Using frozen embryos as part of assisted reproductive treatment does not increase the chances of pregnancy when compared with fresh embryo transfer, a new study published today (5 August 2020) says.
Researchers from Denmark, Sweden and Spain say their findings, which are published in The BMJ, suggest that fresh embryo transfer should be the gold standard, despite a freeze-all strategy becoming more common as it can minimise the risk of ovarian hyperstimulation syndrome.
This study examined if a freeze-all strategy resulted in a higher pregnancy rate than a fresh transfer strategy and involved 460 women, aged 18-39 years with regular menstrual cycles starting their first, second, or third treatment cycle of in vitro fertilisation (IVF) or intracytoplasmic sperm injection (ICSI) at fertility clinics at eight public hospitals in Denmark, Sweden, and Spain.
The women were randomised to one of two treatment groups, with the freeze-all group receiving gonadotropin releasing hormone to trigger egg maturity, followed by a single 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 on the day of triggering had elective freezing of all embryos and transfer was delayed as a safety measure.
Lead study author Dr Sacha Stormlund, of Hvidovre University Hospital, Denmark, said the results show that the pregnancy rate, which was defined as a detectable foetal heart beat after eight weeks of gestation, did not differ significantly between the freeze-all and fresh transfer groups, with 62 out of 223 (27.8%) in the former group compared with 68 out of 230 (29.6%).
There was also no significant difference in the live birth rate, with 61 out of 223 (27.4%) for the freeze-all group and 66 out of 230 (28.7%) for the fresh transfer group.
The researchers also found no significant differences for pregnancy loss between the two groups, while none of the women had severe ovarian hyperstimulation syndrome.
There was a higher average birth weight after frozen blastocyst transfer and an increased risk of prematurity after fresh blastocyst transfer, while time to pregnancy was longer in the freeze-all group.
The researchers say 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 the indiscriminate application of a freeze-all strategy when no apparent risk of ovarian hyperstimulation syndrome is present,” they conclude.
Stormlund S, Sopa N, Zedeler A et al. Freeze-all versus fresh blastocyst transfer strategy during in vitro fertilisation in women with regular menstrual cycles: multicentre randomised controlled trial. BMJ 6 August 2020. DOI: 10.1136/bmj.m2519
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