The drugs -- called mycophenolic acid products -- reduce the risk of organ rejection by suppressing the immune system. The study included 163 female transplant patients who discontinued mycophenolic acid products prior to conception and 114 who conceived while taking the anti-rejection drugs.
Those who stopped taking mycophenolic acid products before they became pregnant had more live births (79 percent vs. 43 percent), fewer miscarriages (19 percent vs. 52 percent) and a lower rate of birth defects (6 percent vs. 14 percent) than those who were taking the drugs when they conceived.
Women who stopped the anti-rejection drugs before they became pregnant did not have an increased risk of kidney problems, according to the study, which is scheduled for presentation in early November at an American Society of Nephrology meeting in Atlanta.
Although the study found an association between the drugs and increased pregnancy and birth risks, it did not prove a cause-and-effect relationship. The data and conclusions also should be viewed as preliminary until published in a peer-reviewed journal.
"The results of this study generate multiple questions. Continued close collaboration among specialists will help to better identify potential pregnancy risks in kidney transplant recipients, particularly as new immunosuppressive [drugs] are developed," study author Dr. Serban Constantinescu, of the Temple University School of Medicine, said in an American Society of Nephrology news release.
"Individual physicians and transplant centers are encouraged to report all pregnancy exposures in transplant recipients to the National Transplantation Pregnancy Registry, which was designed specifically to assess the safety of pregnancy in solid organ transplant recipients," Constantinescu said.
The National Kidney Foundation has more about pregnancy and kidney disease.