Pregnancies resulting from in vitro fertilization using frozen embryos appear to have a higher risk of complications related to high blood pressure or blood pressure disorders, compared to when fresh embryos are used or when pregnancies are conceived naturally.

According to the study released on Monday American Heart Association Journal of Blood PressureIt includes data on more than 4.5 million pregnancies spanning three decades in three European countries: Denmark, Norway and Sweden.

Blood pressure-related pregnancy complications are higher after frozen embryo transfer compared to naturally conceived pregnancies, and the risk after fresh embryo conception is similar to naturally conceived pregnancies, the data show.

More research is needed to determine whether similar findings are found in the United States.

The researchers – from the Norwegian University of Science and Technology and other European institutions – analyzed medical birth records from Denmark between 1994 and 2014, from Norway from 1984 to 2015 and from Sweden from 1985 to 2015. The records are included. 4.4 million pregnancies conceived naturally, 78,300 using fresh embryo transfer and 18,037 pregnancies from frozen embryo transfer.

The researchers compared blood pressure disorders during pregnancy in the groups and found that 7.4% after frozen embryo transfer, 5.9% after fresh embryo transfer and 4.3% after natural conception were uncorrected for such diseases. The data showed that pregnancies with frozen and fresh embryo transfers were more likely to stillbirth – 6.6% frozen and 8.1% fresh, respectively – compared to naturally conceived pregnancies, 5%.

“Frozen embryo transfer is now becoming more common around the world, and in the past few years some doctors have begun to skip fresh embryo transfer in order to routinely freeze all embryos in their clinical practice. Lead study author Dr. Cindy H. Peterson, Ph.D. Fellow at the Norwegian University of Science and Technology in Trondheim, Norway; He said in a news release. Monday.

“In conclusion, although the majority of IVF pregnancies are healthy and uncomplicated, this analysis shows that hypertension during pregnancy is higher compared to frozen embryo transfer or natural conception,” he said.

Peterson added, “Our results show that careful consideration of all benefits and potential risks is needed before freezing all embryos as a routine in clinical practice.”

The findings “consistent with previous population-level studies” indicate an increased risk of hypertensive disorders after frozen embryo transfer during pregnancy, the researchers wrote in their study.

A large study out of France last year, presented online at the annual meeting of the European Society of Human Reproduction and Embryology, also found a higher risk of pre-eclampsia and high blood pressure in pregnancies from frozen embryos – and the risk was found to be even greater when the uterus is prepared for implantation with hormone replacement therapies.

“The link between frozen fetal cycles and gestational hypertension has been known for some time, and the current ‘freeze them all?’ Among fertility doctors, Dr Ying Cheng, professor of reproductive medicine at the University of Southampton A statement released by the Science Media Center in the UK In July. She did not participate in either study.

“There are two important take-home points here. First, while frozen embryo transfer technology will revolutionize reproductive medicine, FET should only be performed where it is clinically necessary. Second, clinicians and scientists must begin to bridge the gap between early development and what happens at birth and beyond. , in my opinion, is still an under-researched and under-studied area of ​​research,” Cheng said.

This new study didn’t evaluate what might be the link between frozen embryo transfer and high blood pressure risks, but some IVF doctors are questioning whether it’s really hot and frozen.

“There’s one thing that’s not clear: is it the freezing process or is it from the protocol? Most IVF doctors believe, based on recent studies and evidence, that it’s the drug protocol, not the IVF process,” said Dr. Amy Evazadeh, a San Francisco-based reproductive endocrinologist who was not involved in the new study. , wrote in an email sent to CNN. on Monday.

“There are different ways to prepare the uterus for transfer,” she said. A protocol a Corpus Lutum Cyst, the corpus luteum, a fluid-filled mass that forms in the ovaries and plays an important role during pregnancy, produces the hormone progesterone, which is important during pregnancy. Another protocol is based on drugs to induce ovulation.

“Studies show that it is the lack of corpus luteum that increases the risk, and as a result, frozen circulation may have a higher risk for pre-eclampsia,” writes Evazadeh.

Overall, the new study is important “for anyone caring for pregnant women after IVF,” she wrote. “Anyone caring for people who are pregnant after IVF should pay close attention to this study. More and more IVF doctors are becoming aware of the increased risk of pre-eclampsia after IVF frozen embryo transfer.”

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