(Reuters Health) - Babies born a little early, but still within the range considered “full term,” may have worse cardiorespiratory fitness than peers born after a full 39 weeks of gestation, suggests a recent study.

Cardiorespiratory fitness reflects the body’s ability to supply oxygen to muscles during physical activity. It also affects metabolic and cardiovascular health, the study authors note in the Journal of the American Heart Association.

“There is an increasing trend toward earlier deliveries of babies that can be almost fully attributed to an increase in rates of induced or caesarian section deliveries after 37 weeks but before 39 completed weeks of gestation, when not medically necessary (i.e. elective/planned deliveries),” lead author Isabel Ferreira told Reuters Health by email.

“It is becoming increasingly evident that shorter gestation, even within the at-term period, may lead to higher rates of adverse health outcomes, such as respiratory and neurological morbidity and mortality in neonates and infants,” said Ferreira, a researcher at The University of Queensland in Brisbane, Australia.

Poor cardiorespiratory fitness is a major determinant of metabolic and cardiovascular health during youth and later in life, as well as a strong determinant of individuals’ longevity, Ferreira said.

The researchers looked at data from the Northern Ireland Young Hearts Project, a study that followed the development of cardiovascular risk factors through adolescence to young adulthood. They also had data on the participants’ gestational age at birth and maternal health and habits.

The study team included 791 participants born within the full-term range of 37-42 weeks of gestation. Their cardiorespiratory fitness was determined at ages 12, 15 and 22 years by measuring their maximal oxygen uptake level after undergoing standardized physical tests.

Compared to kids born at full-term (39-40 weeks) and late-term (41-42 weeks), those born early-term (37-38 weeks) were about 57 percent more likely to have poor cardiorespiratory fitness during adolescence and young adulthood, the study found.

This was true after researchers adjusted for a variety of other factors that could influence fitness, such as age, weight, diet, physical activity, smoking behavior, maternal health and smoking and household income.

In addition, researchers found that each week of increase in gestational age was associated with a 14 percent reduction in risk for poor cardiorespiratory fitness.

The study team notes that early births may interrupt normal development of the lungs and other organs that would take place in the final few weeks of pregnancy.

“Of course, not all early term deliveries can be prevented, for instance, if due to obstetric reasons or if they occur spontaneously. But those earlier deliveries that are planned without medical indication could be prevented in view of their potential lifelong impact on the offspring health,” Ferreira said.

In other words, mothers and healthcare providers should be informed of the lifelong health risks that early-term deliveries may have on their offspring, and refrain from these unless there is a medical indication to anticipate deliveries, she added.

“I think it tells us again that those weeks in utero are active, and things are happening, but I think that it needs to be validated with other information,” said Dr. Mary Ann Bauman, a primary care physician and women’s health advocate in Seattle, who wasn’t involved in the study.

“It’s emerging science we don’t know how valid it is. But I think if women have a choice, they’re always anxious to get their last few weeks of pregnancy over. It’s the time when you’re feeling large and uncomfortable etc, there may be some benefit to waiting a bit longer,” she said.

Bauman added that she doesn’t want to scare women who for whatever reason need to have a birth induced early. The authors of the study point out, she added, that exercise can improve cardiorespiratory fitness.

“The American Heart Association is recommending that we start with exercise early in life,” Bauman said.

SOURCE: bit.ly/2kIij09 Journal of the American Heart Association, online September 27, 2017.