Increasing maternal body mass index shows a moderate to strong dose-response relationship with increasing risks of fetal death, stillbirth, neonatal death, perinatal death, and infant death, according to a report published online April 15 in JAMA.
In what they described as the first meta-analysis to comprehensively summarize the findings regarding maternal overweight and obesity on the one hand and infant mortality risks on the other, researchers compiled data from 38 cohort studies that tallied at least three categories of maternal BMI as well as several separate infant mortality outcomes. Most of the studies were performed in Europe (19) and North America (6), but there also were 6 from Australia, 4 from Asia, 2 from Latin America, and 1 from Africa.
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The new findings suggest a dose-response relationship between maternal BMI and mortality risks in pregnancy.
Together, these studies included 10,147 fetal deaths, 16,274 stillbirths, 4,311 perinatal deaths, 11,294 neonatal deaths, and 4,983 infant deaths, and most accounted for potentially confounding factors such as maternal age, parity, and smoking status, lending this meta-analysis the statistical power to specifically quantify mortality risks, said Dagfinn Aune of the department of epidemiology and biostatistics, Imperial College London School of Public Health, and his associates.
Even modest increases in maternal BMI were linked with increases in the risk of every category of infant mortality. In a linear dose-response analysis, the relative risk ranged between 1.15 and 1.24 for every 5-unit increase in maternal BMI. "The greatest risk was observed in the category of severely obese women; women with a BMI of 40 had an approximately two- to threefold increase in the [relative risk] of these outcomes vs. a BMI of 20, with absolute risks in the range of 0.69% to 2.7% for BMI of 40 vs. 0.20% to 0.76% for BMI of 20," the investigators said (JAMA 2014 April 15 [doi:10/1001/jama.2014.2269]).
The dose-response nature of this relationship suggests an underlying biological connection between maternal adiposity and infant death. Maternal obesity is known to raise the risk of preeclampsia, gestational diabetes, type 2 diabetes, gestational hypertension, and congenital anomalies, which may in turn raise the risk of infant death. It is also associated with increased inflammatory responses, vascular and endothelial dysfunction, and altered lipid metabolism, which can in turn raise the risk of placental thrombosis, decrease placental perfusion, and lead to placental infarction or abruption in late pregnancy. Finally, maternal obesity is associated with macrosomia, which in turn is related to asphyxia, infection, and infant death, Mr. Aune and his associates said.
This study was supported by the Norwegian SIDS and Stillbirth Society. Mr. Aune and his associates reported no financial conflicts of interest.