March 12, 2007 -- Older moms are far more likely to have their babies delivered by cesarean section than younger moms, even when they have no obvious risk factors for a high-risk birth, new research shows.
The chance of delivering by C-section was greatest among older, first-time mothers. Half of first-time moms aged 45 and over had surgical births, as did roughly 40% of first-time moms aged 40 to 44.
Researchers reviewed 8 million U.S. single-child births occurring between 1995 and 2000 by examining birth certificate data.
After adjusting for known risk factors for surgical delivery, they found little difference in cesarean delivery rates among low-risk, first-time moms aged 35 and older and all women 35 and older who gave birth.
"It was really shocking that we didn’t see a difference between the low-risk women and all comers," researcher Barbara Luke, ScD, MPH, RN, tells WebMD.
The study was funded by the National Institute of Child Health and Human Development (NICHD).
In a statement, NICHD Director Duane Alexander, MD, calls for more research into why C-section rates are so high for older women.
"Until we learn why older mothers with low-risk pregnancies have a disproportionately high rate of cesarean delivery, the utmost caution is needed in evaluating older mothers as candidates for the procedure," he notes.
"Although older mothers share certain risk factors in common, each woman is a unique individual and the potential benefits and risks of cesarean delivery should be evaluated for her specific case."
More Older Moms
It is no surprise that more and more women are giving birth later in life. In just over two decades, first births increased threefold among women aged 30 and over, while they jumped sixfold in women 35 and older and 15-fold in women 40 and over.
It is also well known that older women tend to have more risk factors for cesarean delivery, and this was confirmed in the new study, published in the latest online issue of the journal Human Reproduction.
Using birth data from the National Center for Health Statistics, the researchers evaluated factors such as the mothers’ medical risk factors, pregnancy complications, and mode of delivery by age.
Compared to women under 35, older women were at much higher risk for complications during pregnancy and delivery. First-time mothers, regardless of age, were also more likely to deliver by C-section, even when their pregnancies were considered low risk.
Not surprisingly, women 45 and older were most likely to have high blood pressure and diabetes while pregnant, two big risk factors for C-section delivery. They were also at the greatest risk for experiencing excessive bleeding during labor and premature delivery.
But these and other known risk factors for problem births did not explain the excess of cesarean deliveries among older moms.
"This is a disturbing trend," Luke says. "C-sections are increasing, and women need to understand that there are risks involved. I am an old neonatal nurse, and I know the process of passing through the birth canal is beneficial for the baby. These babies tend to breathe better because they have less mucus."
Obesity and IVF
Luke says several factors that could not be measured in the study might explain the excess of surgical births in older mothers.
Obesity is a well-known risk factor for problem deliveries, and women tend to get heavier as they age.
Women 35 and older are also far more likely to undergo in vitro fertilization and other infertility procedures. Several studies suggest that infertility treatment increases the risk of pregnancy complications.
Other possible reasons for the age-related discrepancy include malpractice concerns among doctors and a preference for surgical delivery among older women.
NICHD project officer Rosalind B. King, PhD, tells WebMD that a better understanding of the trend is needed.
"It is clear that older mothers, particularly first-time mothers, have an increased risk for cesarean deliveries," she says. "It is also clear that we don’t fully understand this trend."