In vitro fertilization (IVF) using frozen embryos may be associated with a 74% higher risk of hypertensive disorders in pregnancy, according to new research published today in Hypertension, an American Heart Association journal. In comparison, the study found that pregnancies from fresh embryo transfers — transferring the fertilized egg immediately after in vitro fertilization (IVF) instead of a frozen, fertilized egg — and pregnancy from natural conception shared a similar risk of developing a hypertensive disorder.
High blood pressure during pregnancy often signals preeclampsia, a pregnancy complication including persistent high blood pressure that can endanger the health and life of the mother and fetus. Approximately 1 out of every 25 pregnancies in the United States results in preeclampsia, according to the American Heart Association.
One IVF treatment process available utilizes frozen embryos: after an egg is fertilized by sperm in the lab, it is frozen using a cryopreservation process before being thawed and transferred to the uterus at a later date. The procedure is becoming more common because of the significantly improved freezing technology or cryopreservation methods that started in the late 2000s and because more patients are choosing to freeze embryos, according to the study authors. Yet, frozen embryo transfer is known to be associated with a higher risk of hypertensive disorders in pregnancy than both natural conception and fresh embryo transfer. However, prior to this study, it was unknown whether this was due to the freezing process or a risk factor from the parents.