Objective: To estimate the risks of maternal and perinatal morbidity and mortality in a second pregnancy, attributable to caesarean section in a first pregnancy.
Design and setting: Cross-sectional analytic study of hospital births in New South Wales, based on linked population databases.
Participants: 136 101 women with one previous birth who gave birth to a singleton infant in NSW in 1998–2002.
Main outcome measures: Crude and adjusted odds ratios (aOR) and 95% confidence intervals (95% CI) for maternal and perinatal morbidity and mortality.
Results: 19% of mothers had a caesarean section in their first pregnancy. Compared with mothers who had had primary vaginal births, mothers who had had primary caesarean section and undewent labour in the second birth were at increased risk of uterine rupture (aOR, 12.3; 95% CI, 5.0–30.1; P < 0.0001), hysterectomy (3.5; 1.5–8.4; P < 0.01), postpartum haemorrhage (PPH) following vaginal delivery (1.6; 1.4–1.7; P < 0.0001), manual removal of placenta (1.3; 1.1–1.6; P < 0.01), infection (6.2; 4.7–8.2; P < 0.0001) and intensive care unit (ICU) admission (3.1; 2.1–4.7; P < 0.0001); among mothers who did not undergo labour (ie, had an elective caesarean section), there was a lower risk of PPH (0.6; 0.5–0.7; P < 0.0001) and ICU admission (0.4; 0.3–0.5; P < 0.0001). For infants there was increased risk of preterm delivery (1.2; 1.1–1.3; P < 0.0001) and neonatal intensive care unit admission following labour (1.6; 1.4–1.9; P < 0.0001) in the birth after primary caesarean section. The occurrence of stillbirth was not modified by labour.
Conclusions: Caesarean section in a first pregnancy confers additional risks on the second pregnancy, primarily associated with labour. These should be considered at the time caesarean section in the first pregnancy is being considered, particularly for elective caesarean section for non-medical reasons.
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