Natural ovulation is the best option before IVF frozen embryo transfer

Natural ovulation is as effective as hormone treatment for preparing the uterus for frozen embryo transfer after in vitro fertilization (IVF) and carries fewer risks, according to a large, randomized trial.

New evidence suggests that in women who respond well to IVF (by being able to produce lots of eggs), freezing embryos and transferring them later in the cycle can increase the success rate. As a result, frozen embryo transfers now account for the majority of embryo transfers worldwide.

After IVF, the frozen embryo must be transferred to the uterus at the precise point in the menstrual cycle when the endometrium—the blood vessel-rich inner lining of the uterus—is strong enough to support implantation.

Women can choose either a medicated cycle, where estrogen and progesterone are taken throughout the month to prepare the uterus, or their natural cycle, if it is regular, which relies on monitoring the hormones produced by the body.

Which choice is best has remained somewhat of a mystery because no previous study has been large enough to assess the complications associated with the different methods.

To solve this, Daimin Wei at Shandong University in Jinan, China, and her colleagues conducted a large study involving 4,376 women at 24 fertility centers. All participants were between the ages of 20 and 40 and planned to undergo a single frozen embryo transfer. Half were assigned a medicated protocol, the other half used their natural cycle.

“This is the randomized controlled trial we’ve been waiting for,” he says William Buckett at McGill University in Montreal, Canada, who did not participate in the study.

Birth rates were similar in the two groups, at 41.6 percent for the natural cycle and 40.6 percent in the treatment group, suggesting that natural ovulation is as effective as hormone treatment in preparing the uterus for implantation.

However, distinct differences emerged when examining maternal complications during and after pregnancy.

Women using their natural cycle had a lower risk of preeclampsia, a potentially life-threatening condition characterized by high blood pressure, and experienced fewer early pregnancy losses. They were also less likely to develop the spectrum of placenta accreta, a condition in which the placenta cannot separate easily after birth. There was also a lower incidence of cesarean sections and severe postpartum hemorrhage in this group.

“These risks not only affect maternal and fetal health during pregnancy, but are also associated with long-term health after delivery,” says Wei.

“This is an important new study,” he says Tim ChildChair of the UK Human Fertilization and Embryology Authority’s Scientific and Clinical Advancement Advisory Committee. Clinics currently advise people with regular cycles that natural and medicated approaches have equal success rates, she says.

However, Child adds, there has been some suggestion that natural cycles lead to lower rates of preeclampsia. This may be due to the presence of the corpus luteum, a temporary structure in the ovary that forms after ovulation and produces hormones that help prepare the uterus for pregnancy, which may affect the risk of preeclampsia.

“This very large study confirms and expands on previous findings and suspicions, notably a significantly lower incidence of preeclampsia, early pregnancy loss, placental abruption, caesarean section and postpartum haemorrhage. [with the natural cycle route]” says Child.

Wei’s team now intends to examine the blood samples taken during the study to identify potential biomarkers that could explain the differences in pregnancy complications.

topics: