Women who use donated eggs to get pregnant by in vitro fertilization (IVF) might be more at risk for a common but potentially dangerous pregnancy complication than women using traditional IVF, a small study suggests.

Women who get pregnant using IVF - in which an egg is fertilized outside the body, then implanted into a woman’s uterus - are already thought to be at an increased risk for preeclampsia. The condition occurs when a woman’s blood pressure rises during her second or third trimester and her kidneys stop being able to retain protein.

Now it looks like using a donated egg could possibly increase that risk further - but more studies are needed to confirm the finding, doctors say.

“The results of this study should not be alarming or frightening,” said Dr. Peter Klatsky, the lead author of the paper from Women and Infants Hospital in Providence, Rhode Island. Rather, he said, the finding may help doctors understand what causes preeclampsia and how to counsel patients who may be at risk.

Though relatively common, preeclampsia is not well explained. Pregnant women develop the condition in about one in twenty pregnancies, and the only cure is giving birth.

For women who have carried a baby full term - at least 37 weeks - doctors may induce labor. In those who are earlier in their pregnancy, doctors closely monitor symptoms to make sure they don’t get worse.

Previous studies have shown that women who use donor sperm and those who get pregnant with a new sexual partner have higher rates of preeclampsia than other women. That suggested that the condition could be related to the body’s immune response to cells it doesn’t recognize. So Klatsky and his colleagues wanted to test if that pattern held true for eggs that the body would consider “foreign.”

They compared 77 women who had given birth using donated eggs between 1998 and 2005 with 81 similar women who had gotten pregnant using IVF with their own eggs. The researchers noted how many women in each group were diagnosed with either preeclampsia or pregnancy-related high blood pressure during their third trimesters, as well as how many gave birth to their babies prematurely.

The results, published in Obstetrics & Gynecology, show that about five percent of women who used their own eggs for IVF developed preeclampsia, compared to almost 17 percent of women using donor eggs. Women using donor eggs were also more likely to get high blood pressure without kidney problems and to deliver early.

The findings also showed that women who got pregnant using embryos that had been frozen and then thawed were more at risk for preeclampsia than women using fresh embryos. While the researchers did not initially set out to test that, Klatsky said it’s a possible effect that’s worth looking into with future studies.

He also said the findings suggest that doctors may want to keep a close eye on patients who got pregnant using donor eggs to make sure they don’t start developing signs of preeclampsia.

Dr. Sacha Krieg, an obstetrician who studies infertility at the Kansas University Medical Center and was not involved with the study, agreed that doctors should counsel patients at increased risk for preeclampsia and monitor them more closely during pregnancy.

But she cautioned against trying to draw too much of a conclusion from a small study. Rather than looking backwards at records of women who have already given birth, she hopes that future studies will start with women who are just getting pregnant and track their health as they go through their pregnancy. While harder to conduct, such studies can often give researchers more accurate information.

What both Klatsky and Krieg do hope is that this study will give researchers more clues about how preeclampsia develops. Having more information about the condition could help doctors “develop better treatments and better ways to prevent it, and better ways to counsel patients about their risks,” Klatsky said.

Signs continue to point to preeclampsia having something to do with the body’s immune response when it recognizes foreign cells. That would make sense, Krieg said. “We know that the immune response is important for both implantation and development of the fetus,” she said. Doctors need to learn more about how a fetus implants in the uterus, Krieg added, because this is probably where the early stages of preeclampsia start, even if women don’t show symptoms until much later.

The main message of the study, Klatsky said, is not that women who have gotten pregnant using donor eggs should be scared of developing preeclampsia. It’s that doctors should be aware of possible risks to their patients, and most importantly that researchers should keep tracking the immune system response in pregnant women.

“This is exciting because it sheds new light on to a potential cause of this common disease,” he said.

SOURCE: Obstetrics & Gynecology, December 2010.