Frozen Embryo Use Now Linked to Pregnancy Complications From High Blood Pressure
New research has linked the use of frozen embryos in in vitro fertilization (IVF) with a higher risk of pregnancy complications linked to high blood pressure.
The massive study, which was published in the American Heart Association’s journal, Hypertension, analyzed data from more than 4.5 million pregnancies across nearly three decades in Denmark, Norway, and Sweden. The researchers found that the risk of pregnancy complications linked to high blood pressure like preeclampsia was greater after the transfer of frozen embryos vs. pregnancies that were conceived without reproductive assistance. The risk of pregnancy complications linked to the transfer of fresh embryos was similar to pregnancies that were conceived without reproductive assistance.
Here’s a specific breakdown of the risk of complications:
Frozen embryo transfer – 7.4%
Fresh embryo transfer – 5.9%
Pregnancy without reproductive assistance – 4.3%
The study’s researchers concluded that frozen embryo transfers are linked with a “substantially higher risk” of high blood pressure disorders in pregnancy. Conditions like preeclampsia can lead to complications like fetal growth complications, pre-term birth, or organ damage, per the Mayo Clinic.
“We thought that this research would be important because the number of pregnancies after frozen embryo transfer is increasing rapidly all over the world,” says lead study author Sindre H. Petersen, M.D., a Ph.D. fellow at the Norwegian University of Science and Technology.
Whether you recently went through IVF or are considering using the technology to conceive, you probably have some questions. Here’s what you need to know.
Why are frozen embryos linked to pregnancy complications from high blood pressure?
The study didn’t explore that—it simply found the link. But there may be something in the medication protocol that’s used in a frozen embryo transfer that could be behind this, says women’s health expert Jennifer Wider, M.D. “There are different ways to get the uterus ready for transfer, and the method used in frozen transfer may be the reason high blood pressure risk goes up,” she says.
The risk may also be due to age, says Jane Frederick, M.D., a reproductive endocrinologist and the medical director at HRC Fertility in Orange County, California. “Many patients who use IVF are older patients,” she says. Pregnancy complications linked to high blood pressure go up with age, with the National Institute of Child and Human Development (NICHD) noting that the risk of preeclampsia is higher in women over 40.
“Older women are the ones that are more prone to getting high blood pressure anyway, whether they got pregnant through an IVF cycle or not,” Dr. Frederick says. Many older patients are also having multiple births (i.e. twins) she says, and “multiple births are also linked to high blood pressure risk.”
But Dr. Petersen says age may not explain everything, given that his team also looked at siblings for the study. "It is possible that something else might be behind the higher risk after frozen embryo transfer," he says. “However, we believe our carefully designed sibling analysis should take these factors into account, the so-called confounding factors, including age.”
Why do people use frozen embryos?
In vitro fertilization (IVF) is a form of assisted reproductive technology, and it’s done in cycles, according to the American College of Obstetricians and Gynecologists (ACOG). With IVF, sperm from a partner or donor is matched with your egg or a donor egg to create an embryo in a lab. That embryo is either frozen for later use or implanted in your womb, with the hope of it creating a successful pregnancy, ACOG explains.
It’s common for people to freeze their embryos, says Dr. Frederick. She estimates that about 85% of the embryo transfers in her practice are frozen.
“We found that stimulating the uterus, allowing it to rest, and then transferring the embryo in a programmed cycle is much more successful,” she says. Using frozen embryos also allows for genetic testing, Dr. Frederick says. “It requires that we take a cell from the embryo, freeze the embryo, and run that cell for chromosomal analysis,” she says. “We use this a lot more for our older patients.”
Frozen embryos are also used when people want to have more than one child, provided they were able to create several embryos during an initial IVF cycle, Dr. Frederick says. “A lot of people come back for a second child and use their frozen embryos,” she says.
What precautions should you take?
Every medical procedure comes with risks, and Dr. Wider says it’s crucial to understand them in advance. “It’s important to discuss all the potential benefits and risks before figuring out if this is the best route for each patient,” she says.
It’s a good idea to know your risk of high blood pressure in advance of undergoing IVF, Dr. Frederick says.
Nicole Weinberg, M.D., cardiologist at Providence Saint John’s Health Center in Santa Monica, Calif., does evaluations of patients who are interested in becoming pregnant and recommends doing your best to have a healthy lifestyle. “You want to make sure that your blood pressure is well-controlled, and that you’re able to exercise without having an unusual heart rate,” she says. “Making sure that everything is healthy will lend itself to a more successful pregnancy.”
If you happen to have high blood pressure, talk to your doctor. “There are a lot of things we can do to offset high blood pressure,” Dr. Frederick says.
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