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Chances of pregnancy and live birth are not higher with frozen over fresh embryo transfer, finds study

The pregnancy rate did not differ significantly between the freeze-all and fresh transfer groups: 62 out of 223 or 27.8% versus 68 out of 230 or 29.6% respectively
PUBLISHED AUG 5, 2020
(Getty Images)
(Getty Images)

The chances of pregnancy are no higher with frozen over fresh embryo transfer, according to a team of researchers. The authors say that fresh embryo transfer should be the gold standard in assisted reproduction for women with no immediate risk of “ovarian hyperstimulation syndrome" which is an exaggerated response to excess hormones.

“Elective freezing of embryos is becoming more common as pregnancy rates after frozen transfers approach those of fresh transfers. A 'freeze-all strategy' can also minimize the risk of ovarian hyperstimulation syndrome (a painful response to hormones used to stimulate egg development), but studies comparing the two strategies are lacking,” say researchers. To help fill this evidence gap, the authors set out to test whether a freeze-all strategy resulted in a higher pregnancy rate than a fresh transfer strategy. The team includes experts from Hvidovre University Hospital, Denmark; Copenhagen University Hospital, Denmark; Skane University Hospital, Sweden; and Dexeus University Hospital, Spain, among others. 

The study is based on 460 women aged 18-39 years with regular menstrual cycles starting their first, second, or third treatment cycle of in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI) at fertility clinics at eight public hospitals in Denmark, Sweden and Spain. The women were enrolled in the trial between May 5, 2016, and September 7, 2018. They were randomized to one of two treatment groups: 230 were randomized to the freeze-all strategy group and 230 to the fresh transfer strategy group. 

“The freeze-all group (elective freezing of all embryos) received gonadotropin-releasing hormone to trigger egg maturity, followed by a single frozen-thawed mature egg (blastocyst) transfer. The fresh transfer group received human chorionic gonadotropin to trigger egg maturity, followed by a single fresh blastocyst transfer. Women in the fresh transfer group with an excess number of mature follicles (fluid-filled sacs containing an egg) on the day of triggering had elective freezing of all embryos and transfer was delayed as a safety measure,” says the study published in The BMJ.

Elective freezing of embryos is becoming more common as pregnancy rates after frozen transfers approach those of fresh transfers, say experts
(Getty Images)

The research team found that freezing embryos for later transfer as part of assisted reproductive treatment did not result in a higher chance of pregnancy compared with fresh embryo transfer. The analysis reveals that the pregnancy rate (defined as a detectable fetal heartbeat after eight weeks of gestation) did not differ significantly between the freeze-all and fresh transfer groups — 62 out of 223 or 27.8% versus 68 out of 230 or 29.6% respectively. The team also did not find any significant difference in the live birth rate, with 61 out of 223 or 27.4% for the freeze-all group and 66 out of 230 or 28.7% for the fresh transfer group. No significant differences between groups were observed for pregnancy loss, and none of the women had severe ovarian hyperstimulation syndrome. The risks of complications did not differ between the two groups except for a higher average birth weight after frozen blastocyst transfer and an increased risk of prematurity after fresh blastocyst transfer. Time to pregnancy was longer in the freeze-all group, shows analysis. 

“In women with regular menstrual cycles, a freeze-all strategy with gonadotropin-releasing hormone agonist triggering did not result in higher ongoing pregnancy and live birth rates than a fresh transfer strategy. A safe fresh embryo transfer strategy can be applied to women with regular menstrual cycles with strict cancellation criteria for the fresh transfer if an excess number of mature follicles are present. The findings warrant caution in applying an indiscriminate freeze-all strategy for all women undergoing assisted reproductive technology treatment when no apparent risk of ovarian hyperstimulation syndrome is present,” the team concludes.

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