Incidence and recurrence rate of placental abruption: a longitudinal linked national cohort study in the Netherlands




Materials and Methods


This study was performed in a retrospective nationwide cohort with the use of the Netherlands Perinatal Registry (PRN). The PRN consists of prospectively collected population-based data that contain information on pregnancies, deliveries, and (re)admissions until 28 days after birth. The database is obtained by a validated linkage of 3 different registries: the midwifery registry, the obstetrics registry, and the neonatology registry of hospital admissions of newborn infants.


The coverage of the PRN registry is approximately 96% of all deliveries in the Netherlands, and it contains all pregnancies that ended in live births and stillbirths at >22 weeks of gestation and a birthweight of at least 500 g. Furthermore, all admissions to the neonatology care unit are registered until 28 days after birth. It is used primarily for annual assessment of the quality indicators of obstetric care.


The records included in the PRN registry are entered at child’s level. There is no unique maternal identifier available in the registry to follow up on outcomes of subsequent pregnancies of the same mother. Previously, a longitudinal probabilistic-linkage procedure in which records of children of the same mother are linked was performed to create a mother identifier. This resulted in a cohort of 272,551 women with complete data on first and second deliveries of the same mother. Details on this linkage procedure are described elsewhere. The data in the PRN database are anonymous; the Dutch Perinatal Registry gave their approval for the use of the data for this study (approval no. 12.71).


Inclusion and exclusion criteria


We selected all women who delivered in the Netherlands between Jan. 1, 1999, and Dec. 31, 2007. We excluded women with a multiple gestation (n = 7,472) and women with a gestational age at delivery of >42 + 6 weeks (n = 655).


Outcome measures


Our primary outcome was placental abruption. We identified all women with a placental abruption that had been registered in the PRN registry with a code for placental abruption. Codes are assigned by midwives, residents, and obstetricians based on information in the patients’ medical record. A clinical diagnosis of placental abruption is made based on a combination of the following clinical symptoms: vaginal bleeding, abdominal pain, or fetal distress and further supported by ultrasonographic findings as retro placental bleeding. After delivery, the diagnosis may be confirmed by a couvelaire uterus, gory amniotic fluid, or examination of the placenta that reveals a clot. Placental abruption primarily is documented by 2 of the care providers after delivery; there is no stratification in severity in the PRN database. In addition, all women with a positive history of placental abruption at the start of the second pregnancy were labelled as cases of placental abruption in the first pregnancy. The gestational age at delivery of the fetus was used as the gestational age of placental abruption.


Characteristics


We extracted demographic and obstetric baseline characteristics from the PRN registry as ethnicity, maternal age, socioeconomic status, pregnancy interval, hypertension, and neonatal sex. All characteristics were primarily documented by the care providers. Ethnicity was categorized into white (native Dutch and other white women) and non-white (different ethnic groups as African/Surinamese, South Asian, Moroccan and Turkish) for this study. The continuous socioeconomic status score (based on mean income level, the percentage of households with a low income, inhabitants without a paid job, and households with, on average, a low education in a postal code area) was categorized into a high, middle, and low group based on percentile ranges (≤ 25th percentile, middle, >75th percentile). Gestational age was based on last menstrual period or ultrasound measurements at <20 weeks of gestation. If the estimation by ultrasound measurement differed >6 days from the last menstrual period, then the ultrasound measurement was considered the dominant measurement. Hypertensive disorders (HTD) included chronic hypertension, pregnancy-induced hypertension, and preeclampsia. The clinical diagnosis of hypertension was made with a systolic blood pressure of ≥140 mm Hg and/or a diastolic blood pressure of ≥90 mm Hg. Preeclampsia was diagnosed with hypertension and proteinuria.


Cases of placental abruption were analyzed in total and stratified into 3 groups based on the gestational age at the time of placental abruption in the first pregnancy; early preterm (22 +0 – 31 +6 weeks of gestation), late preterm (32+ 0 – 36+ 6 weeks of gestation), and term (37+ 0 – 42+ 6 weeks of gestation).


In addition, we stratified the analysis by HTD in the first pregnancy: women with an HTD in their first pregnancy and women without an HTD in their first pregnancy.


