In the study, the researchers asked 73 mothers to give their babies skin-to-skin contact for one hour per day for two weeks. For comparison, the researchers also looked at 73 premature infants who only spent time in an incubator — the standard form of care for premature infants.

At age 10, the children who had received maternal contact as infants slept better, showed better hormonal response to stress, had a more mature functioning of their nervous system and displayed better thinking skills.

The results show that adding "maternal-infant contact in the neonatal period has a favorable impact on stress physiology and behavioral control across long developmental epochs in humans," Ruth Feldman, a professor of psychology at Bar-Ilan University in Israel, and her colleagues wrote in their study, published Jan. 1 in the journal Biological Psychiatry.

About 12 percent of infants in the United States and other industrialized societies are born prematurely, which is defined as at least three weeks before their due date. Rates of preterm birth are significantly higher in developing countries. Premature babies face a higher risk of lifelong problems such as intellectual disabilities, breathing problems, hearing loss and digestive problems, according to the Centers for Disease Control and Prevention.