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