Women who put on a small amount of weight between pregnancies and add on enough pounds while pregnant are less likely to give birth to dangerously tiny babies, according to a report released Friday.

The investigators found that women who gained weight between pregnancies were 20 percent less likely to give birth to a baby that was small for his or her gestational age-meaning, the baby fell below the tenth percentile for birth weight.

Women who only gained a little weight during pregnancy - defined as less than half a pound per week - were also 90 percent more likely to give birth to an extremely small baby, the authors note in the journal Obstetrics & Gynecology. -

These findings suggest that while gaining weight between pregnancies may help your baby, making sure you gain enough while pregnant may be more important, the authors write.

Furthermore, they caution that exactly how much weight women should gain is not clear, and gaining too much can be unhealthy for both mother and child. “Gaining excessive weight can lead to production of a large birth weight infant, especially among obese women, which has its own risks,” they write.

This is not the first study of this subject, with previous research showing that underweight moms-to-be have an up to two-fold higher risk of delivering babies that are small for their gestational age.

To investigate whether weight gain between pregnancies also influenced babies’ health, Dr. Christine J. Cheng at Washington University School of Medicine in St. Louis, Missouri and her colleagues reviewed the birth certificates of more than 8,000 babies born small for their gestational age, and compared them to the same number of normal weight babies.

They found that, for a woman of average height and weight - around 5 feet and 5 inches, about 140 pounds - gaining 4-1/2 pounds between pregnancies reduces their risk of having a baby that is small for its gestational age by 16 percent.

Mothers were also less likely to deliver small babies if they gained enough weight during pregnancy, were free of heart disease, had never given birth to an overly tiny baby, didn’t smoke and did not experience high blood pressure related to pregnancy, known as preeclampsia.

Babies that are small for their gestational age are known to have a higher risk dying during their first days of life and a higher risk of a number of later problems, such as poor physical growth, and trouble in school.

SOURCE: Obstetrics & Gynecology, August 2004.