To evaluate the association between urinary 8-hydroxy-2'-deoxyguanosine (U8-OHdG) level—a marker of oxidative stress—and the incidence of preterm births (PTBs).

Prospective cohort study.

The Japan Environment and Children’s Study (JECS).

Data from 92 715 women with singleton pregnancies at and after 22 weeks of gestation who were enrolled in the JECS, a nationwide birth cohort study, between 2011 and 2014 were analysed. U8-OHdG levels were assessed once in the second/third trimester using liquid chromatography–tandem mass spectrometry. Participants were categorised into the following three or five groups: low (

Adjusted OR (aOR) for PTB before 37 and 34 weeks of gestation were calculated using a multivariable logistic regression model while adjusting for confounding factors; the moderate or lowest U8-OHdG group was used as the reference, respectively.

The aORs for PTB before 37 weeks of gestation in the high U8-OHdG group were 1.13 (95% CI 1.05 to 1.22) and 1.13 (95% CI 1.04 to 1.23) after stratification. The aOR for PTB before 37 weeks in the fourth group was 0.90 (95% CI 0.81 to 0.99). After stratification, the aORs for PTB before 37 and 34 weeks in the fifth group were 1.15 (95% CI 1.03 to 1.29) and 1.46 (95% CI 1.08 to 1.97), respectively.

High U8-OHdG levels were associated with increased PTB incidence, especially in participants without representative causes for artificial PTB. Our results can help identify the mechanisms leading to PTB, considering the variable aetiologies of this condition; further validation is needed to clarify clinical impacts.

We examined literacy related to healthy gestational weight gain (GWG) in immigrant and native Japanese mothers and determined whether it is associated with children’s birth weight.

Longitudinal cohort study.

As the baseline survey in the Japan Environment and Children’s Study (JECS), mothers completed self-administered questionnaires distributed by hand during pregnancy. The self-administered questionnaires used in this study were distributed by mail 6 months after delivery. Children’s birth weight, actual GWG and any complications during delivery were recorded by obstetricians collaborating with JECS.

Of 97 452 mothers who consented to participate in the JECS during pregnancy between January 2011 and March 2014, 67 953 were included in this study after exclusions for multiple births, multiple instances of consent by the same pregnant woman, miscarriages/stillbirths or withdrawal from the study within 3 years after participating. In total, 324 immigrant mothers and 963 native Japanese mothers were selected by propensity score matching for analysis.

Data were collected on maternal literacy related to healthy GWG at the baseline survey, and data on actual GWG and children’s birth weight were collected by obstetricians. The associations of knowledge about healthy GWG and mothers’ actual GWG with maternal nativity status were examined using a ² or Student’s t-test.

More native Japanese mothers than immigrant mothers knew the appropriate GWG and reason the for needing to know this. Actual GWG was significantly higher among the immigrant mothers, but was within the recommended range. The low birthweight (LBW) incidence was significantly higher among the native mothers.

Immigrant mothers to Japan had less knowledge about appropriate GWG, but their actual GWG was appropriate and they delivered fewer LBW infants than native Japanese mothers. These findings may indicate the presence of other protective factors for pregnancy or delivery among immigrant mothers.