Number of embryos for transfer following in-vitro fertilisation or intra-cytoplasmic sperm injection

The traditional reliance on the transfer of multiple embryos during in vitro fertilisation (IVF) in order to maximise the chance of pregnancy, has resulted in increasing rates of multiple pregnancies. Women undergoing IVF had a 20 - fold increased risk of twins and 400 - fold increased risk of higher order pregnancies (Martin 1998). The maternal and perinatal morbidity and mortality as well as national health service costs associated with multiple pregnancies is significantly high in comparison with singleton births (Luke 1992; Callahan 1994; Goldfarb 1996). Single embryo transfer is now being considered as an effective means of reducing this iatrogenic complication. This systematic review evaluates the effectiveness of elective two embryo transfer in comparison with single and more than two embryo transfer following IVF and ICSI (intra cytoplasmic sperm injection) treatment.

The aim of this review is to determine, whether in couples who undergo IVF/ICSI: (1) the elective transfer of two embryos improves the probability of livebirth compared with: (a) Single embryo transfer, (b) Three embryo transfer or (c) Four embryo transfer.(2) the elective transfer of three embryos improves the probability of livebirth compared with: (a) Single embryo transfer, or (b) Four embryo transfer,

We searched the Cochrane Menstrual Disorders and Subfertility Group's trials register (searched June 2003), the Cochrane Central Register of Controlled Trials (The Cochrane Library, Issue 4, 2003), MEDLINE (1970 to 2003), EMBASE (1985 to 2003) and reference lists of articles. We also handsearched relevant conference proceedings and contacted researchers in the field.

Only randomised controlled trials were included.

Two reviewers independently assessed eligibility and quality of trials.

We found no studies that compared a policy of transferring multiple embryos on one cycle versus a policy of cryo- preservation and transfer of a single embryo over multiple cycles. We also found no trials comparing transfer of two versus three embryos. Three small, poorly reported trials compared transfer of two versus one embryo in a single cycle, and one small, poorly reported trial compared transfer of two versus four embryos in a single cycle. The clinical pregnancy rate per woman/couple associated with two embryo transfer was significantly higher compared to single embryo transfer (OR 2.08, 95% CI 1.24 to 3.50; test for overall effect p = 0.006). The live birth rate per woman/couple associated with two embryo transfer was also significantly higher than that associated with single embryo transfer (OR 1.90, 95% CI 1.12 to 3.22, test for overall effect p=0.02). The multiple pregnancy rate was significantly lower in women who had single embryo transfer (OR 9.97, 95% CI 2.61 to 38.19; p = 0.0008). The effectiveness of double embryo transfer versus four embryo transfer was tested in a single trial. There was no statistically significant differences in the clinical pregnancy rate (OR 0.75, 95% CI 0.26 to 2.16; p=0.6), and multiple pregnancy rates (OR 0.44. 95% CI 0.10 to 1.97; p = 0.28) between the two groups. The livebirth rate in the four embryo transfer group was higher compared to the two embryo transfer group, but the results were not statistically significant (OR 0.35, 95% CI 0.11 to 1.05; p = 0.06).

The results of this systematic review suggest that live birth and pregnancy rates following single embryo transfer are lower than those following double embryo transfer as are the chances of multiple pregnancy including twins. As such, it is unlikely that the conclusions are robust enough to catalyse a change in clinical practice. The studies included are limited by their small sample size, so that even large differences might be hidden. Cumulative livebirth rates are seldom reported. The data were inadequate to draw conclusions about single embryo transfer and first frozen single embryo transfer (1FZET) or subsequent single frozen embryo transfers. Until more evidence is available single embryo transfer may not be the preferred choice for all patients undergoing IVF/ICSI. Clinicians may need to individualise protocols for couples based on their risks of multiple pregnancy. A definitive pragmatic, large multi centre randomised controlled trial comparing single embryo versus double embryo transfer in terms of clinical and cost effectiveness as well as acceptability is required. The primary outcome measured should be cumulative livebirth per woman/couple.