Medline ® Abstracts for References 1-4

OBJECTIVE: To study perinatal mortality associated with placental abruption.

DESIGN: Retrospective population study using the Finnish Hospital Discharge Register and Medical Birth Register data.

SETTING: Finland, 1987-2005.

POPULATION: Pregnancies with placental abruption and all other births without placental abruption.

METHODS: The national Hospital Discharge Register and Medical Birth Register were used to identify all pregnancies with placental abruption. Demographic data and delivery outcomes were collected retrospectively. Perinatal mortality associated with placental abruption was compared with that in other births. Potential risk factors were analysed.

MAIN OUTCOME MEASURES: Perinatal mortality in placental abruption.

RESULTS: The study consisted of 618 735 women with 1.14 million pregnancies, 4336 of whom had placental abruption. Overall perinatal mortality with abruption was 119 per 1000 births. Placental abruption explained 7% of all perinatal deaths. The mortality among singleton births (125 per 1000) was higher than among multiple births (40 per 1000). The majority of deaths (77%) occurred in utero. Singleton perinatal mortality with abruption decreased from 173 per 1000 in 1987-1990 to 98 per 1000 in 2000-2005 (p<0.001). In singleton births at<32 gestational weeks, overall perinatal mortality was high (345 per 1000) and was not increased by placental abruption. Prematurity, low birthweight, male fetal sex and maternal smoking were independent risk factors for placental abruption-related perinatal mortality.

CONCLUSIONS: Although mortality associated with placental abruption decreased during the study period, placental abruption still remains an important cause of perinatal mortality.

Placental abruption is an uncommon obstetric complication associated with high perinatal mortality rates. The authors explored the associations of abruption with fetal growth restriction, preterm delivery, and perinatal survival. The study was based on 7,508,655 singleton births delivered in 1995 and 1996 in the United States. Abruption was recorded in 6.5 per 1,000 births. Perinatal mortality was 119 per 1,000 births with abruption compared with 8.2 per 1,000 among all other births. The high mortality with abruption was due, in part, to its strong association with preterm delivery; 55% of the excess perinatal deaths with abruption were due to early delivery. Furthermore, babies in the lowest centile of weight (<1% adjusted for gestational age) were almost nine times as likely to be born with abruption than those in the heaviest (>or =90%) birth weight centiles. This relative risk progressively declined with higher birth weight centiles. After controlling for fetal growth restriction and early delivery, the high risk of perinatal death associated with abruption persisted. Even babies born at 40 weeks of gestation and birth weight of 3,500-3,999 g (where mortality was lowest) had a 25-fold higher mortality with abruption. The link between fetal growth restriction and abruption suggests that the origins of abruption lie at least in midpregnancy and perhaps even earlier.

The authors use recent methodology in causal inference to disentangle the direct and indirect effects that operate through a mediator in an exposure-response association paradigm. They demonstrate how total effects can be partitioned into direct and indirect effects even when the exposure and mediator interact. The impact of bias due to unmeasured confounding on the exposure-response association is assessed through a series of sensitivity analyses. These methods are applied to a problem in perinatal epidemiology to examine the extent to which the effect of abruption on perinatal mortality is mediated through preterm delivery. Data on over 26 million US singleton births (1995-2002) were utilized. Risks of mortality among abruption and nonabruption births were 102.7 and 6.2 per 1,000 births, respectively. Risk ratios of the natural direct and indirect (preterm delivery-mediated) effects of abruption on mortality were 10.18 (95% confidence interval: 9.80, 10.58) and 1.35 (95% confidence interval: 1.33, 1.38), respectively. The proportion of increased mortality risk mediated through preterm delivery was 28.1%, with even higher proportions associated with deliveries at earlier gestational ages. Sensitivity analyses underscore that the qualitative conclusions of some mediated effects and substantial direct effects are reasonably robust to unmeasured confounding of a fairly considerable magnitude.

OBJECTIVE: To investigate stillbirth, neonatal, and perinatal death outcomes in pregnancies complicated by placental abruption, according to fetal sex.

METHODS: We utilized maternally linked cohort data files of singleton live births to mothers diagnosed with placental abruption during the period 1989 through 2005 (n = 10,014). Logistic regression models were employed to generate adjusted odd ratios and their 95% confidence intervals. Male babies served as the referent category.

RESULTS: The sex ratio at birth was 1.18. The overall prevalence of stillbirth, neonatal mortality, and perinatal mortality was 7.2%, 4.5%, and 11.8%, respectively. Placental abruption was less likely to occur in mothers carrying female pregnancies than mothers of male infants (adjusted odds ratio [95% confidence interval] = 0.89 [0.86-0.93]). There were no significant sex differences with regards to stillbirth, neonatal mortality, and perinatal mortality. Similar findings were observed for preterm and term infants.

CONCLUSIONS: Although a preponderance of male infants was discernable among mothers with placental abruption, no sex difference in fetal survival was observed among the offspring of the mothers affected by placental abruption.