Analysis


We calculated the incidence of placental abruption in our cohort of 1,570,635 singleton deliveries by dividing the number of placental abruptions by the total number of deliveries. We calculated the incidence per gestational week by dividing the number of placental abruptions in a particular week by the total number of deliveries in that given week.


We selected all women with a subsequent singleton delivery and compared incidence of placental abruption in a subsequent pregnancy in women with and without a placental abruption in their first pregnancy. In addition, we compared their demographic and obstetric baseline characteristics. Comparison of the baseline characteristics was by univariate analysis that was performed with the unpaired t -test for normally distributed continuous variables and with the χ 2 test for categoric variables. All tests were 2-sided with a probability value of .05 as the threshold for statistical significance.


To estimate the effect of a history of placental abruption on the occurrence of placental abruption in a subsequent pregnancy, logistic regression modeling was used and was expressed as odds ratio with a 95% confidence interval (CI). In addition, the effect of gestational age at placental abruption in the first pregnancy was estimated and expressed as odds ratio with 95% CI. To account for the effect of potential confounders, we used a multivariate logistic regression analysis to adjust for variables that were distributed unequally in the baseline characteristics. When a low incidence of placental abruption was found, Firths’ penalized likelihood approach was performed to minimize small sample size bias. Kaplan-Meier curves by gestational age of first placental abruption were constructed for the recurrent placental abruptions.


We tested for an association between placental abruption and HTD in the first pregnancy. When statistically significant, analyses were also performed separately for HTD and non-HTD cases per 3 strata of gestational age of first placental abruption. In addition, we tested for interaction between HTD in the first pregnancy and the recurrence of placental abruption in a subsequent pregnancy by adding an interaction term to our logistic regression model.


The data were analyzed with the SAS statistical software package (version 9.3; SAS Institute Inc, Cary, NC).




Results


Between Jan. 1, 1999, and Dec. 31, 2007, a total of 1,570,635 singleton pregnancies were identified; 3496 pregnancies (0.22%) were complicated by a placental abruption. The overall incidence was highest between 28 and 31 weeks of gestation, with 40.8 per 1000 deliveries (4.1%). Between 32 and 34 weeks of gestation, the incidence was 20.5 per 1000 deliveries (2.1%); between 39 and 42 weeks of gestation, the incidence was 0.8 per 1000 (0.08%; Figure 1 ).




Figure 1


Incidence of placental abruption

Graph shows the incidence of placental abruption per 1000 deliveries per gestational week of pregnancy.

Ruiter. Incidence and recurrence rate of placental abruption in singletons. Am J Obstet Gynecol 2015 .


A total of 264,424 women (528,848 deliveries) were available for the analysis of the recurrence rate and incidence of placental abruption in a subsequent pregnancy. Baseline characteristics of our linked cohort are listed in Table 1 . In the first pregnancy, 521 women (0.20%) had a placental abruption, among these women an age of <25 years, non-white ethnicity, low socioeconomic status, and HTDs were more prevalent.



Table 1

Baseline characteristics of the linked cohort

















































Characteristics of the first pregnancy Placental abruption in first pregnancy (n = 521) No placental abruption in first pregnancy (n = 263,903) P value
Maternal characteristics
Maternal age, y a 28.0 ± 4.6 28.6 ± 4.2 .0001
Maternal age <25 y, n (%) 115 (22.1) 42,784 (16.2) .0003
Mean gestational age, wk a 34.6 ± 4.3 39.2 ± 2.2 < .0001
Non-white maternal ethnicity, n (%) 74 (14.2) 28,826 (10.9) .0165
Low socioeconomic status, n (%) 149 (28.6) 57,732 (21.9) .0002
Hypertensive disorder, n (%) 147 (28.2) 33,186 (12.6) < .0001
Fetal characteristic: male, n (%) 283 (54.3) 135,887 (51.5) .1970

Ruiter. Incidence and recurrence rate of placental abruption in singletons. Am J Obstet Gynecol 2015 .

a Data are presented as mean ± SD.



Of the 521 women with a placental abruption in the first pregnancy, 30 women (5.8%) had a recurrent placental abruption in the subsequent pregnancy. Placental abruption in a subsequent pregnancy occurred in 184 parous women (0.07%) without a history of placental abruption. Figure 2 shows all women with a placental abruption in the first pregnancy and their time to a recurrent placental abruption, stratified by gestational age of the first placental abruption.




