The hormone oxytocin is related to familial bonding in animals and is tied to love and friendship in humans. Species that have more of it tend to develop stronger bonds.

Oxytocin is considered a key hormone for monogamy in the animal kingdom. One study of humans found that just sniffing a little oxytocin made people more trusting of others.

Now scientists find that mothers with high levels of oxytocin during pregnancy bond better with their babies.

More interaction

Researchers measured oxytocin levels in 62 pregnant women during the first trimester, third trimester and first month after delivery. Then they observed the mother and infant interact, defining levels of attachment based on gaze, touch, the use of "motherese" speech and other factors, including surveys filled out by the new mothers.

Mothers with a high level of the hormone in the first trimester engaged in more of the bonding behaviors after birth, the scientists found. Also, moms with lots of the hormone during the entire pregnancy and in the first postpartum month were more likely to sing special songs to infants and otherwise treat them special. They also worried more, checking on the infants more often than other mothers.

The study, led by psychologist Ruth Feldman at Bar-Ilan University in Israel, is detailed in the November issue of the journal Psychological Science.

"When mothers touch or hold their infants frequently, oxytocin is increased, and when mothers are prevented from touching, it decreases," Feldman told LiveScience. "We think that this is part of the reason why mothers and premature infants have difficulty bonding. It is highly recommended that mothers engage in some form of touch after premature birth, such as kangaroo care or massage."

How it works

There are several theories about how oxytocin affects social affiliation, Feldman said. It might simply reduce anxiety. Or it might in some unknown way increase behavior that promotes attachment.

The hormone has been tied to sexual bonding in humans as well as intimate friendships, too, Feldman said. And in previous work, Feldman and others have shown that oxytocin levels tend to be low in mothers suffering postpartum depression.

The new study was funded by the Israel Science Foundation, the U.S.-Israel Bi-National Science Foundation and a grant from the Brain Sciences Center at Bar-Ilan University.