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Abstract Background The rate of low birth weight or preterm birth is known to vary according to the birth place of mothers. However, in Japan, studies that investigated the association between maternal nationalities and adverse birth outcomes are few. In this study, we investigated the association between maternal nationalities and adverse birth outcomes. Methods We obtained live birth data from the Vital Statistics 2016–2020 of the Ministry of Health, Labour, and Welfare. We used data on maternal age, sex, parity, gestational age, birth weight, number of fetuses, household occupation, paternal nationality, and maternal nationality for each infant. We compared the rates of preterm birth and low birth weight at term among mothers whose nationalities were Japan, Korea, China, Philippines, Brazil, and other countries. Log binomial regression model was used to investigate the association between maternal nationality and the two birth outcomes using the other infants’ characteristics as covariates. Results In the analysis, data on 4,290,917 singleton births were used. Mothers from Japan, Korea, China, the Philippines, Brazil, and other nations had preterm birth rates of 4.61%, 4.16%, 3.97%, 7.43%, 7.69%, and 5.61%, respectively. The low birth weight rate among Japanese mothers was 5.36% and was the highest among the maternal nationalities. Regression analysis showed that the relative risk for preterm birth among Filipino, Brazilian, and mothers from other countries (1.520, 1.329, and 1.222, respectively) was statistically significantly higher compared with Japanese mothers. In contrast, the relative risk for Korean and Chinese mothers (0.870 and 0.899, respectively) was statistically significantly lower compared with Japanese mothers. Mothers from Korea, China, the Philippines, Brazil, and other nations had a relative risk for low birth weight that was statistically significantly lower than that of Japanese mothers (0.664, 0.447, 0.867, 0.692, and 0.887, respectively). Conclusions Support for mothers from the Philippines, Brazil, and other countries are necessary to prevent preterm birth. A future study is necessary to investigate the differences in characteristics among mothers of different nationalities in order to uncover the reason for the high risk for low birth weight among Japanese mothers.

Abstract Background Women with nausea and vomiting of pregnancy (NVP) have higher birth weight infants, while those with hyperemesis gravidarum, a severe manifestation of NVP, have lower birth weight infants. We aimed to investigate the associations between maternal weight loss (a consequence of hyperemesis gravidarum), NVP, and infant birth weight. Methods This study was a secondary analysis of a nationwide birth cohort in Japan. Singleton pregnancies delivered at 28–41 weeks of gestation were included in the analysis. Women were categorized based on their weight change in the 1st trimester (as a proportion to their pre-pregnancy weight: > + 3%, > 0 to + 3%, > -3 to 0%, > -5 to -3%, ≤ -5%) and severity of NVP (no nausea, only nausea, vomiting but able to eat, vomiting and unable to eat). The effects of weight change and severity of NVP on infant birth weight and small for gestational age (SGA) were assessed using regression models. We further examined how these effects could be modified by maternal weight gain up to the 2nd trimester. Results Among 91,313 women, 5,196 (5.7%) lost ≥ 5% of their pre-pregnancy weight and 9,983 (10.9%) experienced vomiting and were unable to eat in the 1st trimester. Women with weight loss ≥ 5% in the 1st trimester had infants 66 (95% CI: 53, 78) g lighter and higher odds of SGA (aOR: 1.29; 95% CI: 1.14, 1.47) than women who gained > 3% during the same period. However, when adjusting for weight gain up to the 2nd trimester, women with weight loss ≥ 5% in the 1st trimester had infants 150 (95% CI: 135, 165) g heavier and lower odds of SGA (aOR: 0.39; 95% CI: 0.33, 0.46) than those who gained > 3% during the same period. In contrast, women with more severe NVP tended to have infants with larger birth weight and lower odds of SGA compared to women without NVP. These trends were strengthened when adjusting for weight gain up to the 2nd trimester. Conclusions Our study suggests the possibility that reduced fetal growth in pregnancies with hyperemesis gravidarum may be caused by the lack of catch-up in gestational weight gain up to the 2nd trimester.

