Objective: To evaluate the incidence of adverse pregnancy outcomes (APOs) in women with uterine myomas and clarify the effect of uterine myomas on pregnancy outcomes. Design: Prospective cohort study Setting: The Japan Environment and Children’s Study (between 2011–2014) Population: Women (86,370) with singleton births after 22 weeks of gestation. Methods: Using logistic regression, the adjusted odds ratios (aORs) for APOs were calculated considering women without uterine myomas as the reference. Additionally, we used logistic regression to evaluate the effect of intrauterine infection (II) on the incidence of preterm births (PTB) and preterm premature rupture of membranes (pPROM). Main Outcome Measures: PTB (before 37 and 34 weeks), pPROM, II, and gestational hypertension (GH). Results: In women with uterine myomas, the aORs for PTB before 37 and 34 weeks, pPROM, II, and GH were 1.37 (95% confidence interval [CI], 1.22–1.54), 1.61 (95% CI, 1.27–2.05), 1.65 (95% CI, 1.33–2.04), 1.05 (95% CI, 0.75–1.46), and 1.20 (95% CI, 1.05–1.38), respectively. In women with both uterine myomas and intrauterine infection, the aORs for PTB before 37 weeks and pPROM were not significantly increased. Conclusions: Intra-pregnancy uterine myomas were associated with an increased risk of APOs. II in women with uterine myomas was not associated with PTB or pPROM. These data suggest a potential mechanical disadvantage in pregnant women with uterine myomas. Funding: Ministry of the Environment, Japan Key words: uterine myoma, preterm birth, preterm premature rupture of membrane, intrauterine infection

Objective: To examine the effect of maternal age on placental abruption Design: Prospective cohort study Setting: Fifteen regional centers across Japan Population: We identified 94,410 Japanese women (93,994 without placental abruption and 416 with placental abruption) who were recruited in the Japan Environment and Children’s study between January 2011 and March 2014. Methods: Multiple regression models were used to identify whether maternal age (<20 years, 20–24 years, 25–29 years, 30–34 years, and ≥ 35 years) is a risk factor for placental abruption. The analyses were conducted while considering history of placental abruption, assisted reproductive technology, number of previous deliveries, smoking during pregnancy, body mass index before pregnancy, chronic hypertension, and uterine myoma as confounding factors. Main outcome measures: Maternal age as a risk factor for placental abruption Results: Besides advanced maternal age (≥35 years; adjusted odds ratio [aOR]: 1.7, 95% confidence interval [CI]: 1.1–2.5), teenage pregnancy was also a risk factor for placental abruption (aOR: 2.8, 95% CI: 1.2–6.5) when maternal age of 20–24 years was set as a reference. Conclusions: In the Japanese general population, besides advanced maternal age, teenage pregnancy was also a strong risk factor for placental abruption. The maternal age in Japan is changing since recent decades. Therefore, it is important for obstetric care providers to provide proper counseling to young women based on the up-to-date evidences. Funding: The Japan Environment and Children’s Study was funded by the Ministry of the Environment, Japan