Washington, DC -- The risk of ectopic pregnancy among women undergoing assisted reproductive technology (ART) is not as common as previously thought, according to a new study in the March issue of Obstetrics & Gynecology. The study found ectopic pregnancy risk to depend largely on the type of ART used to achieve pregnancy, the cause of infertility, and the number of embryos transferred.

The study also reports that ectopic pregnancy occurs in approximately 2% of ART pregnancies, on par with the ectopic rate for the general population and significantly lower than earlier estimates for women using ART methods (between 2.2% and 8.6%).

The study monitored 94,118 ART pregnancies between 1999 and 2001, of which 2.1% were ectopic. Researchers found that women who received zygote intrafallopian transfer (ZIFT) were nearly twice as likely to have an ectopic pregnancy as women using other ART methods. Additionally, ectopic risk was elevated in women with tubal factor infertility and in instances in which three or more embryos were transferred. Women with lowest risk of ectopic pregnancy included those who used donor eggs and those who carried ART pregnancies as surrogates.

High embryo implantation potential was found to be related to low ectopic occurrence when the number of embryos transferred was limited to one or two. Implantation potential was not directly measured, but was determined by examining how long embryos were kept in culture and whether some embryos were frozen for later use, two factors previously shown to be related to increased implantation and ART success rates. When embryos were assessed as having a high implantation potential and when only one to two embryos were transferred, ectopic rates were decreased; however, if three or more embryos were transferred, the implantation potential appeared to have no protective effect on the ectopic risk.

Factors such as maternal age and prior miscarriage were not found to influence ectopic occurrence.

Contact: Laura A. Schieve, PhD, National Center on Birth Defects and Developmental Disabilities, Centers for Disease Control and Prevention, Atlanta, GA, at lschieve@cdc.gov

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