Spacing pregnancies between 18 to 23 months apart results in the lowest risks for the infant. Researchers call this spacing the "optimal interpregnancy interval," noting that it is associated with lower risks of low birth weight and premature delivery than either shorter or longer time periods between pregnancies. A study of 173,205 live births in Utah shows that infants conceived less than 6 months after the birth of a sibling have a 40% increased risk of low birth weight or premature birth. The study also shows that infants conceived more than 10 years after the previous sibling have double the risk of low birth weight and nearly double the risk of premature birth. An editorial notes that women who do not breastfeed may ovulate as soon as 27 days after delivery, whereas less than half of women who do breastfeed ovulate by 6 months after delivery. The actions of a woman have a profound influence on the interval between pregnancies.
The New England Journal of Medicine February 25, 1999;340:589-594, 643-644.
COMMENT: Another way to optimize healthy deliveries. Space your babies optimally. It is clear that having infants to close together will exhaust maternal nutritional reserves and lead to low weight infants but I am not certain as to the mechanism for greater than ten year observation.