Women have yet another reason to stop smoking while pregnant. In the largest study of its kind, plastic surgeons say they found smoking during pregnancy significantly elevates the risk of having a child with excess, webbed or missing fingers and toes.

In fact, the study, published in the January issue of Plastic and Reconstructive Surgery, found that smoking just half a pack per day increases the risk of having a child born with a toe or finger defect by 29 percent.

"Reconstructive surgery to repair limb, toe and finger abnormalities in children represents a large portion of my practice - it is the most common issue I treat," said Benjamin Chang, MD, ASPS member and study author.

"Parents would ask why this happened to their child, but I didn't have an answer. This study shows that even minimal smoking during pregnancy can significantly increase the risk of having a child with various toe and finger defects."

Researchers examined the records of more than 6.8 million live births in the United States during 2001 and 2002, finding 5,171 children born with a digital anomaly where the mother smoked during pregnancy but did not suffer from other medical complications, such as heart disease, diabetes or high blood pressure.

The study authors discovered pregnant women who smoked one to 10 cigarettes per day increased the risk of having a child with a toe or finger deformity by 29 percent. The more a woman smoked, the higher the risk became. Women who smoked 11 to 20 cigarettes a day raised the risk 38 percent, and women who smoked 21 or more cigarettes per day raised the risk 78 percent.

Known as polydactyly, syndactyly and adactyly, these deformities are the most common congenital limb abnormalities. Polydactyly is the presence of more than five digits on the hands or feet. Syndactyly is having fused or webbed fingers or toes. Adactyly is the absence of fingers or toes.

Webbed fingers or toes occur one in every 2,000 to 2,500 live births and excess fingers or toes occur one in every 600 live births. Webbed fingers or toes occur twice as often in boys and are more common in Caucasians than African Americans. Excess digits, however, are 10 times more common in African Americans and are only slightly prevalent in boys.

The majority of these defects occur without any family history and most causes are unknown which has lead researchers to investigate environmental causes, such as smoking, for these anomalies.

"The results of this study were interesting. We suspected that smoking was a cause of digital anomalies but didn't expect the results to be so dramatic," Chang said.

"Smoking is so addictive that pregnant women often can't stop the habit, no matter what the consequences. Our hope is this study will show expectant mothers another danger of lighting up."