Change in Pre-Pregnancy Body Mass Index in Relation to the COVID-19 Pandemic

During the coronavirus disease 2019 (COVID-19) pandemic, daily physical activity has declined among many individuals.¹ Thus, even at a constant caloric intake, one might expect a rise in body mass index (BMI) during the COVID-19 era. In the short term, this may be of concern for pregnant women. Maternal pre-pregnancy obesity is a known predictor of adverse pregnancy outcomes, such as preeclampsia.² This study evaluated whether maternal pre-pregnancy BMI changed from the era before the COVID-19 pandemic to that during the pandemic.

We used existing, deidentified pregnancy and birth data at St. Michael's Hospital in Toronto, Ontario—a level II inner-city hospital with about 2500 births annually. All singleton livebirths were included from January 1, 2017, to June 30, 2021, with corresponding pre-pregnancy BMI values from March 22, 2016, to November 20, 2020. We excluded women whose pre-pregnancy height and weight were both missing or whose BMI was implausibly reported as <15 kg/m² or >60 kg/m².

Mean maternal pre-pregnancy BMI was aggregated by 1-month time intervals. A segmented regression time series was established, setting the interruption to March 15, 2020 (the onset of the pandemic in Ontario) using a slope function. A washout period, from March 15 to May 15, 2020, was incorporated in the model to account for the period during which the COVID-19 pandemic emerged in Ontario and lockdown protocols were gradually introduced. The mean (95% confidence interval [CI]) change in maternal BMI was calculated from before to during the COVID-19 era. Logistic regression generated an odds ratio for pre-pregnancy obesity (i.e., BMI ≥30 kg/m²) during versus before the pandemic. Potential confounders, such as maternal age and parity, were included in all of the aforementioned analyses.

A total of 9112 women were included pre-pandemic and 591 during the pandemic. The mean (standard deviation) age was 33.0 (4.8) years and median (interquartile ratio) parity was 0 (1) for both groups.

The mean (standard deviation) BMI was 24.9 (6.5) kg/m² pre-pandemic and 25.4 (6.2) kg/m² during the pandemic (Figure). This corresponded to an unadjusted mean difference of 0.5 kg/m² (95% CI 0.0–1.1) and an adjusted mean difference of 0.5 kg/m² (95% CI 0.0–1.0). Segmented regression showed a steeper slope for pre-pregnancy BMI during compared with before the pandemic, with a P-value of 0.06 for the associated effect of the interruption of the COVID-19 pandemic on pre-pregnancy BMI (Figure ).

Figure.

Monthly mean maternal pre-pregnancy body mass index among 9703 women with a singleton livebirth before (blue circles) and during (orange squares) the SARS-CoV-2 pandemic (vertical dashes line).

A washout period from March to May 2020 is included in the segmented regression time series model (1). SARS-CoV-2: severe acute respiratory syndrome coronavirus-2.

Pre-pregnancy obesity occurred in 1255 women (13.8%) pre-pandemic and 103 women (17.4%) during the pandemic, with an unadjusted and adjusted odds ratio of 1.3 (95% CI 1.1–1.7). An incremental rise in maternal pre-pregnancy BMI was observed after the emergence of the COVID-19 pandemic, along with an increased rate of obesity.

This single-centre study was limited to singleton livebirths, with pre-pregnancy BMI collected nearer to the beginning of the pandemic. Physical activity, dietary intake, and cigarette smoking were not accounted for, nor was any unrealized preferential tendency among women with a higher BMI to conceive during the pandemic.

Others recently observed a rise in BMI among children and adolescents related to the COVID-19 pandemic.³ Certainly, if the currently observed finding of a rise in pre-pregnancy BMI is correct and persistent, adverse maternal and perinatal events related to maternal obesity would be expected to emerge. Accordingly, large population-based studies might evaluate trends in pre-pregnancy BMI and pregnancy weight gain related to the COVID-19 pandemic, alongside ensuing adverse outcomes for mother and newborn.