By AMERICAN HEART ASSOCIATION NEWS

Studies have shown strong links between preterm births and future health risks such as heart failure. But being born early, yet still within the full-term range, may also pose heart-related risks later in life, a new study suggests.

The findings could have far-reaching implications in terms of helping to shape public health policies regarding avoidable early deliveries.

A full-term pregnancy traditionally refers to one that lasts between 37 and 42 weeks. But the new study, published Wednesday in the Journal of American Heart Association, found that babies born at 37 to 38 weeks of pregnancy had worse cardiorespiratory fitness as teens and young adults than those born at 39 to 42 weeks.

Cardiorespiratory fitness is a key measure of cardiovascular health that reflects the ability of the circulatory, respiratory and muscular systems to supply oxygen to the muscles during physical activity. Low cardiorespiratory fitness is strongly linked to a higher risk of cardiovascular disease and mortality.

An increase in early-term births, mainly due to an increase in planned deliveries through labor induction or caesarean section, has raised concerns about health and morbidity risks.

“Not all early-term deliveries can or should be prevented, for instance, if due to obstetric reasons, but there’s an increase in rates of earlier deliveries of babies without medical indication, particularly in the private sector, and this is worrisome in view of their potential lifelong impact on offspring health,” said the study’s lead researcher Isabel Ferreira, Ph.D., an associate professor of epidemiology at the University of Queensland’s School of Public Health in Australia.

Researchers examined data from 791 young people from Northern Ireland who were born between 37 and 42 weeks. Their cardiorespiratory fitness was determined at ages 12, 15 and 22.

The study found that those born between 37 and 38 weeks faced a 57 percent higher risk of developing poor cardiorespiratory fitness between childhood and young adulthood compared to those born at 39 to 42 weeks. For each extra week of gestational age, the risk of poor cardiorespiratory fitness declined by 14 percent.

The results support theories that earlier births may interrupt development and lead to permanent changes in tissues and organs that result in long-term health impairments, such as poor motor coordination and poor cardiorespiratory fitness — and thereby metabolic and cardiovascular diseases later in life.

“The researchers’ findings are consistent with notions that intrinsic factors predict cardiorespiratory fitness,” said Robert Ross, Ph.D., a professor at Queen’s University School of Kinesiology and Health Studies in Kingston, Canada, who co-chaired a 2016 American Heart Association scientific statement on the importance of assessing cardiorespiratory fitness in clinical practice.

“It makes sense that gestational age is one of the factors that could explain inherent differences in CRF,” said Ross, who was not involved in the study.

Ross noted that the study didn’t mention whether participants’ higher cardiorespiratory fitness levels was because they were more physically active. But he said that may not affect the study’s conclusions.

“Babies born at 37 to 38 weeks might not be as OK as we thought,” Ferreira said. “We need to inform medical professionals and mothers of the lifelong health risks. This information can help design policies to prevent unnecessary early-term deliveries.”

Children participating in the Northern Ireland Young Hearts Project perform the 20-meter shuttle run fitness test accompanied by a member of the research staff. (Photo courtesy of Colin A. Boreham, Ph.D.)

Children participating in the Northern Ireland Young Hearts Project perform the 20-meter shuttle run fitness test accompanied by a member of the research staff. (Photo courtesy of Colin A. Boreham, Ph.D.)

Although study participants lived in Northern Ireland, she expects findings would be similar in many other countries, including the United States and Australia, where rates of early-term births have increased. In the U.S., a 2011 study found that the percentage of early-term births rose from 22 percent in 1995 to 29 percent in 2006.

Ferreira said further research is needed on long-term health outcomes related to different gestational ages of full-term births.

She and other researchers plan to expand their analyses by pooling information from different groups worldwide on gestational age, maternal age and delivery modes to look at the trajectory of cardiorespiratory fitness and other cardiovascular risk factors over time.

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