We collected the data of 4490 pregnancies complicated with PP in two tertiary hospitals, and we observed a high association between adverse pregnancy outcomes and the type of PP. According to the traditional classification method, we found that complete and low-lying PP were the most and least dangerous types, respectively. Moreover, there were not much differences between marginal and partial PP with regard to their effects on maternal and perinatal outcomes (Tables 2 and 3). We found that the effects of the four-classification method and three-classification method of PP on maternal and perinatal outcomes were clinically similar (Tables 2–5). We also used the two-classification method from AIUM, which combined marginal, partial, and complete PP into PP. We found that PP increases the risk of PAS, PPH, hemorrhagic shock, severe PPH, blood transfusion, hysterectomy, puerperal infection, preterm labor, admission to NICU, and low birth weight (Tables 6 and 7). As per the two-classification method, PP conferred additional risks of marginal and partial PP on adverse pregnancy outcomes.
In line with our study, several studies have suggested that complete PP might be clinically different from incomplete PP, and that the former is associated with the highest risk of worsening maternal and perinatal complications[12, 13] [14]. Similar characteristics were observed between women with marginal and partial PP in the study by Dola et al., implying that they might be clinically similar to each other and different from complete PP[15]. However, Daskalakis et al. found that the type of PP did not influence the maternal and neonatal outcomes, except that neonates born to women with incomplete PP had lower Apgar scores than those of neonates born to women with complete PP[16]. Gorodeski and Bahari reported no difference between antepartum, intrapartum, or postpartum bleeding in different types of PP. They also noted that the gestational age, birth weight, and neonatal and perinatal mortality rates were similar among women with all types of PP[17].
In this study, the incidence of low-lying, marginal, partial, and complete PP was 10.38%, 27.46%, 3.12%, and 59.04%, respectively. In the study by Dola et al., a total of 179 patients had PP, out of whom 37 (21%), 21 (12%), and 117 (67%) patients had marginal, partial, and complete PP, respectively[10]. The study by Daskalakis et al. included 132 singleton pregnancies with PP, out of which 51.5% had complete PP, 20.5% had partial PP, 5.3% had marginal PP, and 22.7% had low-lying PP[16]. Initially, PP was distinguished by visual inspection or gentle palpation of the placental edge in a partly dilated cervix during labor[18]. With the advent of ultrasound, especially transvaginal ultrasound, PP was diagnosed mainly by ultrasound rather than by palpation. During mid-pregnancy, placental location was one of the routine parameters observed by ultrasound. However, it was technically difficult to differentiate between marginal and partial PP by ultrasound examination, especially as the opposite side of the internal cervical os could not be visualized on ultrasound[7]. Dashe et al.[19] reported an inability to precisely classify partial PP, especially in the absence of complete cervical dilation. Thus, whether the traditional classification is currently practical is debatable.
In the present study, we found that as per traditional classification, compared with low-lying PP, both marginal and partial PP increased the risk of PPH, blood transfusion, preterm labor, admission to NICU, and low neonatal birth weight. To further confirm that there was no clinical difference in the adverse pregnancy outcomes of women with marginal and partial PP, we considered women with marginal PP as the reference group (Table 2). We observed that partial PP did not increase the risk of adverse pregnancy outcomes, except that compared with women with marginal PP, those with partial PP showed increased risks of preterm labor and low neonatal birth weight. Owing to the technical difficulty of ultrasound in distinguishing marginal and partial PP, we proposed the three-classification method, which combines partial and marginal PP into one type, namely “marpartial” PP. As shown in Tables 2–5, the three-classification method was clinically similar to the four-classification method in investigating the effect of different types of PP on adverse pregnancy outcomes.
According to the two-classification method, low-lying PP, and marginal and partial PP afford similar risks of PAS, sever PPH, hemorrhagic shock, and hysterectomy; however, this is not true (Tables 2, 4, and 6). Adopting this method would lead to wastage of medical resources, and would require more experienced clinicians, more blood, and more women would have to undergo hysterectomy. This could increase anxiety and tension among pregnant women, which is detrimental to good pregnancy outcomes. Hence, the three-classification method is preferred to the two-classification method.
Our study offers several strengths. The relatively large sample size, including 4490 singleton pregnancies complicated with PP from two tertiary hospitals of different provinces enabled us to estimate the effect of different types of PP on adverse pregnancy outcomes. We first proposed the three-classification method to distinguish PP, and then used logistic regression analysis in three types of PP. Thus, the three-classification may be practical from the ultrasound and clinical perspective.
Nevertheless, our study has some limitations. One potential limitation is the possibility of selection bias, because the incidence of partial PP was 3.12% in our cohort. In addition, this was a retrospective cohort, and just distinguishing the types of PP is insufficient for accurate prediction of adverse pregnancy outcomes.