In the most comprehensive look yet at the safety of abortion, researchers at UC San Francisco have concluded that major complications are rare, occurring less than a quarter of a percent of the time, about the same frequency as colonoscopies.

The study, published online in Obstetrics & Gynecology, analyzed data from more than 50,000 women enrolled in the Medi-Cal fee-for-service program who obtained abortions from 2009 to 2010, and looked for complications that occurred within six weeks of the procedure.

The rate is similar to what has been found in previous studies, but this is the first study in which researchers have based their conclusions on complete data on all of the health care used by women who have received abortions. Since some women must often travel long distances to find abortion providers, they tend to receive follow-up care at facilities closer to where they live. For many women, this means their local emergency department. But, up until now, no study has systematically examined emergency department use for post-abortion care.

The researchers said they expect the study will contribute to the national debate over abortion safety. Many state legislatures have recently passed laws that have the effect of reducing access to abortion by requiring providers to have transfer agreements or admitting privileges with hospitals or to construct their clinics so that they meet the requirements of an ambulatory surgical center. But the researchers said that these restrictions were likely to make women travel further to get abortions or induce them on their own using unsafe methods, both of which may increase the risks for women.

"Our study had very complete follow-up data on all of the women in it, and we still found a very low complication rate," said Ushma Upadhyay, PhD, MPH, an assistant professor at Advancing New Standards in Reproductive Health (ANSIRH), a program of the Department of Obstetrics, Gynecology and Reproductive Sciences at UCSF. "Abortion is very safe as currently performed, which calls into question the need for additional regulations that purportedly aim to improve safety."

California is one of 17 states that cover abortion and follow-up care for women enrolled in Medicaid, the state-federal health insurance program for the poor. Billing data from the Medi-Cal fee-for-service program gave researchers a complete picture of all the health care that women received in the six weeks following their abortion procedures.

California has more than 500 abortion providers, most of them practicing in an outpatient setting, and 97 percent of the abortions studied were performed in an outpatient clinic or a doctor's office. Only 3 percent were performed in hospitals.

Of the 54,911 abortions studied, just 126 cases involved major complications, which the researchers defined as conditions that required hospital admission, surgery or a blood transfusion. In all, a little less than two percent of the abortions, or 1,030 cases, resulted in minor complications in the six weeks following the procedure.

Women in their 30's were somewhat more likely than those in their early 20's to experience complications. Medication abortions also had a higher rate of complications compared to aspiration or surgical abortion. This was mostly due to needing an aspiration after a medication abortion, a well known, but not serious, risk of the method.

Researchers said the complication rate may be somewhat overstated in comparison to the total group of women seeking abortions around the country, since the women in the study were all low income. A wealthier population with private insurance may be healthier and less inclined to have abortion-related complications.