The risk of abnormal placentation and hemorrhage in subsequent pregnancy following primary elective cesarean delivery.

We aimed to evaluate the relationship between mode of first delivery with subsequent placenta previa, placenta accreta/increta, and significant postpartum hemorrhage (PPH). This retrospective cohort study included women with two consecutive singleton deliveries between 2007 and 2017 at our institution if the women were nulliparous and delivered at term at the time of first delivery. The first pregnancy delivery mode was classified as (1) vaginal delivery, (2) antepartum cesarean delivery (CD) without labor, or (3) intrapartum CD after the onset of labor. Within these three groups, rates of placenta previa, placenta accreta/increta, and significant PPH at the time of the second delivery were compared. Significant PPH was defined as hemorrhage requiring a blood transfusion. A total of 8208 women were analyzed. Most first deliveries were vaginal ( = 5210, 63.5%), followed by antepartum CD ( = 2432, 29.6%) and intrapartum CD ( = 566, 6.9%). The incidence of placenta previa in subsequent deliveries differed by previous delivery mode: vaginal, 0.9%; antepartum CD, 2.0%; intrapartum CD, 1.6% ( < .001). Similar differences were also observed with respect to placenta accreta/increta (0.5 versus 1.5 versus 0.9%,  < .001) and PPH (0.6 versus 1.2 versus 0.4%,  = .017). Compared to the previous vaginal delivery group, the antepartum CD group had increased risks of placenta previa (aORs 2.02, 95% CI 1.35-3.05), placenta accreta/increta (aOR 2.52; 95% CI 1.53-4.14) and PPH (aOR 1.78, 95% CI 1.14-2.98) in subsequent pregnancies. However, the previous intrapartum CD was not significantly associated with increased risks of these complications. Previous antepartum CD was associated with two-fold increased risks of placenta previa, placenta accreta/increta, and significant PPH in the second delivery compared to women with a prior vaginal delivery. The increased risks of subsequent abnormal placentation following primary antepartum CD may be important for counseling concerning nonmedically indicated elective cesarean. Previous antepartum cesarean delivery (CD) was associated with two-fold increased risks of placenta previa, placenta accreta/increta, and significant PPH in the second delivery.