09/15/2011 03:03 EDT | Updated 01/12/2012 02:08 EST

Moms 40-plus and their babies at highest risk for complications: report

TORONTO - Many older mothers have healthy birth experiences, but the risks associated with pregnancy and childbirth start increasing at age 35 and rise significantly for mothers age 40 and older, a study has found.

The report by the Canadian Institute for Health Information, entitled In Due Time: Why Maternal Age Matters, shows first-time mothers in their 40s are most at risk for delivery complications.

The findings are based on an analysis of more than one million hospital births from 2006-07 to 2008-09, the largest population-based study of its kind in Canada to measure the impact that advanced maternal age can have on both mothers and their babies.

"In Canada, almost one in every five births is to a mother over the age of 35, and this proportion is projected to continue to increase," Kathleen Morris, director of health system analysis and emerging issues at CIHI, said in a release Thursday.

Mothers age 40 and older are at least three times more likely to develop gestational diabetes and placenta previa than younger mothers, say the authors, who found that one in every eight mothers older than 40 developed gestational diabetes, compared with one in 12 aged 35 to 39 and one in 24 for those aged 20 to 34.

Gestational diabetes, a condition of elevated blood sugar that begins during pregnancy, can potentially cause high blood pressure in mothers and complications during delivery.

Placenta previa is a condition in which the placenta grows in the lowest part of the uterus and covers all or part of the opening to the cervix. It can lead to delivery complications and potential health risks for the child.

One in every 65 mothers age 40 or older experienced this condition, compared with one in 97 aged 35 to 39 and one in 208 ages 20 to 34, the study found.

"Good prenatal care can help manage the risks associated with gestational diabetes and placenta previa and ensure a healthy delivery," said Dr. Mark Walker, a senior scientist at the Ottawa Hospital Research Institute. "It is important to understand the relationship with age in order to properly manage the risk."

Other highlights of the study include:

-- Two of five mothers 40 and older -- and more than half of all first-time mothers in this age group -- had C-section deliveries, compared to about one in three mothers aged 35 to 39 and one in four aged 20 to 34.

-- Assisted vaginal deliveries, such as those requiring forceps or vacuum extraction, were also more common for older mothers with single births. About a third of first-time mothers in their 40s had an assisted delivery, compared with one-quarter of first-time mothers aged 20 to 34.

Babies born to older mothers are more likely to face adverse birth outcomes, such as a chromosomal disorder like Down syndrome. The three-year study found one in every 127 babies born to a mother 40-plus had a chromosomal disorder, compared with one in 370 infants born to mothers 35 to 39, and one in 1,000 whose mothers were 20 to 34.

The risk of having a preterm birth -- before the 37th week of pregnancy -- is also higher for older moms. Premature babies have not had the chance to develop fully in the womb and are more likely to face medical complications, ranging from difficulty breathing, vision problems and intestinal problems to neurological issues, such as cerebral palsy.