Large birth weight on the decline in the U.S.

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Public health researchers have found that the rate of large fetal birth weight in the U.S. has declined over the past five decades, with the largest drop observed in infants who are labeled among the most severe and lethal cases.

USF College of Public Health alumnae Drs. Lindsey King, a clinical assistant professor in the College of Public Health and Health Professions at the University of Florida, and Korede Yusuf, assistant professor in the College of Nursing and Public Health at Adelphi University, along with Dr. Abraham Salinas-Miranda, associate director of the COPH’s Center of Excellence in Maternal and Child Health and director of the Harrell Center for the Study of Family Violence and associate director for the USF Center for Excellence in Maternal and Child Health, were part of  a research team that conducted the largest population-based study examining fetal macrosomia.

Fetal macrosomia is defined as a birth weight greater than or equal to 8.818 pounds, regardless of gestational age.

(Photo source: Pixabay)

King says that studies worldwide have reported an increase of macrosomia over several decades and that the prevalence of obesity among pregnant women in the U.S. is also on the rise.

“Previous studies have shown an association between obesity and an increased risk of fetal macrosomia, which is also associated with an elevated risk of infant and maternal morbidity and mortality,” Salinas-Miranda said.

Their research, “Trends in the incidence of fetal macrosomia and its phenotypes in the United States, 1971–2017,” which was published in Archives of Gynecology and Obstetrics, aimed to examine trends in fetal macrosomia in the U.S. among singleton live births.

Conducting a population-based retrospective cohort study for the past five decades, they looked back on natality data files on all U.S. live births from 1971 to 2017 complied by the National Center for Health Statistics and made publicly available by the CDC.

They also broke down the cases of macrosomia into three phenotypes based on weight, creating a continuum of risk‑‑‑with greater risk of complications occurring with each ascending range of values.  

They segmented the cases as such: Grade 1 = 8.818 – 9.919 lbs.; Grade 2 = 9.920 – 11.021 lbs.; and Grade 3 = ≥ 11.022 lbs.

“Our study is the most recent analysis of trends of fetal macrosomia in the U.S. and the largest population-based study conducted regarding fetal macrosomia, covering almost half a century,” King said.

They found that the risk of infant morbidity increased substantially with birth weights greater than 9.920 lbs. and the risk of infant mortality increased even more significantly with birth weights greater than 11.022 lbs.

Drs. Lindsey King, Korede Yusuf, and Abraham Salinas-Miranda presenting their research findings at the 2019 American Public Health Association conference in Philadelphia. (Photo courtesy of King)

“It is useful to assess temporal trends in macrosomia taking into account these phenotypes that exhibit different risk profiles,” King said. “Our study found that the most pronounced decline in rate of macrosomia occurred in Grade 3, the most severe and lethal phenotype.”

Overall, though, they found that from a baseline rate of 8.84 percent, the rate of fetal macrosomia declined to 8.07 percent at the end of the study, representing a drop of 8.7 percent.

“This decline was also noted in each of the three phenotypes, with the greatest drop among infants with Grade 3 macrosomia, the most servere and lethal phenotype,” King said. “The most impactful factors were maternal age and gestational weight gain.”

They hope to take this research a step further to examine what impact planned deliveries of diabetic pregnancies has on the potential benefit to reduce excessive fetal weight gain.

“It has not been established whether the earlier delivery and thus lesser weight will prevent birth-related complications in those infants,” King said. “We would love to examine this in future studies.”

Story by Anna Mayor, USF College of Public Health