-risk settings can be considered as their outcomes appear similar to those reported for low-risk nulliparous women. Further research and predictive tools are needed to inform stratification of women with obesity.

Minimization of bias in measures of gestational weight gain

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.

Effect of pre-pregnancy body mass index on respiratory-related neonatal outcomes in women undergoing elective cesarean prior to 39 weeks

Objective To examine the association between pre-pregnancy body mass index (BMI) and neonatal respiratory-related outcomes among women who underwent an elective cesarean section (CS). Methods A retrospective cohort study was conducted using the Centers for Disease Control and Prevention (CDC)'s 2009-2013 period linked birth/infant death dataset. Women who had elective CSs at term were categorized by their pre-pregnancy BMI as normal, overweight, obese or morbidly obese. Odds ratios (OR) and 95% confidence intervals (CIs), adjusted for baseline characteristics, were calculated using multivariate logistic regression to estimate the neonatal risks in relation to maternal pre-pregnancy BMI. Results Our cohort consisted of 717,080 women, of whom 39.9% had normal BMI, 27.0% were overweight, 25.7% obese and 7.4% morbidly obese. A dose-dependent relationship between maternal pre-pregnancy BMI and assisted ventilation was seen. Furthermore, infants born to morbidly obese women were at significantly increased risk for assisted ventilation over 6 h (OR 1.24, 95% CI 1.15-1.35) and admission to intensive care units (OR 1.17, 95% CI 1.13-1.21). Infant mortality rates were 4.2/1000 births for normal weight women, and 5.5/1000 births among the morbidly obese group (OR 1.43, 95% CI 1.25-1.64). Risk for adverse outcomes was increased with elective SC performed at earlier gestational age, and this effect was not modified by use of corticosteroids. Conclusion Overweight and obese women are at particularly greater risk of adverse newborn outcomes when elective CSs are done before 39 weeks. In these women, elective CSs should be delayed until 39 weeks, as corticosteroid use did not eliminate this association.

Interprovincial variation in pre-pregnancy body mass index and gestational weight gain and their impact on neonatal birth weight with respect to small and large for gestational age

OBJECTIVES

To explore provincial variation in both excess and inadequate pre-pregnancy body mass index (BMI) and gestational weight gain (GWG) and their impact on small- and large-for-gestational-age (SGA, LGA) infants.

METHODS

Four provinces with a perinatal database capturing the required exposures participated: British Columbia (BC), Ontario (ON), Nova Scotia (NS), and Newfoundland and Labrador (NL). In multiple, concurrent retrospective studies, we included women ≥ 19 years, who gave birth from 22⁺⁰ to 42⁺⁶ weeks' gestation, to a live singleton from April 2013-March 2014. From adjusted odds ratios, we calculated population attributable fractions (PAF) of SGA and LGA for BMI and GWG.

RESULTS

The proportion of overweight and obese women increased from western to eastern Canada. In BC, ON, NS, and NL, the proportions of women who were overweight were 21.1%, 24.0%, 23.7%, and 25.4%, while obesity proportions were 14.2%, 18.1%, 24.2%, and 29.8%, respectively. Excess GWG affected 53.9%, 49.9%, 57.6%, and 65.6% of women, respectively. Excess GWG contributed to 29.5-42.5% of LGA, compared with the PAFs for overweight (6.8-12.0%) and obesity (13.2-20.6%). Inadequate GWG's contribution to SGA (4.8-12.3%) was higher than underweight BMI's (2.9-6.2%).

CONCLUSION

In this interprovincial study, high and increasing proportions of women from west to east had excess pre-pregnancy BMI, and between half to two thirds had excess GWG. The contributions of GWG outside of recommendations to SGA and LGA were greater than that of low or high BMI. GWG is a potentially modifiable determinant of SGA and LGA across Canada.