Frozen embryo transfer confers risk for hypertensive disorders of pregnancy
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Risk for a hypertensive disorder of pregnancy after a frozen embryo transfer was substantially higher than after natural conception, even when controlling for constant parental characteristics within sibships, researchers reported.
In a population-based analysis of data from three countries spanning 30 years, researchers also found that pregnancies after a fresh embryo transfer were at a similar or lower risk for hypertensive disorder of pregnancy compared with naturally conceived pregnancies. Hypertensive disorders of pregnancy are the second leading cause of maternal death behind maternal hemorrhage and are a significant cause of short- and long-term maternal and offspring morbidity worldwide.
“Frozen embryo transfers are now increasingly common all over the world, and in the last few years, some doctors have begun skipping fresh embryo transfer to routinely freeze all embryos in their clinical practice, the so-called ‘freeze-all’ approach,” Sindre H. Petersen, MD, a doctoral fellow at the Norwegian University of Science and Technology in Trondheim, Norway, said in a press release.
Petersen and colleagues analyzed data from 4,426,691 naturally conceived pregnancies, 78,300 fresh embryo transfers and 18,037 frozen embryo transfer singleton pregnancies, of which 33,209 sibships were conceived using different conception methods. Researchers used the Medical Birth Registries of Denmark (1994-2014), Norway (1984-2015) and Sweden (1988-2015), linked to data from national quality registries and databases on assisted reproduction.
Researchers estimated adjusted ORs for hypertensive disorders of pregnancy for fresh embryo transfer and frozen embryo transfer vs. natural conception; random-effects models provided conventional population-level estimates and fixed-effects models provided within-sibship estimates.
The findings were published in Hypertension.
Risk for hypertensive disorders in pregnancy was higher after frozen embryo transfer compared with natural conception at the population level (7.4% vs. 4.3%, adjusted OR = 1.74, 95% CI, 1.61-1.89) and within sibships (aOR = 2.02; 95% CI, 1.72-2.39).
For fresh embryo transfer, risk was similar to natural conception at the population level (aOR = 1.02; 95% CI, 0.98-1.07) and within sibships (aOR = 0.99; 95% CI, 0.89-1.09).
“Our results highlight that careful consideration of all benefits and potential risks is needed before freezing all embryos as a routine in clinical practice,” Petersen said in the release. “A comprehensive, individualized conversation between physicians and patients about the benefits and risks of a fresh vs. frozen embryo transfer is key.”
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