It's one of the first questions a pregnant mother (who wants multiple children) will ask her doctor before giving birth: How long do I have to wait before having another child?
Despite conflicting information that has ranged anywhere from six to 18 months, new research from the University of British Columbia (UBC) and the Harvard T.H. Chan School of Public Health says 12 months may be a sufficient amount of time to wait before safely conceiving again.
According to the study, published in the JAMA's Internal Medicine journal , the risk of serious health issues—affecting both mom and baby—was higher for women who got pregnant six months after previously giving birth, compared with those who waited for at least 12 months to 18 months.
To narrow down the best (and safest) time for a woman to conceive after giving birth, analysts combed through the results of 148,544 documented pregnancy records in British Columbia between 2004 and 2014. While searching, they also looked at women’s ages to see if those 35 and older might be at a higher risk.
Serious health issues—affecting both mom and baby—was higher for women who got pregnant six months after previously giving birth.
What they discovered was that 85 out of 1,000 women—between the age of 20 and 34 years old—who conceived six months after their last baby was born, had premature births. The risk was significantly lower (37 cases per 1,000) for those who waited at least 18 months.
"The very lowest risk time that we found was 18 months," said Laura Schummers, lead author and a postdoctoral fellow at UBC's department of family practice. "But what we found also was that risks between 12 and 24 months were basically equivalent to those at 18 months."
Schummers added that women 35 and older often plan to have closely spaced pregnancies. "Among younger women, the pregnancy is less often planned if it's closely spaced," she said. "If someone has a baby and six months later, they discover they are pregnant, perhaps that's not intended. We thought because older women more often plan to have their pregnancies closer together, they might not have the increased risks that are due to unintended pregnancies."
Though researchers believe these findings may offer “new, robust evidence to guide clinicians counseling women considering short interpregnancy intervals" and help reassure older women "who must weigh the competing risks of increasing maternal age with longer interpregnancy intervals," Schummers said that women’s decisions regarding optimal timing and spacing of pregnancy are “multifactorial." Also, "modest increases in risk associated with short intervals may not outweigh other factors, including those unrelated to health outcomes, that women and families consider in spacing their pregnancies."