Study design
A retrospective cohort study was conducted at the Shanghai First
Maternity and Infant Hospital, which is one of the largest prenatal care
providers in Shanghai, China, with more than 20,000 births per year. A
total of 114,142 pregnant women
who were issued an antenatal card and received routine antenatal care
from January 2016 to October 2021 were identified as potential
participants. Women with incomplete medical records, a history of
chronic diseases, severe autoimmune diseases, tuberculosis and cancer
before this pregnancy and multiple pregnancies were excluded.
Additionally, women with early pregnancy loss (pregnancy loss before 12
weeks of gestation) were excluded because some pregnant women experience
early pregnancy loss before registering so that it is inaccurate to
estimate the early miscarriage rate through our registering medical
records. The flowchart of participant enrollment is presented inFigure 1 . This study was approved by the Institutional Review
Board of the Shanghai First Maternity and Infant Hospital.