Study population
We conducted a prospective cohort study in the
Department of Obstetrics of The
Eighth Affiliated Hospital, Sun Yat-sen University and Guangdong Women
and Children Hospital between January 2019 and December 2020. The study
design was approved by the local Ethical and Research Committees of the
two hospitals. Pregnant women were recruited
before 24 weeks of gestation. For
most women, the expected delivery date was based on the last menstrual
period date, while for a small proportion, this estimate was updated
following an ultrasound scan. Those pregnant women would not be enrolled
if they had any of the following exclusion criteria: multiple pregnancy,
ischemic heart disease, stroke, peripheral vascular disease, diagnosis
of diabetes, or/and hypertension before the current
pregnancy.
In
addition, individuals who had a normal diet were selected;
vegetarians and malnourished were excluded. Every participant gave full
and informed consent to participate in the study. Initially, 1924 women
were enrolled in the study. Figure 1 showed the filtering and processing
flow chart of the study population. 9 women dropped out midway, 139
women were subsequently excluded because they were discovered to have
exclusion criteria or had no blood sample to measure serum 25(OH) D
concentrations, 2 women were excluded for implausible information, 8
women did not consent to the use of outcome data. Finally, there are 1766
women with available data for analysis. Personal medical histories were
self-identified by the participants.