Women who smoke during pregnancy are at risk for having a child with colic, according to a review of previous studies. Although the reason for the association is unclear, it may involve increased levels of an intestinal hormone called motilin.

As reported in the medical journal Pediatrics, Dr. Edmond D. Shenassa, from Brown Medical School in Providence, Rhode Island, and Dr. Mary-Jean Brown, from Harvard School of Public Health in Boston, reviewed the findings of six studies that looked at the link between maternal smoking and excessive crying or colic in infants.

The investigators found that only one of the studies used Wessel’s “rule of threes” to define colic: crying for at least 3 hours per day, at least 3 days per week, for at least 3 weeks. The other studies used less stringent criteria.

Findings from five of the studies support an association between maternal smoking and colic, as well as excessive crying, the researchers note. Further support comes from recent studies of the intestinal tract that have linked smoking with elevated motilin levels and higher-than-average motilin levels with an increased risk of colic.

Still, the authors note, the chain of events from maternal smoking to the development of colic has not been documented in a single study. To do this, a forward-looking study starting during pregnancy is needed, they add.

“In the US, nearly one half of all women smokers continue to smoke during their pregnancies,” the investigators point out. “If, as we suspect, exposure to cigarette smoke increases the risk of colic, then this would provide additional incentive to parents to abstain from smoking.”

SOURCE: Pediatrics, October 2004.