Postmature Infants Not As Easily Calmed As Other Newborns

November 27, 1996

Psychologists are gaining new insights into the behavior of infants who remain in the uterus after they should have been born. The babies generally do not behave normally, although they usually are given no special attention.

An estimated 10 percent of babies are born with a condition known as Clifford's postmaturity syndrome, but little research has been done to investigate the possible social and emotional implications. Clifford's syndrome babies generally, though not always, are born sometime after 41 weeks of gestation. Because the environment in the uterus is no longer ideal to support the fetus, it begins living off of its own body fat.

Therefore, the babies are often born with an old-wizened appearance, compared to normal infants, and the skin is loose, dry and sometimes cracked and bleeding, due to dehydration. Psychologists are uncovering evidence that the extended gestation causes stresses that are manifested in difficulties associated with nursing.

Give a normal-term infant a minute amount of sugar dissolved in water, and it's like a sedative, almost immediately calming fitful, crying babies, and keeping them calm even after they no longer taste the solution. But if the same sugar solution is given to an infant born with Clifford's syndrome, the sweet taste has a less calming effect immediately, and there is no sustained calming after the taste is gone.

Barbara Smith, a research scientist in The Johns Hopkins University's Department of Psychology, discovered the diminished calming effect in postmature infants while studying how babies develop early attachments to their mothers.

A scientific paper about the findings will be published in the January issue of the Journal of Physiology and Behavior. The paper was written by Smith, Marie J. Hayes, a psychology professor at the University of Maine, and former graduate students Shawn M. Roberts of the University of Maine and Elizabeth Swanson of Hopkins.

In a previous paper, Smith and other researchers showed that normal-term infants stopped crying when given a solution containing 14 percent sucrose, or table sugar, and the postmature infants continued crying after receiving the mildly-sweet solution. In the current study, instead of monitoring the degree of crying, the psychologists observed movements, such as arm and leg movements.

Before receiving the sugar solution, both types of infants exhibited the usual movements, such as trembling of the lower lip, the arms, hands and legs and a nervous mouthing behavior. But the sugar solution did not calm such movements in the postmature babies.

The scientists studied the reactions of 31 new-born infants at Sinai Hospital in Baltimore. The infants were given only a 1-cc drop of sugar-solution at a time -- not enough to swallow but enough to taste. While the babies were videotaped, they received one drop of solution every 10 seconds for five minutes and were then observed.

After tasting the sugar solution, the postmature infants showed significantly more trembling than did the normal-term infants. For example, during the five-minute period in which they received the sugar solution, the postmature babies exhibited nearly three times as many tremors of the arms, legs or hands.

Ongoing research has led Smith and her colleagues to the surprising hypothesis that the sweet taste of sugar sedates infants by stimulating the same brain region affected by heroin, a circuit of neurons known as an opioid pathway. The postmature infants react much like infants born to heroin-addicted mothers, but the researchers emphasized that they do not yet have evidence linking the behavior of postmature and drug-addicted infants. They are, however, currently studying whether there is a connection. Perhaps the postmature and drug-addicted babies are tolerant to sugar because the opioid pathways in their brains already are being stimulated, Smith suggests. The drug-addicted babies have narcotics in their blood, and postmature infants might have a natural narcotic, opiate-like endorphins in their systems. Their brains may produce endorphins, the body's natural pain killers, to cope with the stresses associated with remaining too long in the uterus, Smith said.

Researchers are conducting follow-up studies to determine whether the postmature infants do, in fact, have elevated levels of endorphins in their blood.

Smith noted that not all babies born after 41 weeks are born with symptoms of Clifford's syndrome. "It's difficult to tell whether the fetus is suffering from postmaturity until it's born," she said.

Research has shown that 1-year-olds born with Clifford's syndrome exhibit a lower attention span than normal babies, are more restless and score lower on some tests. Another study showed that, at 4 to 5 years old, children who were postmature were more likely to experience social-interaction problems. However, more research is necessary to fully understand the long-term effects of the syndrome.

The psychologists noticed the difficulties of the postmature babies while studying how infants develop early attachments to their mothers. The mother's milk actually tastes sweeter than the 14-percent sugar solution, Smith said.

"Feeding them calms them," she said. "Then, mom becomes associated with that calming effect, and mom is calming."

The research was funded through grants from the National Institute of Child Health and Human Development and the March of Dimes Foundation.

Johns Hopkins University

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