pregnancies of fertilization in vitro with frozen embryos appear to be linked to an increased risk of complications related to high blood pressure or hypertensive disorders, compared to when fresh embryos are used or when a pregnancy is conceived naturally.
This is what a study published on Monday (26) 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 complications in pregnancy related to high blood pressure was higher after implantation of frozen embryos compared with naturally conceived pregnancies, and the risk after using fresh embryos was similar to that of naturally conceived pregnancies, the data show.
More research is needed to determine whether similar findings would emerge in the United States or Brazil.
The researchers – from the Norwegian University of Science and Technology and other institutions in Europe – analyzed birth medical records from Denmark that were dated between 1994 and 2014, from Norway dated from 1984 to 2015 and from Sweden dated from 1985 to 2015. The records included about 4.4 million pregnancies conceived naturally, 78,300 pregnancies that used fresh embryos, and 18,037 pregnancies using frozen embryos.
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 using fresh embryos, and 4. 3% after natural conception. The data also showed that pregnancies from frozen and fresh embryos were more often premature – 6.6% of frozen and 8.1% of fresh, respectively – compared to those conceived naturally, at 5%.
“Frozen embryo transfers are now increasingly common across the world, and in recent years some clinicians have started skipping fresh embryo transfers to routinely freeze all embryos in their clinical practice, the so-called ‘freeze all’ approach. ,” said lead study author Sindre H. Petersen, a researcher at the Norwegian University of Science and Technology in Trondheim, Norway, in a press release on Monday.
“In summary, although most fertilization pregnancies in vitro are healthy and uncomplicated,” he said, “this analysis found that the risk of high blood pressure in pregnancy was substantially higher after frozen embryo transfer compared with pregnancies from fresh embryo transfer or natural conception.”
Petersen added: “Our results highlight that careful consideration of all potential benefits and risks is required before freezing all embryos as a routine in clinical practice.”
The findings are “in line with previous population-level studies” showing an increased risk of hypertensive disorders during pregnancy after frozen embryo transfer, the researchers wrote in their study.
Last year, a large study from France presented at the annual online meeting of the European Society for Human Reproduction and Embryology also found an increased risk of preeclampsia and hypertension in pregnancies derived from frozen and thawed embryos — and the risk was seen to be higher when the uterus was prepared for implantation with hormone replacement therapies.
“The association between frozen embryonic cycles and hypertensive disease in pregnancy has been known for some time, and there is still an active debate about the pros and cons of ‘freezing everything’ among fertility doctors,” said Ying Cheong, professor of reproductive medicine at University of Southampton, in a statement distributed by the UK-based Science Media Center in July. She was not involved in any of the studies.
“There are two important points to take home here, first, while frozen embryo transfer technology has transformed reproductive medicine, the technique should only be performed where it is clinically appropriate, and second, clinicians and scientists need to start connecting the dots. between what happens in early development and later at birth and beyond, an area of research, in my opinion, that is still under-supported and under-studied,” said Ying.
The new study didn’t look at what could be driving this association between frozen embryo transfers and high blood pressure risks, but some fertilization doctors in vitro question whether it is really a matter of freshness versus frozen.
“There’s one thing that’s not clear: is it from the embryo freezing procedure itself or is it from the protocol used?” asked reproductive endocrinologist Aimee Eyvazzadeh of San Francisco, who was not involved in the new study.
“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 medications to mimic ovulation.
“Studies show that it is the lack of a corpus luteum that increases the risk and this is potentially why a frozen transfer may have a higher risk of preeclampsia,” Aimee wrote in an email.
Overall, the new study is “very important” for “anyone caring for pregnant women after IVF,” she wrote. “Everyone who cares for pregnant women after fertilization in vitro should pay close attention to this study. More and more studies are showing what fertilization doctors in vitro already know that fertilization in vitro after transferring frozen embryos may increase the risk of preeclampsia.”
Source: CNN Brasil
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