Oct. 29 (UPI) -- Mothers who get pregnant less than 12 months after delivery had an increased risk for themselves and their baby, depending on the mom's age, according to a study in Canada.
Researchers at the University of British Columbia and the Harvard T.H. Chan School of Public Health in Boston found that the risks only applied to women older than 35, but all infants had an increased risk, and especially those of mothers between the ages of 20 and 34. The findings were published Monday in the JAMA Internal Medicine.
The researchers report that they found pregnancies spaced 12 to 18 months apart were the ideal length from a medical standpoint.
"The findings for older women are particularly important, as older women tend to more closely space their pregnancies and often do so intentionally," Dr. Laura Schummers, a postdoctoral fellow in the UBC Department of Family Practice who conducted the study as part of her dissertation at Harvard, said in a press release.
The study is the first first investigation of pregnancy spacing and maternal mortality or severe morbidity -- rare but life-threatening complications of pregnancy, labor and delivery in a high-income country.
Researchers examined 148,544 pregnancies from 2004 to 2014 in British Columbia from birth records, billing codes, hospitalization data, prescription data for infertility information and census records.
Among the pregnancies, 123,821 were women between ages 20 and 34 years, 7,184 were women younger than 20 years and 17,539 were women 35 years or older.
One-fifth of pregnancies among women 35 years or older were shorter than 12 months.
When the older women conceived six months after a previous birth, researchers found a 1.2 percent risk of maternal mortality or severe morbidity. Extending it to 18 months between pregnancies, the risk dropped to 0.5 percent.
The risk of spontaneous preterm labor for older women was about 6 percent at six months but 3.4 percent at the 1 1/2-year interval.
Among younger women, there was 8.5 percent risk of spontaneous preterm birth -- before 37 weeks of pregnancy after labor that started on its own -- for those spaced at six months. But it the pregnancies were spaced out 18 months, the risk dropped to 3.7 percent.
"Short pregnancy spacing might reflect unplanned pregnancies, particularly among young women," said Dr. Sonia Hernandez-Diaz, a professor of epidemiology at the Harvard T.H. Chan School of Public Health. "Whether the elevated risks are due to our bodies not having time to recover if we conceive soon after delivering or to factors associated with unplanned pregnancies, like inadequate prenatal care, the recommendation might be the same: improve access to postpartum contraception, or abstain from unprotected sexual intercourse with a male partner following a birth."
The findings are encouraging for older women planning their families.
"Older mothers for the first time have excellent evidence to guide the spacing of their children," said senior author Dr. Wendy Norman, an associate professor in the UBC department of family practice. "Achieving that optimal one-year interval should be doable for many women, and is clearly worthwhile to reduce complication risks."