Obstetric risk factors associated with placenta previa development: case-control study

To evaluate potential risk factors and perinatal outcome of pregnancies complicated with placenta previa in Croatian population of pregnant women recruited from the largest tertiary care perinatal center in Croatia.

This retrospective case-control study included a total of 202 singleton pregnancies with placenta previa during a 10-year study period and 1,004 randomly selected simple singleton controls. Data on potential risk factors for placenta previa development were carefully extracted from medical records, reviewed, and compared with a control group of women. Data were statistically analyzed with chi-square test and Mann-Whitney U test, and crude odds ratio (OR) with 95% confidence interval (95% CI) were provided.

The incidence of placenta previa was 0.4%. Factors significantly associated with a placenta previa development were advanced maternal age (especially >34 years, even after adjustment for high parity), gravidity of 3 and more (OR, 4; 95% CI, 2.5-6.6), more than one previous delivery (OR, 2.76; 95% CI, 1.7-4.3), history of previous cesarean sections (OR, 2.0; 95% CI, 1.17-3.44), abortions (OR, 2.8; 95% CI, 2.04-3.83), and presence of various uterine abnormalities (OR, 8.5; 95% CI, 1.75-44.5). The risk was significantly increased after two previous cesarean sections (OR, 7.32; 95% CI, 2.1-25) and after one previous abortion (OR, 4.8; 95% CI, 2.7-8.3). No difference between the groups was found regarding the history of previous placenta previa, drug abuse, and male sex at birth. Smoking history was significantly less frequent in women with placenta previa than controls (16.3% vs 25.6%, chi-square=7.9, p=0.007). The main perinatal complication was preterm birth, with 14-fold higher risk in women with placenta previa. Preterm infants of mothers with placenta previa were more likely to have lower first- (6 vs 10, p<0.001) and fifth-minute median Apgar scores (8 vs 10, p<0.045). Term infants of mothers with placenta previa had significantly lower birth weight then their controls (3,300 vs 3,500 g, p<0.001).

The most important obstetric factors for placenta previa development were advanced maternal age especially >34 years, 3 or more previous pregnancies, parity of 2 and more, rising number of previous abortions, and history of previous cesarean section, but not child sex at birth, history of drug abuse and previous placenta previa. Smoking cigarettes was significantly less frequent in women with placenta previa. Preterm delivery still remains the greatest problem in pregnancies complicated with placenta previa.