Microinjection: choice of embryo transfer technique

Abstract

Subzonal sperm microinjection (SUZI) is indicated in severe oligoasthenozoospermia, in which the total count of motile sperm is inadequate for in vitro fertilization (IVF), and in cases with repeated failure of fertilization. Sperm for microinjection are selected following centrifugation on a Percoll gradient and stimulation with pentoxifylline and 2-deoxyadenosine. Motile sperm (2-10 per egg) are injected into the perivitelline space and fertilized oocytes are then cultured for two days prior to transfer into the Fallopian tube (tubal embryo stage transfer, TEST) or uterus. During 1992, SUZI results showed a total fertilization rate of 30% (19% were 2 pronuclear, 11% were polyspermic), a transfer rate of 55% and pregnancy rates of 15.2% per transfer and 8.3% per cycle. Recent pregnancy data in mild-moderate male factor infertility showed that gamete intrafallopian transfer (GIFT) results were consistently superior to TEST or IVF, suggesting a beneficial effect of the tubal environment on fertilization and early embryonic development. Accordingly, the combination of SUZI followed by the immediate transfer of injected oocytes into the Fallopian tube, the MIFT procedure, was explored. An initial study of 21 consecutive microinjection candidates showed a clinical pregnancy rate of 24% per cycle. Information regarding fertilization and polyspermy rates was available from supernumerary oocytes in 90% of patients. A randomized, controlled trial comparing MIFT with SUZI or TEST in severe male factor infertility is required to confirm the improved pregnancy rate in MIFT cycles.