Women who get pregnant using donated eggs are less likely to have blood pressure problems if the eggs come from a sister, Korean doctors have found.
By Michelle Roberts
BBC News health reporter in Copenhagen
Pregnancy-induced hypertension, which can be fatal, occurs more often in women needing donor eggs to conceive.
Researchers found using an unrelated donor's egg carried a 5.4 fold increased risk - but using a sibling egg raised the risk just 2.2 times.
The study was presented at a European fertility conference in Denmark.
Pregnancy-induced hypertension (PIH) is thought to occur in around 10% of pregnancies.
When it is more severe, and called pre-eclampsia, it can be very serious, killing between three and five women and 500 and 600 babies a year.
Dr SunHwa Cha and colleagues at Samsung Cheil Hospital in Seoul looked at the outcomes of 61 women who they helped to become pregnant in their clinic using donor eggs and IVF treatment.
They also looked at 127 women who had had IVF using their own eggs for comparison.
Early pregnancy loss occurred significantly more often among the women who used donor eggs to conceive - 34% versus 15% with typical IVF.
PIH occurred in 12.5% of the donor egg pregnancies compared to 3.7% of the standard IVF pregnancies.
When the researchers divided up the donor egg data they found unrelated eggs carried a much greater risk of PIH than eggs from a related donor.
Dr Cha said: "There are perhaps lessons here for family members.
"If they fully understand and accept the situation of the woman who cannot conceive due to premature ovarian failure, they may consider that donation from a sibling would improve the outcome both in terms of the wellbeing of the pregnant mother and the health of the baby."
Abnormal immune response
Based on their findings, they believe the immune system is likely to play an important role in PIH in these women.
Eggs donated by a sister are more likely to be genetically similar to the woman's own eggs than those from a stranger.
PIH is caused by a defect in the placenta, which joins mother and baby and supplies the baby with nutrients and oxygen from the mother's blood.
The researchers believe that the placenta formed after egg donation from a stranger may have more foreign elements and thus trigger abnormal responses from the mother, which could lead to PIH and pregnancy loss.
Currently, there is no way avoiding PIH other than delivering the baby.
However, if it is possible to anticipate who is at greatest risk, its effects could be minimised by early diagnosis and management.
Michael Rich, of the charity Action on Pre-eclampsia, said: "This welcome research will give women the knowledge that they need to make increasingly complex decisions.
"However, it is also important that women bear in mind the other risk factors that may be affecting them at the same time."
The risk of pre-eclampsia is higher for women over 40, those who are obese, and those who have a family history of the disorder.