First Birth Cesarean and Risk of Placenta Previa in Second
First Birth Cesarean and Risk of Placenta Previa in Second
Placenta previa can have serious adverse consequences for both mother and baby, including an increased risk of maternal and neonatal mortality, fetal growth restriction and preterm delivery, antenatal and intrapartum hemorrhage, and women may require a blood transfusion or even an emergency hysterectomy. It is a relatively uncommon condition, with an overall incidence in England of 6.3 per 1000 births, but incidence rates are higher among women with advanced maternal age, multiple gestation, high parity, or who smoke or use illegal drugs. The risk of placenta previa is also reported to be higher among women with previous uterine surgery, including cesarean section.
In England, cesarean sections constituted 25% of National Health Service (NHS) deliveries during 2010, and the rates have been rising for both primary and emergency CS. The risk of placenta previa in a pregnancy after a CS delivery has been reported to be between 1.5 and 6 times higher than after a vaginal delivery. A meta-analysis of studies published before 2000 of previous CS as a risk factor for placenta previa found an overall odds ratio of 2.7. However, the overall odds ratio was lower in studies that had better adjustment for confounders. A recent study from the USA that was not included in the meta-analysis, and which used a population-based cohort of 11 million pregnancies, found an adjusted odds ratio of 1.8 for all pregnancies and an adjusted odds ratio of 1.5 for second births only.
Evidence about the risk of placenta previa following a previous CS in UK women is limited to results published 25 years ago. We used the Hospital Episode Statistics (HES), an administrative database of all admissions to NHS hospitals in England, to define a population-based cohort and to quantify the association between CS at first birth and the risk of developing placenta previa in the subsequent pregnancy. We also performed a meta-analysis of the reported results in peer-reviewed articles since 1980.
Background
Placenta previa can have serious adverse consequences for both mother and baby, including an increased risk of maternal and neonatal mortality, fetal growth restriction and preterm delivery, antenatal and intrapartum hemorrhage, and women may require a blood transfusion or even an emergency hysterectomy. It is a relatively uncommon condition, with an overall incidence in England of 6.3 per 1000 births, but incidence rates are higher among women with advanced maternal age, multiple gestation, high parity, or who smoke or use illegal drugs. The risk of placenta previa is also reported to be higher among women with previous uterine surgery, including cesarean section.
In England, cesarean sections constituted 25% of National Health Service (NHS) deliveries during 2010, and the rates have been rising for both primary and emergency CS. The risk of placenta previa in a pregnancy after a CS delivery has been reported to be between 1.5 and 6 times higher than after a vaginal delivery. A meta-analysis of studies published before 2000 of previous CS as a risk factor for placenta previa found an overall odds ratio of 2.7. However, the overall odds ratio was lower in studies that had better adjustment for confounders. A recent study from the USA that was not included in the meta-analysis, and which used a population-based cohort of 11 million pregnancies, found an adjusted odds ratio of 1.8 for all pregnancies and an adjusted odds ratio of 1.5 for second births only.
Evidence about the risk of placenta previa following a previous CS in UK women is limited to results published 25 years ago. We used the Hospital Episode Statistics (HES), an administrative database of all admissions to NHS hospitals in England, to define a population-based cohort and to quantify the association between CS at first birth and the risk of developing placenta previa in the subsequent pregnancy. We also performed a meta-analysis of the reported results in peer-reviewed articles since 1980.
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