Baby massage is as beneficial to premature infants as it is adorable—a new study finds that massage therapy can markedly reduce stress in male preemie babies, though the effect is not as great for females.

Preemie, or premature, babies are born at least three weeks before a full 40-week pregnancy term. Because they do not have enough time to develop in the womb, preemie babies often have immature nervous systems that cannot adjust to the most minor stressors.

While newborn intensive care units (NICUs) in hospitals help keep the preemies alive, the whirring machinery, constant monitoring, and separation from their mothers only add to the stressed-out babies' anxieties.

A new study published last month in the journal Early Human Development finds that massage therapy actually promotes the maturing of preemies' immature autonomic nervous systems (ANS), reducing the babies' stress and putting them at ease.

Testing the Effects of Massage on Premature Babies

Researchers at the University of Utah, led by Dr. Sandra Smith of the University of Louisville School of Nursing, tested the benefits of a massage therapy on 17 premature infants against a control group of 20 babies that were not massaged.

Twice a day for four weeks, licensed massage therapists gently rubbed the babies for 20 minutes, using techniques modeled on Infant Massage USA. The baby massage involved six main compression strokes: thighs to feet, chest to ribcage, shoulders to hands, head from crown to neck, and along the back of the neck to the waist. The massage was followed by light movements of the arms and legs.

Before, during, and after the massage therapy, researchers collected data on the babies' heart-rate variability (HRV), an observable measure of autonomic nervous system function, using electrocardiograms (ECG).

Preemie babies usually have lower HRV than normal term babies, and the researchers write that the measure is significantly linked to increased stress response and likelihood of sleeping prone, which is associated with sudden infant death syndrome (SIDS).

Infant Massage Reduces Stress in Baby Boys, But Not Girls

Data analysis revealed that baby massage therapy increased HRV in male preemies, but not in females.

In massaged male babies, HRV increased every week they received the therapy—suggesting that infant massage promoted ANS maturation and presumably made them more resistant to stress. However, there was no effect on female babies who were massaged.

"We were surprised to learn the differences in the impact of massage therapy on preterm boys and girls," Smith said in a news release.

She suspected that hormonal factors could explain the discrepancy, though the current research offers no explanation.

Still, the benefits of controlled baby massage for male infants are still significant. Previous research found that male preemie babies have a higher mortality rate than females, and also may be more vulnerable to low blood pressure and stress-related metabolic and immune problems. Promoting ANS development with massage could help counteract those risks.

It's unclear exactly how baby massage might advance nervous system development, though Smith expects that future studies on its mechanisms and long-term effects on preemies will help explain.

Check out this video from for tips on how to massage a premature baby: