Study design and Participants
We undertook a retrospective cohort study of women with reproductive age
who participated in the National Free Preconception Health Examination
Project (NFPHEP) from 1st January 2013 to
31st December 2017, successfully became pregnant and
then had pregnancy outcome in Guangdong Province, China. The NFPHEP has
covered all rural counties/districts since 2013, with aim to decline
adverse pregnancy outcomes through providing free health examination
before conception, counselling services for reproductive couples. The
study design, organization and implementation have been described
previously7-10.
In the current analysis, we excluded women who did not measure weight
and height before pregnancy; women with chronic disease (including
anaemia, hypertension, heart disease, hepatitis B, epilepsy, thyroid
disease, chronic nephritis, cancer and diabetes) as they were prone to
receive medical interventions before and during pregnancy. Women with
multiple births or without information on gestational week, birth
weight, delivery method, shoulder dystocia or injury birth or stillbirth
were also excluded.
The NFPHEP was approved by the Institutional Review Board of the Chinese
Association of Maternal and Child Health Studies. Written informed
consent was obtained from the participants before recruitment. The
present study was executed jointly by Guangzhou Medical University and
Guangdong Institute of Family Planning Science and Technology, in which
the review boards determined that this study was exempt for ethical
approval owing to the use of de-identified data.