A study in the Journal of the American Medical Association said intervals of 18-23 months between pregnancies posed the least health risks for babies.

In an analysis of 67 studies from 1966 to 2006 -- a third of which were conducted in the United States -- Colombian researchers determined that intervals shorter than 18 months and longer than 59 months increased the risk for three negative outcomes of delivery: low birth weight, preterm birth and small size for gestational age, The Washington Times reported.

Interpregnancy intervals shorter than six months were associated with a 1.4 times greater risk of premature birth; 1.6 times greater risk of low birth weight; and 1.26 times greater risk of SGA.

"Maternal nutritional depletion" is a "plausible explanation" for why short periods between pregnancies can mean harmful birthing outcomes, particularly in developing countries.

This hypothesis holds that a "close succession of pregnancies and periods of lactation worsen the mother's nutritional status" because there is not enough time for her to recover physiologically.

Copyright 2006 by United Press International