Intracytoplasmic morphologically selected sperm injection (IMSI) is a variation of ICSI that uses a higher-powered microscope to select sperm. This allows embryologists to look at the sperm in greater detail (including the nucleus which contains the sperm’s genetic material). Some studies suggest that using this technique selects better quality sperm and results in higher pregnancy rates and lower miscarriage rates compared to conventional ICSI.
The shape of the sperm (morphology) is important in diagnosing male fertility problems and in predicting fertilization and pregnancy outcomes – and studies have shown that selecting better shaped sperm does improve ICSI outcomes.
In conventional ICSI, the embryologist selects the most normal-looking motile sperm using a microscope that magnifies the sample up to 400 times. IMSI is a variation of ICSI that uses a high power light microscope (enhanced by digital imaging) to magnify the sperm sample over 6000 times. This allows the embryologist to detect subtle structural alterations in sperm that a normal microscope could not detect. Sperm are then selected which have the most normally-shaped nuclei.
The technique for examining sperm to use in IMSI was developed by a team led by Professor Bartoov from Israel. In 2002, his team used a high-powered microscope to determine which morphological characteristics of sperm might affect the outcome of ICSI. They suggested that ICSI pregnancy rates may be affected by subtle abnormalities in the shape of the sperm nucleus which embryologists may not detect during normal ICSI sperm selection.
In 2003, the same group published a study that looked at whether selecting sperm using IMSI improves the pregnancy rate in couples with repeated ICSI failures (compared to conventional ICSI). The study compared 50 couples in each group. They found that the couples who underwent IMSI had a significantly higher pregnancy rate (66%) than those who underwent conventional ICSI (33%). However, this was a small sample size.
These findings were repeated in 2006 in another comparative study between 80 couples who underwent IMSI (matched with couples who underwent standard ICSI). The pregnancy rate was significantly higher (60% vs 25%) and the miscarriage rate significantly lower (14% vs 40%) in the IMSI group compared to the conventional ICSI group. However, this study was also based on a small sample size. In addition, even within the IMSI group, couples who had embryos created using sperm with normally-shaped nuclei had higher pregnancy rates and lower miscarriage rates compared to other couples in the IMSI group whose embryos were created using sperm with minor abnormalities in shape (because no normally shaped sperm were available).
Hazout et al. (2006) also found a significant improvement in implantation, pregnancy and birth rates using IMSI in patients with two or more previously unsuccessful ICSI attempts.
An Italian group carried out a prospective randomised controlled trial in 2008 to compare the outcomes of IMSI with conventional ICSI in patients with severe male factor infertility (oligoasthenoteratozoospermia). Unlike previous studies this study looked at the effect of IMSI on patients, regardless of whether they had previous unsuccessful ICSI cycles or not. The study involved 446 couples who were randomly assigned either to the ICSI study group (219 couples) or the IMSI study group (227 couples). The researchers also created three sub-groups: no previous ICSI cycles; one previous unsuccessful cycle; and two or more previous unsuccessful cycles. The study found that couples across the whole IMSI group had a significantly higher pregnancy rate (39.2%) than the ICSI group (26.5%) and the difference was most noticeable in patients with two or more previous unsuccessful cycles.
The pregnancy rates for these patients were 29.8% in the IMSI group compared with 12.9% in the ICSI group. The miscarriage rates for these patients were also significantly lower in the IMSI group (17.4%) compared with the ICSI group (37.5%).
The majority of these studies have been carried out in Israel, Italy and France and according to a report from Eppendorf (the company that manufactures the products for IMSI) in 2008, 500 babies had been born in Israel after IMSI treatment and more than 200 in Europe.
The use of IMSI is limited by the resources needed to carry out the technique. IMSI takes a minimum of 60 minutes and more often takes several hours. In addition the technique involves special equipment to reach the necessary magnification, it has to be carried out by experienced embryologists trained in the specific technique, and this explains the significant extra cost of providing IMSI.
De Vos A et al. (2003) Influence of individual sperm morphology on fertilisation, embryo morphology, and
pregnancy outcome of intracytoplasmic sperm injection. Fertil Steril 79: 42-8
Bartoov B et al. (2002) Real-time fine morphology of motile human sperm cells is associated with IVF-ICSI outcome. J Androl. 23 (1):1-8
Bartoov et al. (2003) Pregnancy rates are higher with intracytoplasmic morphologically selected sperm injection than with conventional intracytoplasmic injection. Fertil Steril 80(6): 1413-9
Berkovitz et al. (2006) How to improve IVF-ICSI outcome by sperm selection Reprod Biomed Online 12(5): 634-8
Hazout A et al. (2006) High magnification ICSI overcomes paternal effect resistant to conventional ICSI. Reprod Biomed Online 12: 19-25
Antinori M et al. (2008) Intracytoplasmic morphologically selected sperm injection: a prospective randomized trial Reprod Biomed Online 16(6): 835-41
Bartoov B (2008) Intracytoplasmic morphology selected sperm injection (IMSI/BFS) – an advanced technique for ICSI Eppendorf Applications Note 190 June 2008 www.eppendorf.com