Figure 2


Recurrent placental abruption by gestational age of first placental abruption

Graph shows the time to placental abruption in a subsequent pregnancy after the first early preterm, late preterm, or term placental abruption.

PA , placental abruption.

Ruiter. Incidence and recurrence rate of placental abruption in singletons. Am J Obstet Gynecol 2015 .


After adjustment for maternal age, ethnicity, socioeconomic status, and hypertension, a placental abruption in the first pregnancy was associated with a significantly increased risk of placental abruption in a subsequent pregnancy (adjusted odds ratio, 93; 95% CI, 62–139).


Table 2 shows the distribution of placental abruption in a subsequent pregnancy in women with and without a history of placental abruption and the crude and adjusted odds ratios of placental abruption in the first pregnancy on the recurrence rate of placental abruption in a subsequent pregnancy, stratified by gestational age of first placental abruption. The odds ratio of a history of placental abruption on the recurrence in a subsequent pregnancy was higher for women with a placental abruption in the term period of the first pregnancy than for women with a previous late or early preterm placental abruption.



Table 2

Placental abruption in a subsequent pregnancy in total and by gestational age of placental abruption in the first pregnancy































































Variable Placental abruption in second pregnancy, wk Total abruption second pregnancy, n (%) Odds ratio (95% confidence interval)
22 + 0 to 31 + 6, n 32 + 0 to 36 + 6, n 37 + 0 to 42 + 6, n Crude Adjusted a
Complete cohort of women with first-term delivery, no placental abruption in first pregnancy (n = 243,799) 26 62 70 158 (0.1) Reference Reference
Complete cohort placental abruption first pregnancy (n = 521) 2 13 15 30 (5.8) 95 (64–142) 93 (62–139)
Gestational age of placental abruption in the first pregnancy
22 + 0 to 31 + 6 wk (n = 128) 1 1 1 3 (2.3) 43 (16–126) 39 (13–116)
32 + 0 to 36 + 6 wk (n = 210) 0 4 3 7 (3.3) 57 (27–120) 52 (25–111)
37 + 0 to 42 + 6 wk (n = 183) 1 8 11 20 (11) 193 (119–313) 188 (116–306)

Ruiter. Incidence and recurrence rate of placental abruption in singletons. Am J Obstet Gynecol 2015 .

a Adjusted for hypertension, maternal age, ethnicity, and low socioeconomic status.



Of the 264,424 first singleton pregnancies, a total of 33,333 women (12.6%) had an HTD. In the second pregnancy, 17,378 women (6.6%) had an HTD. In the first pregnancy, placental abruption was more prevalent in the HTD group compared with the non-HTD group (0.44% vs 0.16%; odds ratio, 2.73; 95% CI, 2.26–3.31). In the second pregnancy, placental abruption was also more prevalent in the HTD group compared with the non-HTD group (0.52% vs 0.17%).


Table 3 shows that, in both women with and without HTD in their first pregnancy, the recurrence risk of placental abruption is increased for women with a history of placental abruption compared with women without a history of placental abruption. Table 3 also shows that the odds ratio of a history of placental abruption on the recurrence risk is lower for women with an HTD in their first pregnancy compared with women who were normotensive in their first pregnancy. Although the initial risk of placental abruption is increased by the presence of an HTD, the interaction between an HTD in the first pregnancy and the recurrence risk of placental abruption in a subsequent pregnancy was not statistically significant ( P = .1).



Table 3

Placental abruption in a subsequent pregnancy by presence of hypertensive disorder in the first pregnancy































Complete cohort placental abruption first pregnancy (n = 521) Placental abruption in second pregnancy, wk Total abruption second pregnancy, n (%) Odds ratio (95% confidence interval)
22 + 0 to 31 + 6, n 32 + 0 to 36 + 6, n 37 + 0 to 42 + 6, n Crude Adjusted a
Hypertensive disorder in first pregnancy (n = 147) 0 2 4 6 (4.1) 0.66 (0.27–1.60) 0.68 (0.28–1.63)
No hypertensive disorder in first pregnancy (n = 347) 2 11 11 24 (6.9) Reference Reference

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May 5, 2017 | Posted by in GYNECOLOGY | Comments Off on Incidence and recurrence rate of placental abruption: a longitudinal linked national cohort study in the Netherlands

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