Materials and Methods
We conducted a population-based retrospective cohort study involving all singleton deliveries over 20 weeks' gestation in the province of Nova Scotia from 1988 to 1995, inclusive. Multiple births were excluded because they might result in events that are not independent of each other. Information was collected from the Nova Scotia Atlee Perinatal Database, which codes for approximately 1200 variables, including maternal and neonatal outcomes, details of medical histories, and sociodemographics. After delivery, each chart was reviewed and data abstracted by a trained health technician using the Nova Scotia Atlee perinatal database coding system, which is modified from the International Classification of Diseases code. Placenta previa was defined as a placenta that on ultrasound was low lying, that partially or completely covered the internal os of the cervix, and that was confirmed at delivery by double set-up or cesarean delivery.
Neonatal outcomes included perinatal death, congenital anomaly, birth weight, and preterm birth (defined as delivery before 37 weeks' gestation). Congenital anomalies included cardiovascular, gastrointestinal, respiratory, otolaryngologic, genitourinary (including renal), dermatologic, musculoskeletal, neurologic, and chromosomal anomalies. Various specific measures of neonatal morbidity were evaluated, including respiratory distress syndrome (RDS), respiratory depression at birth, Apgar score less than 7 at 5 minutes, intraventricular hemorrhage, anemia, and length of hospital stay. Respiratory distress syndrome was defined as the presence of grunting, retractions, and decreased air entry before 3 hours of age, persisting beyond 6 hours of age, and not explained by any other disease. It was graded as mild (less than 35% oxygen), moderate (at least 35% oxygen or continuous positive airway pressure), or severe (mechanical ventilation). Respiratory depression at birth was defined as decreased respiratory effort requiring intermittent positive pressure ventilation. Intraventricular hemorrhage included all four grades and all subependymal hemorrhages, regardless of cause or predisposing factor. Neonatal anemia was defined as hemoglobin less than 140 g/L or hematocrit less than 42% in the first week of life, or hemoglobin less than 100 g/L or hematocrit less than 30% at any neonatal age before discharge.
Data were analyzed using SAS 6.11 (SAS Institute Inc, Cary, NC) statistical program to compare women with placenta previa to women without placenta previa who delivered in the same period. Continuous variables are given as median (not a normal distribution) and compared using the Wilcoxon rank sum test. Categoric variables are given as a percentage and compared using χ2 or Fisher exact test where appropriate. Categoric variables are also given as and compared using crude odds ratios (OR) and 95% confidence intervals (CI). When neonatal complications other than mortality and major anomaly were examined, stillbirths were excluded (because neonatal complications would not be possible in that group). Multiple logistic regression was used to control for potential confounders, providing adjusted ORs.
During the 8 years of observation, 92,983 women delivered singletons, 305 of whom were coded for placenta previa, a prevalence of 0.33%. Perinatal death (stillbirth and neonatal death) occurred in 2.30% of pregnancies complicated by placenta previa, compared with 0.78% of those without placenta previa (Table 1). The crude OR suggested an increased risk of perinatal death with placenta previa, but when adjustments were made for maternal age, gestational age, and congenital anomalies, the risk of death was no longer significantly increased (Table 2). Placenta previa was significantly associated with major fetal anomalies, even when adjusted for maternal age.
After adjustment for potential confounders (Table 2), the significant neonatal complications included RDS and anemia. Potential complications not found to be significant after controlling for the same potential confounders included respiratory depression at birth, intraventricular hemorrhage, and a low Apgar score at 5 minutes. As expected, preterm births and neonatal intensive care unit (NICU) admissions were significantly more frequent in the placenta previa group. Neonatal hospitalizations were longer in that group. Birth weights were lower in the study group, but were not significantly different when adjusted for gestational age (P = .15).
The frequency of perinatal death in this study was less than that reported in earlier studies (2.30% versus 3.6–37%),1–3,5–7,14–16 which might be explained by advances in obstetric and neonatal treatment during the past 10 years. Although perinatal death was more frequent in pregnancies complicated by placenta previa than in other gestations, the relationship became insignificant when maternal age, gestational age at delivery, and congenital anomalies were controlled. Some investigators suggested an association between placenta previa and congenital anomalies,3 but they did not control for maternal age. Other investigators did not observe that association.6,7,16 The association between placenta previa and congenital anomalies was supported by the present study, even after controlling for maternal age. This finding might be important when assessing and counselling patients with placenta previa; however, the mechanism of the association is not known.
Other neonatal complications associated with placenta previa in previous studies include preterm birth, low birth weight, respiratory depression at birth, RDS, intraventricular hemorrhage, anemia, and low Apgar scores.2,3,5–7,14–19 None of those studies controlled for maternal age, gestational age, and congenital anomalies. When potential confounders were controlled for, neonatal complications of placenta previa included RDS and anemia. It might be that the circumstances of the deliveries of those infants (bleeding with or without fetal compromise) predisposed them to hypoxia and anemia, thus increasing the incidence of RDS.5 The present study confirmed that preterm birth, admission to NICU, and length of neonatal hospital stay were significantly increased in pregnancies complicated by placenta previa. After controlling for gestational age, birth weight did not appear to be adversely influenced by placenta previa. That finding contradicts previous studies that suggested a higher incidence of suspected fetal growth restriction1,15,17,18 and might be explained by improvements in obstetric ultrasound and treatment.
Our study took place when transvaginal ultrasound, maternal steroids for lung maturity, and neonatal surfactants were available. The perinatal mortality rate was lower than that in previous studies, and infants were more likely to be preterm but not growth delayed when gestational age was considered. Because our findings incorporated current obstetric and neonatal practices, knowledge of neonatal complications of placenta previa can be used to improve prenatal counseling and neonatal treatment.
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