Pregnancies resulting from frozen embryo transfers are at greater risk of complications related to high blood pressure, according to new research.

High blood pressure (hypertension) in pregnancy can have serious consequences for both the mother and the fetus and complications such as pre-eclampsia. Dr Sindre Petersen from the Norwegian University of Science and Technology, Trondheim, Norway presented the findings at the annual meeting of the European Society of Human Reproduction and Embryology.

'This study was by far the largest sibling analysis to date investigating the association between assisted reproduction treatments and hypertensive disorders in pregnancy,' said Dr Petersen. 'Our findings are important because the number of [frozen embryo transfers] is rapidly increasing throughout the world.'

The study, by the Committee of Nordic Assisted Reproductive Technology and Safety, used data from more than 4.5 million pregnancies across three Nordic countries between 1988 and 2015. Pregnancies that resulted from frozen embryo transfers had almost double the chance of hypertensive disorders compared to those resulting from natural conception or fresh embryo transfers.

To exclude parental factors, the researchers were able to repeat the finding in a smaller group of 33,000 women who had two or more pregnancies – comparing pregnancies from frozen embryo transfers with those from fresh transfers or natural conception in the same woman. Researchers have not yet addressed the potential impact of maternal age, as a frozen embryo transfer would be likely to follow a fresh or natural embryo transfer at a later date.

Dr Peterson pointed out that the findings must be balanced against the fact that frozen embryo transfers facilitate transferring one embryo at a time, reducing the number of multiple pregnancies which are associated with greater risk for mothers and babies.

'I am confident that a well-grounded and individualised decision of whether to go for a fresh or a frozen cycle can be made after dialogue between the clinician and the couple, just as in all clinical decision making,' he said.

Professor Abha Maheshwari, clinical director of the Aberdeen Fertility Centre and lead clinician at Fertility Scotland told BioNews: 'Hypertensive disorders in pregnancy don't just affect outcomes for mother and baby in that pregnancy but have long-term implications for the mother. Hence, we as a community, have to do everything to minimise the risks.'

Sources and References

• 6 July 2022. 38th annual meeting of the European Society of Human Reproduction and Embryology
  Frozen embryo transfers in IVF linked to greater risk of maternal hypertension in pregnancy

Reproduced from BioNews with permission, a web- and email-based source of news, information and comment on assisted reproduction and human genetics, published by Progress Educational Trust.