Maternal medical background
The maternal medical background information was obtained from the M0 data, which included information on maternal age at the time of delivery, pre-pregnancy body mass index (BMI), the presence of maternal chronic hypertension, and parity; and T1 data, which included information on previous pregnancy complication, maternal smoking status, manner of conception, and pre-pregnancy presence of uterine myoma. The method of conception was categorized as natural or ART-related, with ART defined as conception after in vitro fertilization (IVF) and/or intracytoplasmic sperm injection (ICSI); or cryopreserved, frozen, or blastocyst embryo transfers.11 The mothers were categorized into the following five groups based on the age: <20 years, 20–24 years, 25–29 years, 30–34 years, and ≥35 years. The mothers were also stratified based on the number of previous deliveries, as follows: 0, 1, 2, 3, and ≥4. BMI was calculated according to the criterion of World Health Organization (body weight [kg]/height2 [m2]). We further categorized the participants into three groups according to their BMI: <18.5 kg/m2, 18.5–25.0 kg/m2, and ≥25.0 kg/m2. A self-reported questionnaire during the first trimester provided information on the participants’ smoking habit as follows: “Never,” “Previously did, but quit before realizing current pregnancy,” “Previously did, But quit after realizing current pregnancy,” and “Currently smoking.” The women in “Currently smoking” category were considered as smokers and comprised the smoking category, while the others were considered as non-smokers and comprised the non-smoking category. Maternal participants were also asked to answer the question: “Have you ever been diagnosed as having a uterine myoma in a medical institution?” The participants who answered “yes” were classified as having a uterine myoma. Maternal chronic hypertension was defined as the presence of hypertension before conception. The process of collecting data for pre-pregnancy gynecological complications from the self-reported questionnaire of JECS has been validated previously.12,13