Race and Medicine

Race and Medicine

Disclosures: Bao reports no relevant financial disclosures.
November 11, 2020
3 min read

Prepregnancy obesity may increase risk for preterm birth for Asian Americans

Disclosures: Bao reports no relevant financial disclosures.
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Asian American mothers with prepregnancy overweight or obesity, defined by Asian-specific BMI cutoffs, were more likely to have a preterm birth than mothers with a normal BMI, according to findings published in the Journal of Diabetes.

Wei Bao

“Asians constitute approximately 60% of the world’s population,” Wei Bao, MD, PhD, assistant professor of epidemiology at the University of Iowa College of Public Health, told Healio. “The Asian American population is one of the fastest-growing subpopulations in the United States, increasing more than four times faster than the total U.S. population. However, there is a paucity of information concerning prepregnancy obesity and its effects in the Asian American population. Our study, using the Asian-specific BMI cutoffs, clarified the association between prepregnancy BMI and preterm birth among Asian Americans, which provided important evidence for tailored clinical recommendations for pregnant women of this race.”

Pregnant woman
Source: Adobe Stock

Asian-specific BMI categories

Bao and colleagues analyzed National Vital Statistics System data from 1,081,341 Asian American mothers who had a live singleton birth from 2014 to 2018. Prepregnancy weight and height were self-reported, and prepregnancy BMI was calculated by staff at the National Center for Health Statistics. Researchers grouped participants into six BMI categories based on Asian-specific cutoffs: underweight (< 18.5 kg/m2), normal weight (18.5-22.9 kg/m2), overweight (23-27.4 kg/m2), class I obesity (27.5-32.4 kg/m2 ), class II obesity (32.5-37.4 kg/m2) and class III obesity ( 37.5 kg/m2).

Gestational age was calculated by obstetric estimate of gestation at delivery. A preterm birth was any birth at a gestational age of less than 37 weeks. Preterm births were placed into three groups: extreme preterm for birth at less than 28 weeks of gestation, very preterm for birth at 28 to 31 weeks and moderately preterm birth at 32 to 36 weeks. Researchers also separated participants into three groups based on country of origin. The East Asian group included those of Chinese, Korean and Japanese descent; the Southeast Asian cohort included those with Vietnamese and Filipino backgrounds; and the South Asian group was for participants of Indian descent.

Prepregnancy obesity linked to preterm births

Of the study cohort, there were 70,434 preterm births. Using the Asian-specific BMI cutoffs, 7.98% of the total study cohort was classified as underweight, 31.14% as overweight, 11.79% as class I obese, 3% as class II obese and 0.88% as class III obese.

Mothers with underweight (adjusted OR = 1.04; 95% CI, 1.01-1.07), overweight (aOR = 1.18; 95% CI, 1.16-1.2), class I obesity (aOR = 1.41; 95% CI, 1.37-1.44), class II obesity (aOR = 1.69; 95% CI, 1.63-1.76) and class III obesity (aOR = 1.78; 95% CI, 1.66-1.9) had higher risks for preterm birth compared with participants in the normal-weight group. Similar associations were found when extreme, very, and moderately preterm birth outcome was examined, except there was no significant association between the underweight cohort and extreme preterm births or very preterm births.

“Using the Asian-specific BMI cutoffs (23 kg/m2 for overweight and 27.5 kg/m2 for obesity) vs. the general BMI cutoffs (25 kg/m2 for overweight and 30 kg/m2 for obesity), we found an extra 17.4% of Asian American mothers would be classified as overweight or obesity before pregnancy,” Bao said. “When these women were assessed during prenatal care for their risk of preterm birth, their true risk would have been underestimated if the general BMI cutoffs were applied. Therefore, it is critical to use Asian-specific cutoffs for Asian Americans in clinical practices to promote the health among this population.”

The risk for preterm birth varied based on country of origin. East Asian mothers had a higher risk for preterm birth with class II obesity (aOR = 1.95; 95% CI, 1.74-2.18) or class III obesity (aOR = 1.96; 95% CI, 1.57-2.44) than the Southeast Asian or South Asian groups. Of the three groups, Southeast Asians had the highest risk for preterm birth with overweight (aOR = 1.21; 95% CI, 1.17-1.26) and class I obesity (aOR = 1.55; 95% CI, 1.48-1.63). The South Asian group had lower ORs in all four categories than East Asians and Southeast Asians, but there was still an elevated risk for preterm birth with overweight and obesity when compared with women in the normal-weight category.

“Replication of the findings is needed in future studies in Asian countries,” Bao said. “Given that Asians are a heterogenous population (eg, East Asians and South Asians are different), further investigation among subpopulations of Asians may be needed.”

For more information:

Wei Bao, MD, PhD, can be reached at wei-bao@uiowa.edu.