Introduction
According to the recommendations of the World Health Organization (WHO),
the interval from previous live birth and subsequent conception should
be a minimum of 2 years, regardless of the previous delivery
mode.1 In 2016, when the universal one-child policy
was replaced with the two-child policy, all couples in China were
allowed to have a second child.2 Because the one-child
policy had been in place for 36 years in China, this change was very
likely to increase the number of high-risk parturients with typical risk
factors such as advanced maternal age (AMA) and a long interpregnancy
interval (IPI). Additionally, there has also been a sharp increase in
pregnancies with previous cesarean section (CS) due to the high CS rates
over recent decades in China.3,4 Consequently, it is a
great challenge for obstetricians in China to manage the growing number
of high-risk parturients with multiple risk factors, such as AMA, a long
IPI, and previous CS, which have been demonstrated to increase the risk
of adverse pregnancy outcomes, such as uterine
rupture,5,6 gestational hypertension
(GHP),7,8 gestational diabetes mellitus
(GDM),9 preterm delivery, low birth weight (LBW) and
neonatal intensive care unit (NICU) admission.10-15
We performed a preliminary systematic review of the association between
IPI and adverse pregnancy outcomes after previous CS and found that
pregnancy spacing after previous CS
was related to the risk of uterine rupture, the probability of a
successful vaginal birth after CS (VBAC), and the risk of placenta
previa.16 However, we cannot conclude the optimal IPI
after previous CS because different measurements and categorizations of
birth spacing were used in previous studies. Furthermore, 36 years after
implementing the one-child policy, China implemented the two-child
policy broadly; as a result, the number of pregnant women with long IPIs
increased significantly, and this family planning policy caused the
number of pregnancies and deliveries among Chinese women to be quite
different from those of other countries. Thus, there is no relevant
research conducted exclusively for Chinese women. Therefore, we
conducted this large retrospective cohort study to explore the
association between IPI after previous CS and adverse pregnancy
outcomes.