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Babies born to mothers with obesity had a higher risk of sudden unexpected infant death (SUID) compared with those born to moms with normal body mass index (BMI), according to a nationwide observational study.

In adjusted analyses, approximately 5.4% of SUID cases were attributable to maternal obesity, Darren Tanner, PhD, of Microsoft's AI for Good Research Lab in Redmond, Washington, and colleagues reported in .

Risk of SUID rose with increasing prepregnancy obesity severity, they found:

• Class I obesity (BMI 30.0-34.9): aOR 1.10, 95% CI 1.05-1.16
• Class II obesity (BMI 35.0-39.9): aOR 1.20, 95% CI 1.13-1.27
• Class III obesity (BMI ≥40.0): aOR 1.39, 95% CI 1.31-1.47

However, the absolute increase in risk wasn't large, with SUID rates ranging from 0.74 per 1,000 live births for babies born to normal weight mothers to 1.47 per 1,000 live births among mothers with class III obesity.

"It's when we consider the high and growing rates of obesity at a population scale that the risk adds up. That's where the major impact is," Tanner told MedPage Today.

Maternal obesity is on the rise, his team noted. It's a known risk factor for general infant mortality as well as a slew of maternal and infant health complications, but there has been limited research on its impact on SUID.

"This study now shows us that we can add SUID to the list of potential complications of obesity," Tanner told MedPage Today, adding that the team also recommends "that obesity be added to the list of known risk factors for SUID."

Despite the robust dose-response association between maternal BMI and SUID, more research is needed to figure out the causal mechanism, the researchers cautioned. "Some reviews have suggested that maternal obesity increases SUID risk while bed sharing," they wrote, noting, however, that this is based on a small number of case reports.

Another potential mechanism, they wrote, is that obese mothers are more likely to have obstructive sleep apnea (OSA), which is tied to negative outcomes including preeclampsia, postpartum hemorrhage, preterm birth, and more. OSA hypoxia could have detrimental effects on fetal growth, which may increase the postnatal risk of neurodevelopmental and cardiometabolic disorders "which could cause an arousal defect, thus increasing the infant's risk of death," they wrote.

In an accompanying editorial, Jacqueline Maya, MD, of Harvard Medical School in Boston, and colleagues said they "believe the evidence from this study ... is a call to action for the scientific and medical community to better understand the complex interplay of biological, social, and behavioral factors that may lead to SUID, a devastating complication that no family should experience," the editorialists wrote.

They noted that the underlying mechanisms are unlikely to be influenced directly by BMI itself "but rather the dysmetabolism related to obesity including inflammation, insulin resistance, and abnormal lipid metabolism that can affect placental biology and/or offspring early life development." Figuring out those pathways "may yield better and potentially more targeted risk-reduction strategies than prepregnancy weight loss itself," the group wrote.

They encouraged clinicians to focus on "proven interventions such as family education and counseling on safe sleep practices and reducing exposure to smoking" rather than just weight loss.

For this study, authors used data from the CDC's National Center for Health Statistics on linked birth-infant death records from 2015 to 2019. All of the live births analyzed were at 28 weeks' gestation or later; deaths were included from 4 to 364 days after birth. Cause of death codes included in the analysis were SUID, ill-defined and unknown cause, or accidental suffocation and strangulation in bed.

Of the nearly 19 million live births in the study period, 16,545 died of SUID. Mean maternal age was 29 and mean paternal age was 31. On average, infants were born at 39 weeks' gestation.

The researchers noted that the study's major limitation was lack of direct measures of sleep apnea or bed sharing, which some have theorized is a contributing factor based on limited data.

Other recent research found that multiple unsafe sleep factors were present in most cases of SUID and that more than half were sleep-surface sharing.

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