BOSTON -- In Tuesday's medical news, NewsCenter 5's Liz Brunner reported on new information for women considering having more than one child, keeping the blood flowing on your next flight, and news about dental fillings that contain mercury.

Childbearing Choices

Women who get pregnant within six to 17 months of giving birth are at higher risk of delivering prematurely, according to new research.

According to the Journal of the American Medical Association study, women who got pregnant in that time frame were 40 percent more likely to deliver prematurely. The risk of having a low-birth weigh baby was 61 percent greater. Mothers were also 26 percent more likely to deliver a small child if they had their children close together.

Similar risks were found for women who waited five years or more between pregnancies. Researchers found the safest spacing between pregnancies may be 18 to 23 months.

Researchers noted that as more women wait until they're older to start families, they may not want to wait 18 months or two years before getting pregnant again.

Blood Clots

Next time you take a long flight, you might want to consider wearing compression stockings, according to new research.

British researchers tracked nearly 3,000 passengers during flights lasting more than seven hours and found that passengers who wore the special stockings had a 10 percent lower risk of developing traveler's thrombosis, or blood clots.

The passengers also reported much less discomfort and swelling when they got to their destination.

Dental Dilemma

There is little reason to be concerned if your child needs fillings on their next trip to the dentist, according to two new studies.

Both studies compared the effects of amalgam fillings, which contain mercury, and resin fillings, which do not. After five to seven years, researchers found no differences in IQ, memory tests, kidney function, asthma or neurological conditions, including autism, between the two groups.

Children with mercury fillings did have more mercury in their urine, but overall, researchers at Boston's Children's Hospital and in Portugal said the studies should be reassuring to parents.