Health Status, Not Age, Associated with Rise in Adverse Pregnancy Outcomes in the US

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Increasing rates of adverse pregnancy outcomes (APOs) in the US, including hypertensive disorders of pregnancy (HDP), low birthweight (LBW), and preterm birth (PTB), over the last decade are largely attributable to a woman’s health status before she gets pregnant, rather than age, according to new research.

Findings from the study—to be presented at the American College of Cardiology’s (ACC) 72nd Annual Scientific Session Together with the World Congress of Cardiology, being held March 4-6, 2023, in New Orleans—showed that while the average age of pregnant persons increased from 27.9 years in 2011 to 29.1 years in 2019, age accounted for a small portion of the marked increase in APOs seen during the same period.

The greatest increase in APOs was for HDP rates, which rose by more than 50% between 2011 and 2019, yet the shift in age distribution of women giving birth accounted for less than 2% of that change, according to the study abstract.

“Although mothers are getting older at the time they deliver, that is not what’s causing these adverse birth outcomes,” said lead author Zachary Hughes, MD, an internal medicine physician at Northwestern Memorial Hospital in Chicago, in an ACC press release. “What’s really driving it is pre-pregnancy health issues like diabetes and hypertension. That’s important to know because these are factors we could potentially modify.”

Hughes and colleagues aimed to understand the contribution of changes in maternal age compared with age-specific risk of APOs. Researchers included all persons with a live birth in the US in 2011 (N=3 942 006) and 2019 (N=3 736 144) from the National Center for Health Statistics Natality Files.

According to the study abstract, investigators calculated the rate of each APO per 1000 live births, change in relative rates, and absolute change between 2011 and 2019. Then, the research team utilized a Kitagawa analysis to decompose the change in the rate of APOs into 2 parts: change in maternal age distribution and change in age-specific rate of APO.

Results

From 2011 to 2019, the mean age of birthing individuals increased from 27.9 years to 29.1 years. APO rates increased and rose most significantly for HDP (rate ratio [RR] 1.52, 95% CI, 1.51-1.53), while increases for PTB (RR 1.04, 95% CI, 1.04-1.05) and LBW (RR 1.03, 95% CI, 1.02-1.03) were more modest.

Changes in age distribution accounted for only 2% of the increase in HDP while age-specific rates were associated with 98% increase. Similar patterns were observed for LBW and PTB, according to the abstract.

Across all age groups, women who gave birth in their late teens to early thirties experienced the steepest increases in APOs. More research is needed to determine which specific health issues—such as obesity, diabetes, hypertension, or other factors—are driving these pregnancy complications in younger women, noted researchers.

“I hope these findings can lead more toward a culture change of focusing on health before pregnancy,” said Hughes. “A lot of people don’t establish care with a physician until they get pregnant, but really starting six months or a year before you’re starting to plan a pregnancy, that’s the time to maximize your health as much as possible and minimize the risk of adverse pregnancy outcomes. This also suggests that clinicians and policymakers could put more focus on pre-pregnancy health and managing things like hypertension and diabetes before someone gets pregnant.”

Hughes will present the study, “Association Between Changes in Age Distribution of Birthing Individuals and Adverse Pregnancy Outcomes in the United States, 2011-2019,” in a digital-only format that can be accessed through the ACC.23/WCC eAbstracts site beginning at 8:30 am /14:30 UTC on Saturday, March 4, 2023.