Study design and study population
We performed an observational study using monitoring data collected as
part of the BD surveillance system of Zhejiang Province, China between
2012 and 2018. This system encompassed all births, including live birth,
early fetal loss, stillbirth, and neonatal deaths within 7 days of
birth, that involved a BD and occurred in 90 hospitals located in the 30
regions of Zhejiang Province, which covers one-third of the total number
of births in the province. A total of 54,572 births associated with a BD
were recorded in the system between 2012 and 2018. All the mothers
included in the system underwent routine antenatal health care visits at
least five to ten times during their pregnancies, in line with the
antenatal health care regulations enacted by China’s Ministry of
Health.21 Questionnaire surveys regarding
socio-demographic data (including maternal age, domicile, and
education), obstetric characteristics (including maternal parity,
singleton vs . multiple pregnancy, and prenatal diagnosis), and
birth data (including birth weight, birth outcome, and sex) were
conducted by medical staff in each of the hospitals. Quality control was
performed at the local hospital and provincial levels.
For the purposes of the present study, participants for whom data were
missing regarding whether they had a singleton or multiple pregnancy (n
= 62), period of diagnosis (prenatal or postnatal) (n = 40), the timing
of screening (in which gestational week) (n = 548), the socioeconomic
status of the mother (n = 36), maternal parity (n = 524), or infant sex
(n = 166) were excluded. Thus, ultimately, 53,196 births were included
in the analyses.