Identified risk factors account for small proportion of stillbirths
MedWire News: There are multiple risk factors associated with stillbirth, but these only account for a small amount of the risk for stillbirth, a second SCRN study has found.
Further research is needed to identify pregnancies at highest risk overall and for specific causes, write George Saade (University of Texas, Galveston, USA) and co-authors in JAMA.
As reported previously by MedWire News, the first of the Stillbirth Collaborative Research Network Group (SCRN) studies published in the same journal found that obstetric conditions and placental abnormalities are the most common causes of stillbirth in the USA.
The authors of the current study investigated whether there was a relation between stillbirths and risk factors that could be ascertained at the start of pregnancy, and the contribution of these risk factors to racial disparities.
They conducted a population-based, case-control study between March 2006 and September 2008, involving 59 tertiary care and community care hospitals, with access to at least 90% of deliveries within five catchment areas defined by state and county lines in the USA.
The analysis included 614 cases with deliveries of one or more stillborn fetuses and a representative sample of 1816 control deliveries of only liveborn infants, oversampled for those at less than 32 weeks' gestation and those of African descent.
Multivariate analysis revealed that mothers of nonHispanic-Black race/ethnicity, those with diabetes, and those aged 40 years or older had a 2.12-fold, 2.50-fold, and 2.41-fold higher risk for stillbirth, respectively, compared with mothers of nonHispanic-White race/ethnicity, without diabetes, or those aged 20-34 years.
In addition, mothers with AB blood types, a history of drug addiction, and who smoked less than 10 cigarettes a day during the 3 months prior to pregnancy had a 1.96-fold, 2.08-fold, and 1.55-fold increased risk for stillbirth, respectively, compared with mothers with O blood type, never used drugs, and those who never smoked.
Mothers who were overweight (25.0-29.9 kg/m2) or obese (30-34 kg/m2) had a 1.72-fold higher risk for stillbirth than those of normal weight (18.5-24.9 kg/m2), and those who did not live with a partner were 1.62 times more likely to have a stillbirth than those who were married.
Further analysis revealed that previous stillbirth and nulliparity with and without a history of prior spontaneous losses at less than 20 weeks' gestation had an almost six-fold increased risk for stillbirth compared with multiparous women without stillbirth or previous losses.
However, these risk factors explained little of the burden of stillbirth as shown by the low R2 value, a measure of variance, of 0.19, note the authors.
"Although some of the risk factors may not be modifiable (eg, race/ethnicity), knowledge of interactions between these factors and other modifiable ones may be useful," they write.
In a related commentary, editorialists Jay Iams and Courtney Lynch (The Ohio State University, Columbus, USA) write: "The reports from the SCRN will not only further the understanding of stillbirth but should also encourage the need to reframe thinking about how to address the problem of spontaneous preterm birth and the associated racial/ethnic disparities."