Abstract Background The adequate maternal sleep duration required for favorable obstetric outcomes is unknown. We evaluated the association between maternal sleep duration and low birth weight infants, small for gestational age infants, and macrosomia. Methods Participants enrolled in the Japan Environment and Children’s Study, a nationwide birth cohort study, with singleton pregnancies after 22 weeks, who gave birth between 2011 and 2014 were enrolled and categorized into five groups according to maternal sleep duration during pregnancy: 4000 g), with women with maternal sleep duration of 6.0–7.9 h as the reference, using a multiple logistic regression model. Results In total, 82,171 participants were analyzed. The adjusted odds ratios (95% confidence intervals) for low birth weight infants in women with maternal sleep duration of 9.0–9.9 h and 10.0–12.0 h and for small for gestational age infants in women with maternal sleep duration of 9.0–9.9 h were 0.90 (0.83–0.99), 0.86 (0.76–0.99), and 0.91 (0.82–0.99), respectively, before adjusting for excessive gestational weight gain. No significant association was observed between maternal sleep duration and these outcomes after adjusting for excessive gestational weight gain. Among women with appropriate gestational weight gain, the adjusted odds ratios (95% confidence intervals) for low birth weight infants and for small for gestational age infants with sleep duration of 9.0–9.9 h were 0.88 (0.80–0.97) and 0.87 (0.78–0.97), respectively. Conclusions Maternal sleep duration of 9.0–9.9 h was significantly associated with the decreased incidence of low birth weight infants and small for gestational age infants in pregnant women with appropriate gestational weight gain, compared with that of 6.0–7.9 h. Care providers should provide proper counseling regarding the association between maternal sleep duration and neonatal birth weight and suggest comprehensive maternal lifestyle modifications to prevent low birth weight and small for gestational age infants.

Abstract Background Gestational diabetes mellitus (GDM) has serious effects on both mother and child. Like Type 2 Diabetes Mellitus, it is increasing in prevalence world-wide. In addition to obesity, sleep duration has been named an important risk factor. Using a large cohort study, including data from 48,787 participants of the Japan Environment and Children’s Study (JECS), we examined the association between sleep duration and both random blood glucose levels and GDM rates during pregnancy. Methods Random blood glucose levels were measured during pregnancy. GDM diagnosis was based on the results of 75 g oral glucose tolerance test. Additional anthropometric data was collected from questionnaires for statistical analysis. Results Compared to mothers averaging 7 to

Abstract Background In Japan, although the number of females who continue to work after marriage has recently increased, the proportion of those working while parenting their infants is still not clearly increasing, indicating that it is still difficult for them to continue working after delivery. The present study aimed to clarify factors influencing females’ continuation of work, using data obtained by continuously following up the same subjects and focusing on occupation changes, family environments, and the type of employment after pregnancy or delivery. Methods Based on the results of the questionnaire survey, which was conducted involving 164 participants at 4 universities, as part of the Japan Environment and Children’s Pilot Study (JECS Pilot Study) led by the Ministry of Environment and the National Institute for Environmental Studies, the occupational status was compared between the detection of pregnancy (weeks 0 to 7) and 1 year after delivery. Results compared with changed their occupations significantly more frequently (OR = 5.07, 95% CI = 2.57–10.01, P in detail, occupation changes were particularly marked among (OR = 12.48, 95% CI = 4.43–35.15, P > (OR = 10.36, 95% CI = 1.59–67.38, P = 0.014) and > (OR = 15.15, 95% CI = 2.55–90.17, P = 0.003). Conclusions Analysis revealed that the type of employment, rather than the category of occupation, was associated with the continuation of work after pregnancy or delivery more closely, as compared with continued to work less frequently. Furthermore, on comparison of the category of occupation among , < > and > were shown to be more likely to continue to be engaged in the same occupation after pregnancy or delivery. These differences may be related to availability of the child-care leave program and other support resources, therefore, it may be important to establish social systems that enable all females, to use these support resources if they wish, and actively work, while delivering and parenting their children.

Abstract Objectives Small for gestational age infants have an increased risk of immediate complications, short-term morbidity and mortality, and long-term neurologic and metabolic disorders in adulthood. Previous research has shown that reduced sleep duration is a risk factor for SGA birth. However, only a few studies have evaluated maternal sleep as a risk factor for SGA birth. In the present study, we investigated the relationship between the amount and quality of mothers’ sleep and infants’ birth weight. Results This cohort study (n = 8631) used data from the Japan Environment and Children’s Study, an ongoing cohort study that began in January 2011. Data on sleep status (sleep duration and one indicator of sleep quality) and potential confounding factors were recorded. A log-binomial regression model was used to estimate the risk of small for gestational age birth, and the results were expressed as risk ratios and their respective 95% confidence interval. No significant results were observed for sleep duration or tiredness upon waking. Neither the amount nor the quality of mothers’ sleep was associated with the risk of small for gestational age birth.