OBJECTIVE

To quantify the association between a combination of modifiable prepregnancy lifestyle factors and the risk of adverse pregnancy outcomes (APOs).

DESIGN

Prospective cohort study.

SETTING

The Japan Environment and Children's Study.

POPULATION

A total of 79 703 pregnant Japanese women without chronic disease.

METHODS

Maternal lifestyle before pregnancy was assessed using a self-administered questionnaire. A healthy lifestyle score (HLS, 0-5 points) was calculated based on adherence to five prepregnancy healthy lifestyle factors: healthy weight, high-quality diet, regular physical activity, not smoking, and not drinking alcohol. Relative risks (RRs) and 95% credible intervals (CrIs) were estimated using a Bayesian log-binomial regression model.

MAIN OUTCOME MEASURES

Composite APOs, defined as the development of any APO, including gestational diabetes, hypertensive disorders of pregnancy, preterm birth, low birth weight, and small-for-gestational-age, transcribed from medical records.

RESULTS

A total of 13 894 women (17.4%) experienced one or more APOs. HLS was inversely associated with the risk of APOs in a dose-response manner. Women with an HLS of 5 points had a 33% (RR 0.67; 95% CrI, 0.61-0.74) lower risk of APOs than those with the lowest HLS (0-1 points). The population attributable fraction of five healthy lifestyle factors was 10.3%. A 1-point increase of HLS could have reduced APO cases by 6.6%.

CONCLUSIONS

A higher HLS was associated with a lower risk of APOs, suggesting that adopting a healthy lifestyle before pregnancy may reduce the risk of APOs, which can increase the risk of future chronic diseases in both mother and child.