It has long been recognized that having offspring with short intervals between pregnancies is associated with a high risk of having a damaged child. An unanswered question has been “what is the ideal interpregnancy interval?”

Early this year, researchers based in Utah reported on their attempt to answer that concern by examining records related to the 300,000 singleton infants born in Utah between 1989 and 1996.

This team of researchers concluded that “infants … conceived 18 to 23 months after a previous birth have the best chance of being born healthy and this is considered to be the ideal interval for a mother”.

Seeking to learn more about the “natural” interval between pregnancies in humans, the research workers had separated out and analyzed data regarding possible risk conditions, such as the mother’s age at delivery, her nourishment status, tobacco and alcohol use, the number of years of her education, and a dozen other reproductive risk factors.

The researchers were comparing these factors against the frequency that three adverse outcomes occurred in the newborns – low birth weight, premature delivery, and small size for gestational age.

Each adverse outcome showed a pattern of both shorter and longer interpregnancy intervals being associated with higher risks.

(Effect of the Interval Between Pregnancies on Perinatal Outcomes, Bao-Ping Zhu et al; New England Journal of Medicine, February 25, 1999)