COPENHAGEN — While single-embryo transfer rates for in vitro fertilization procedures languish below 2% in the United States, the Europeans are hitting astonishing highs with impressive results.
Aimed at reducing the growing multiple-pregnancy rate—which was once accepted as an unavoidable side effect of invitro fertilization (IVF)—single-embryo transfer (SET) has been enthusiastically embraced across much of Europe, particularly in the Nordic countries and Belgium. Indeed, SET made up 70% of Swedish embryo transfers last year, said Anders Nyboe Andersen, M.D., at the annual meeting of the European Society of Human Reproduction and Embryology.
The latest European figures (2002) show that of all clinical pregnancies achieved using assisted reproductive technology (ART), the rate of triplet pregnancies per transfer was just over 1%, and the rate of twin pregnancies per transfer was 23.6%, he said.
According to a 2002 report from the Centers for Disease Control and Prevention, the risk of having a pregnancy involving triplets or more per ART cycle was almost 7%, and the risk of a twin pregnancy was 29%. Dr. Andersen, head of the fertility clinic at the Rigshospitalet at Copenhagen University Hospital, noted that because of reporting differences, the U.S. and European data were not directly comparable.
Many fertility experts initially regarded SET as a necessary compromise: The possibility of multiple pregnancies was decreased at the price of a decrease in pregnancy rates overall. Indeed, supporters of this theory have pointed out that the failure of the United States to adopt the widespread use of SET has worked to the advantage of the overall rate of clinical pregnancies per ART cycle in the United States, which is 34.3%, about 5% higher than the European rate.
But the recent Swedish experience has vindicated SET in this regard, reported Karin Erb, laboratory director, fertility clinic, Odense (Denmark) University Hospital.
In a review of fertility data from the Nordic countries, which she presented at the meeting, Ms. Erb reported that stricter Swedish embryo transfer legislation introduced in 2003 forced a sharp increase in SET in that country, with no decrease in the country's overall IVF success rates.
Preliminary 2004 data for Sweden is “even more exciting,” said Professor Karl Nygren of the department of obstetrics and gynecology at Sofiahemmet Hospital in Stockholm.
“The pregnancy rate per embryo transfer remained constant at around 30%, while the number of twin births plummeted to just 5%, and there were no triplet deliveries at all,” he said in a written statement.
While SET becomes the standard of care in many European countries, fertility experts in the United States continue to regard it as a rarity.
“This is amazing. I didn't even know they were doing this,” Jeffrey M. Jones, Ph.D., director of the andrology and IVF laboratory at the University of Wisconsin Medical School in Madison, commented in an interview after hearing some of the presentations at the meeting.
In 2002, SET made up just 1.2% of all IVF and intracytoplasmic sperm injection cycles in the United States, up from 0.8% in 2001. In 2004, for the first time, guidelines released by the American Society for Reproductive Medicine and the Society for Assisted Reproductive Technology recommended that SET be considered “for patients with the most favorable prognosis” (Fertil. Steril. 2004;82:773–4). The effect of those guidelines, however, will not be seen before the release of the 2005 data.
Certainly, not all centers can adopt SET without seeing at least an initial decrease in pregnancy rates—and patient selection is a key factor in this equation.
The world's first randomized trial comparing SET to double-embryo transfer (DET) in unselected patients is a case in point.
At the meeting, Aafke van Montfoort, M.D., of the Academic Hospital Maastricht (the Netherlands) reported data on 308 patients under age 41 who were randomized to SET or DET for their first IVF cycle. There were no twins in the SET group, compared with a twin rate of 21% in the DET group. The ongoing pregnancy rate was considerably lower after SET, however, at 21% vs. 40%, said Dr. van Montfoort.
But in another study presented at the meeting, patients were selected (aged less than 37, two top-quality embryos, and less than 20% embryo fragmentation), and given the choice of either SET or DET. The SET group had an ongoing clinical pregnancy rate of 39%, compared with 36% in the DET group, reported H.E. Bredkjaer, M.D., of Holbaek (Denmark) Sygehus Fertility Clinic.
According to many experts, it is important to judge SET beyond the context of the first fresh IVF cycle, because the approach often yields many frozen embryos, which can boost a patient's overall chances for pregnancy.