Outcome Measures
The
primary outcome was the incidence of PE and the secondary outcomes
included the gestation of birth (allowing assessment of preterm birth)
and birth weight (allowing assessment of the fetus is small for
gestational age). The clinical safety of aspirin was evaluated by the
occurrence of antenatal or postpartum hemorrhage. PE was defined by
evaluated blood pressure (blood pressure≥140/90mmHg associated with
proteinuria (>300 mg/day) or blood pressure≥160/110mmHg
alone) after 20 weeks of gestational
age.13,
15 Blood pressure was measured by a
mercury sphygmomanometer and urine samples were collected and tested by
the clinical laboratory in each hospital. Once diagnosed, patients would
be treated as standard treatment guidelines. The fetus being small for
gestational age (SGA) was defined as the birth weight of either twin was
below the 10th percentile of the average in the same
gestational age. PTB was regarded as delivering before 34 weeks 0 days
for twin pregnancies.16,
17 When calculating the amount of
bleeding, intraoperative blood loss was recorded by the container of
suction apparatus, while postoperative bleeding volume was counted by
the weighing method. Cesarean postpartum hemorrhage was defined as
postoperative bleeding volume more than 1000ml in 24h. These diagnostic
criteria were unified in two centers before the cohort study was
initiated.