Methods
This retrospective cohort study was conducted at West China Second
University Hospital (Sichuan University), a tertiary care hospital.
Women with a history of CS who gave birth from January 2016 to December
2016 at West China Second University Hospital were included in this
cohort. Data were obtained from the electronic medical system and were
supplemented by information from medical records. Two trained
abstractors were instructed to review and abstract data from the medical
chart. The ethics committee and data inspectorate of West China Second
University Hospital of Sichuan University approved this study (ref.
number 2016-010; date of approval 2016-05-25). We conducted this
observative study following the STROBE guideline.
Our primary analyses included all women who had at least one previous CS
at 28 to <42 weeks of gestation and delivered at 28 to
<42 weeks of gestation. We excluded women who met the
following criteria: (1) underwent uterine surgery other than CS; (2) did
not receive routine antenatal care; (3) had multiple pregnancies; and
(4) had fetal malformations.
IPI was defined as the number of months between the date of last
cesarean operation and the conception date of the subsequent delivery,
which was estimated by the delivery date of the index pregnancy minus
its gestational age at birth. The IPI was categorized into four groups:
less than 24 months, 24 to 59 months, 60 to 119 months, and 120 months
or greater.
Maternal outcomes included anemia in late pregnancy, GHP, GDM, an
abnormal placental position, pernicious placenta, placenta accreta,
placental abruption, premature rupture of membranes (PROM), uterine
rupture (including incomplete and complete uterine rupture), postpartum
hemorrhage (PPH), and hysterectomy. According to the WHO guidelines,
anemia in late pregnancy was defined as a hemoglobin concentration less
than 110 g/L between 32 and 42 weeks of gestation.17The definitions of gestational hypertension complied with the consensus
statement from the International Society of Study of Hypertension in
Pregnancy (ISSHP).18 The definitions of GDM (where
Grade A1 indicates that blood glucose is well controlled by nondrug
therapy during pregnancy and Grade A2 indicates that blood glucose
should be controlled by drugs during pregnancy) complied with the WHO
criteria.19 Uterine rupture was measured during CS by
experienced obstetricians, and complete rupture was defined as a tear
through all layers of the uterine wall, and incomplete rupture was
defined as a tear in the muscular layers with intact serosa or amniotic
membranes.20 Adverse fetal outcomes included preterm
birth, admission to the NICU, low 1-min Apgar score, and LBW. LBW was
defined as a birth weight less than 2500 g, and a low 1-min Apgar score
was defined as an Apgar score of less than 10 during 1 minute after
birth evaluated by a professional obstetrician.
The demographic and clinical characteristics of the four groups may be
significantly different, and these factors may be potential confounding
factors affecting the association between IPI and perinatal outcomes. We
established multivariable logistic regression analysis models to adjust
for these factors and then analyzed the effect of the IPI after CS on
adverse maternal and fetal outcomes. Since previous studies have
confirmed that emergency CS significantly increases the risk of adverse
perinatal outcomes,21 we established analysis models
to separately analyze the relationships between IPI after emergency CS
or elective CS and pregnancy outcomes by using a multivariable logistic
regression method.
Sociodemographic characteristics and adverse pregnancy outcomes were
compared among the four groups, the chi-squared test was used for
categorical variables, and one-way analysis of variance was used for
continuous variables. Multivariable logistic regression analysis was
separately conducted for the association between different IPIs and each
pregnancy outcome after controlling for the known and suspected
confounding factors, and the analysis used an IPI of 24-59 months as the
reference category, as it was the recommended IPI by WHO
guidelines.1 Data analyses were performed using the
software package SPSS statistics version 21.0 (SPSS Inc.) A p-value
< 0.05 for both sides was considered significant.