"There is no question hypertension is increasing," he said. "Again, it is unclear exactly why. We know it is associated with older women, we know it is associated with first pregnancy and we know that there are more older women having first pregnancies."
But obesity, which is also associated with high blood pressure, is increasing and may be a reason as well, he said.
At the same time, the rate of lacerations from episiotomy decreased, the study found. This may have something to do with the increasing number of cesarean deliveries, Callaghan said.
The rate of cesarean delivery increased, from 21.8 percent from 1993 to 1997 to 28.3 percent from 2001 to 2005, the researchers reported. The reason for this increase is also unknown, Callaghan said.
"It may reflect an increase in the risk status of women who are getting pregnant, especially older women and women who are coming into pregnancy with chronic diseases," he said. "It also reflects changes in practice patterns and how physicians make decisions about when a cesarean is warranted."
Dr. Edmund F. Funai, chief of obstetrics at Yale University School of Medicine, said he thinks the authors were "spot-on in their conclusions."
"While studies derived from administrative data must be interpreted with caution, it is very true that more births are occurring in older women than ever before," Funai said. "One natural byproduct of aging is the likelihood of accruing chronic disease diagnoses, such as hypertension. Compounding this fact is the rise in the prevalence of obesity, which itself is associated with morbidities such as hypertension and diabetes. The effect of aging and obesity is also likely synergistic."
However, classifying cesarean delivery as morbidity does not seem to be seem relevant any longer, Funai said.
"Many patients and providers are more interested
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