QUEENSLAND, AUSTRALIA — Children born early term at 37 to 38 weeks of gestation are at increased risk of poor cardiorespiratory fitness (CRF) during adolescence and young adulthood relative to their peers born later term, at 39 to 42 weeks, a new study shows[1].
“The increasing trends toward earlier deliveries and the strong links between CRF and metabolic and cardiovascular health in youth and later in life support the importance of our findings,” lead author Dr Isabel Ferreira (University of Queensland, Australia), told theheart.org | Medscape Cardiology.
“Mothers and clinicians should thus refrain from planned deliveries (induction of labor or cesarean sections) before 39 weeks of gestation unless there is a medical indication to anticipate deliveries,” she advised.
The study was published online September 27, 2017 in the Journal of the American Heart Association.
Novel Study
Other cohort studies have shown that shorter gestation, even within the at-term period, may lead to adverse health outcomes, such as neonatal and infant neurological, cognitive, and respiratory morbidity and mortality. But this is the first study to examine the extent to which CRF varies across different gestational lengths within the at-term range (37 to 42 weeks) and the first to characterize such differences in CRF from childhood through adolescence to adulthood, Ferreira explained.
The researchers assessed CRF at age 12, 15, and 22 years in 791 children in the Northern Ireland Young Hearts Study who were born at different gestational ages within the at-term range. All were singleton births. CRF was estimated from field and laboratory tests and expressed by maximal oxygen uptake level through adolescence to young adulthood.
Mean levels of CRF at age 12, 15, and 22 were 45.6, 43.7, and 33.0 mL/kg per minute, respectively.
Gestational age was significantly associated with CRF through adolescence to young adulthood. For each week increase in participants’ gestational age, their CRF was 0.46-mL/min/kg (95% CI 0.14–0.79) higher, the researchers report.
After adjustment for all relevant cofactors, each week increase in gestational age correlated with a 14% relative risk reduction of poor CRF (risk ratio [RR] 0.86, 95% CI 0.76–0.96).
Notably, write the researchers, when comparing individuals according to categories of gestational age, those who born full term (39 to 40 weeks) or late term (41 to 42 weeks) had a similarly lower risk for poor CRF than those who were born early term at 37 to 38 weeks (RR 0.65 [95% CI, 0.47–0.89] and 0.59 [95% CI 0.40–0.90], respectively).
Conversely, compared with individuals born full term or late term (combined), individuals who were born early term had a 57% higher risk of poor CRF throughout adolescence to adulthood (RR 1.57, 95% CI 1.14–2.16). Diet, physical activity, and smoking behavior did alter the results.
‘Worrisome’ Trend in Early-Term Births
“We believe that earlier births—even within the at-term range—may interrupt normal development and lead to permanent changes of tissues and organs, thereby affecting cardiorespiratory fitness. As such, recent trends toward deliveries at shorter gestational lengths within the at-term period are worrisome,” Ferreira said in a news release.
“Although there are guidelines that warn against planned deliveries before 39 weeks of gestation (eg, from the American College of Obstetricians and Gynecologists), increasing rates of early-term births in countries such as the US and Australia observed over the past decades can be almost fully attributed to planned deliveries before labor,” Ferreira said.
The current study, she added, “illustrates the heterogeneity in long-term health risk by gestational age at term.”
In an interview with theheart.org | Medscape Cardiology, American Heart Association (AHA) spokesperson Dr Mary Ann Bauman called the study interesting.
“We’ve typically considered term to be a homogenous group, and this study suggests that maybe there is some heterogeneity in there in terms of development for the baby,” Bauman said.
“Women are always anxious toward the end of pregnancy to have the pregnancy end, but women will probably want to know that waiting a little longer when there is a voluntary choice is not a bad way to go because the development of that child is still occurring right up to delivery,” she said.
“I certainly don’t think this study is definitive,” she added, “and there will need to be more studies looking at this. Even if cardiorespiratory fitness is lower, moderate to vigorous exercise can overcome that, so that’s another point that says our children need to be exercising.”
The study was funded by the British Heart Foundation. The authors and Bauman have no relevant financial relationships.
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