June 30 (UPI) -- Women who undergo in vitro fertilization using frozen-thawed embryos are at increased risk for experiencing sudden spikes in blood pressure, a study presented Wednesday during the European Society of Human Reproduction and Embryology annual meeting found.
Just over 5% of women who had IVF with frozen embryos and received hormone therapy before implantation developed rapid rises in blood pressure, a condition called pre-eclampsia, the data showed.
However, just over 2% of women experienced pre-eclampsia -- which can affect a variety of organs -- after IVF conducted during ovulation or using eggs and embryos that were never frozen.
Also, about 5% of women who underwent frozen-thawed IVF developed high blood pressure during pregnancy, compared with just over 3% of women who had the other procedures, according to the researchers.
Both pre-eclampsia and high blood pressure can lead to health complications for the mother and child.
"This study demonstrates that frozen embryo transfers [administered by] artificial cycle were significantly associated with an increased risk of vascular disorders compared to ovulatory cycle and fresh-embryo transfers," study co-author Dr. Sylvie Epelboin told UPI in an email.
"Among assisted reproductive techniques, frozen embryo transfers are increasing because, compared with IVF and fresh embryo transfers, they have the advantage of avoiding ovarian hyper-stimulation and further complications," said Epelbion, a gynecologist and obstetrician at Bichat-Claude Bernard Hospital in Paris.
More than 1 million babies in the United States have been born via IVF, and up to 40% of them from frozen embryos, research suggests.
IVF with frozen-thawed embryos is generally less expensive than other types of procedures because there is no egg retrieval and no anesthesia used, according to Epelboin and her colleagues.
The procedure also has been associated with lower risk for premature birth and low-birth-weight babies, as well as equal or higher success rates than those using fresh embryos.
Researchers said this is because frozen transfers appear to reduce the risk for ovarian hyperstimulation, a condition in which the ovaries become swollen and painful due to excess hormone exposure.
For this study, Epelboin and her colleagues analyzed data from the national IVF registry of France for nearly 70,000 pregnancies delivered after 22 weeks gestation between 2013 and 2018.
They divided the pregnancies from IVF and intracytoplasmic sperm injection into three groups: those derived from frozen embryo transfer in a natural "ovulatory" cycle, those from frozen embryo transfer with hormone replacement therapy and conventional "fresh transfers."
A higher risk of pre-eclampsia and high blood pressure existed in pregnancies derived from frozen-thawed embryos than in those produced using other methods, the data showed.
This risk was found significantly higher in those treatments in which the uterus was prepared for implantation with hormone replacement therapies.
The findings suggest that preparation of the uterus with hormones in an artificial cycle increases the risk for blood pressure disorders of pregnancy compared with procedures performed with preserved ovulation and fresh embryo transfers.
Based on the results, the researchers said that preservation of a woman's ovulatory cycle could be advocated as first-line preparation in frozen embryo transfers whenever possible.
"[Our] recommendation is to continue the policy of embryo freezing, which is beneficial in many respects, [but during] the ovulatory cycle, [either] natural or with a mild stimulation, rather than the artificial cycle," Epelboin said.
"The increase in vascular disorders of pregnancy is only found when the preparation for the embryo transfer is an artificial cycle, which involves prolonged treatment during the first stages of pregnancy with high doses of estrogen and progesterone," she said.