New York - The larger a pregnant woman is when she checks in on delivery day, the greater her risk of having a cesarean section, according to a US study.
Nearly one of every three births in the United States is now delivered by cesarean, a surgery that has been linked to complications for both mother and baby such as infection, bleeding and hysterectomy.
This rate is about 50 percent higher than it was in the mid-1990s, according to the US Centres for Disease Control and Prevention.
"As clinicians, we are faced with so many issues when taking care of patients with higher BMI (body mass index), and one of them is a greater risk for cesarean," researcher Dr. Michelle Kominiarek of Indiana University told Reuters Health.
She added while previous studies had already linked cesarean delivery and body mass index (BMI) - a measure of weight that takes into account height - none had been large or detailed enough to determine how other factors might alter that risk, such as prior births or cesarean sections.
So Kominiarek and her colleagues collected data on nearly 125 000 women from the National Institutes of Health's Consortium on Safe Labour who gave birth between 2002 and 2008.
They analysed the circumstances surrounding each birth, as well as the delivery route.
A total of 14 percent of the women underwent cesareans, report the researchers in the American Journal of Obstetrics and Gynaecology (http://link.reuters.com/fyc74n). They found that for every unit increase in BMI, as measured on arrival for delivery, a woman's risk of cesarean delivery rose by four percent.
The team also discovered that this risk varied depending on whether or not a woman had given birth before or had previously undergone a cesarean section.
A one-unit increase in BMI raised the risk of cesarean five percent for a woman delivering her first child, two percent for women with children and prior cesarean, and five percent for women with children but without a prior cesarean.
These effects remained after accounting for factors such as maternal age, race and cervical dilation at hospital admission.
Overall, those who had a prior cesarean had about double the risk of having another: more than 50 percent of labouring women with a BMI over 40, which is considered morbidly obese. Part of the motivation for repeat cesareans is concern over a vaginal birth tearing scars left over from the previous surgery.
Other factors associated with the risk of cesarean in the current study included an age of 35 or older, black or Hispanic race, and diabetes.
Exactly how obesity contributes to cesarean risk still has not been well addressed, added Kominiarek.
"What is ultimately the safest delivery route for someone with a high BMI? Is it best to have an elective c-section, or is it just as safe to labour and then have a c-section? It will require more research to answer such questions," she said. - Reuters