Using frozen embryos for IVF may raise the mother's risk of high blood pressure by 74 per cent, new research has suggested.
High blood pressure in pregnancy can lead to pre-eclampsia, a condition that affects about one in 25 births and can lead to complications for both mother and child.
Data from Scandinavia on 4.5 million pregnancies included information on the mother and baby of 18,000 pregnancies from IVF with frozen embryos and 78,000 from fresh embryos.
Analysis, published in the journal Hypertension, found that 7.4 per cent of mothers that had IVF with a frozen embryo suffered with hypertension, compared to 4.3 per cent for those that used a fresh embryo.
When adjusting for age, wealth and other confounders, the researchers found a frozen embryo transfer was linked to a 74 per cent increase in high blood pressure risk, compared with the rest of the population.
Dr Sindre Petersen, lead author of the study from the Norwegian University of Science and Technology, said: “In summary, although most IVF pregnancies are healthy and uncomplicated, this analysis found that the risk of high blood pressure in pregnancy was substantially higher after frozen embryo transfer compared to pregnancies from fresh embryo transfer or natural conception.”
A secondary form of analysis compared women who had several children, including one via frozen embryo IVF and one naturally, and found a frozen transfer was linked to a doubling in the risk of high blood pressure.
“Our sibling comparisons indicate that the higher risk is not caused by factors related to the parents, rather, however, that some IVF treatment factors may be involved,” added Dr Petersen.
“Future research should investigate which parts of the frozen embryo transfer process may impact risk of hypertension during pregnancy.”
Eggs are often frozen when a woman is younger to enable her to have children later in life but with the healthier and fitter eggs of her younger self. Official guidance in the UK was updated earlier this year so that they can now be stored for 55 years.
The technique is also used so women who are ill can have children before undergoing treatment, such as chemotherapy, which can damage their eggs.
The freezing, storing and thawing of eggs can cost up to £10,000, depending on the length of time they are kept on ice. The cost may be picked up by the NHS in the event of medical reasons.
Transfer also linked to higher cancer risk in child
“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 Dr Petersen.
“Our results highlight that careful consideration of all benefits and potential risks is needed before freezing all embryos as a routine in clinical practice.
“A comprehensive, individualised conversation between physicians and patients about the benefits and risks of a fresh vs frozen embryo transfer is key.”
A study on the same dataset but conducted by academics at the University of Gothenburg found frozen embryo transfer is also linked to a higher risk of cancer in the child.
The scientists of this study, published earlier this month, say the risk of cancer is 59 per cent greater for children born from a frozen embryo procedure than a fresh embryo, and 65 per cent greater than a natural conception.