Pregnancies resulting from in vitro fertilization using frozen embryos appear to be linked to an increased risk of complications related to high blood pressure or hypertensive disorders, compared to the use of fresh embryos or the natural conception of pregnancy.
That’s according to a study published Monday in the American Heart Association’s journal Hypertension, which included data on more than 4.5 million pregnancies, spanning nearly three decades, in three European countries: Denmark, Norway and Sweden.
The risk of pregnancy complications related to high blood pressure was higher after frozen embryo transfer compared to naturally conceived pregnancies, and the risk after fresh embryo transfer was similar to that of naturally conceived pregnancies, according to the data.
Further research is needed to determine if similar results would emerge in the United States.
The researchers – from the Norwegian University of Science and Technology and other institutions in Europe – analyzed medical birth records from Denmark dated between 1994 and 2014, from Norway dated from 1984 to 2015 and from Sweden dated from 1985 to 2015 The registries included approximately 4.4 million naturally conceived pregnancies, 78,300 fresh embryo transfer pregnancies, and 18,037 frozen embryo transfer pregnancies.
The researchers compared the odds of hypertensive disorders during pregnancy between the groups and found that the unadjusted risk of such disorders was 7.4% after frozen embryo transfer, 5.9% after frozen embryo transfer. fresh embryo and 4.3% after natural conception. The data also showed that pregnancies resulting from frozen and fresh embryo transfer were more frequently preterm – 6.6% frozen and 8.1% fresh, respectively – compared to naturally conceived pregnancies, at 5%.
“Frozen embryo transfers are now becoming more common around the world, and in recent years some physicians have begun to skip fresh embryo transfer to routinely freeze all embryos in their clinical practice, l so-called ‘freeze everything’ approach,” the study’s lead author, Ph.D. Dr. Sindre H. Petersen. researcher at the Norwegian University of Science and Technology in Trondheim, Norway, said in a press release Monday.
“In summary, although most IVF pregnancies are healthy and uncomplicated,” he said, “this analysis revealed that the risk of high blood pressure during pregnancy was significantly higher after embryo transfer frozen versus pregnancies resulting from fresh embryo transfer or natural conception”.
Petersen added, “Our results emphasize that careful consideration of all potential benefits and risks is necessary before freezing all embryos as a routine in clinical practice.
The results are “consistent with previous population-level studies” showing a higher risk of hypertensive disorders in pregnancy after frozen embryo transfer, the researchers wrote in their study.
Last year, a large study out of France presented at the online annual meeting of the European Society of Human Reproduction and Embryology also found a higher risk of pre-eclampsia and hypertension in pregnancy-derived pregnancies. frozen-thawed embryos – and the risk was found to be greater when the uterus was prepared for implantation with hormone replacement therapy.
“The association between frozen embryo cycles and hypertensive disease in pregnancy has been known for some time, and currently there is still an active debate surrounding the pros and cons of ‘Freeze all for all?’ among fertility doctors,” said Dr Ying Cheong, professor of reproductive medicine at the University of Southampton, in a statement distributed by the UK-based Science Media Center in July. of the two studies.
“There are two important takeaways here, firstly, as frozen embryo transfer technology has transformed reproductive medicine, FET should only be performed where clinically appropriate and secondly, clinicians and scientists need to start making the connection between what happens in early development and later at birth and beyond, an area of research, in my view, that is still poorly supported and poorly studied,” said Cheong.
The new study didn’t assess what might be behind this association between frozen embryo transfers and high blood pressure risk, but some IVF doctors question whether it’s really fresh or frozen.
“There is one thing that is not clear: does it come from the actual procedure of freezing the embryo or does it come from the protocol used? Most IVF doctors believe, based on recent studies and evidence, that it is actually the medication protocol, not the IVF procedure,” wrote Dr. Aimee Eyvazzadeh, endocrinologist at the San Francisco-based reproduction, which was not involved in the new study, in an email to CNN. In Monday.
“There are different ways to prepare a uterus for transfer,” she said. One protocol involves a corpus luteum cyst, a fluid-filled mass that forms in the ovaries and plays an important role during pregnancy, as the corpus luteum produces the hormone progesterone needed during pregnancy. Another protocol relies on drugs to mimic ovulation.
“Studies show that it is the absence of the corpus luteum that increases the risk and this is potentially why a frozen transfer may have a higher risk of pre-eclampsia,” Eyvazzadeh wrote.
Overall, the new study is “very important” for “anyone caring for pregnant women after IVF,” she wrote. “Anyone caring for pregnant women after IVF should pay particular attention to this study. More and more studies are showing what IVF doctors already know, namely that IVF after embryo transfer frozen can increase the risk of pre-eclampsia.”
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