Frozen embryos appear to be linked with a significantly higher risk of dangerously high blood pressure for the woman in pregnancies achieved through IVF, a major new study reports.

Expectant mums were 74% more likely to develop high blood pressure if her pregnancy resulted from a frozen embryo, as opposed to a fresh embryo or natural conception, according to analysis of more than 4.5 million pregnancies.

These results could mark a sea change in the way assisted reproduction is performed, researchers said.

“Frozen embryo transfers are now increasingly common all over the world, and in the last few years, some doctors have begun skipping fresh embryo transfer to routinely freeze all embryos in their clinical practice, the so-called ‘freeze-all’ approach,” said lead researcher Dr Sindre Petersen, a doctoral fellow at the Norwegian University of Science and Technology in Trondheim.