Pregnancy outcomes in women with repeated implantation failures after intracytoplasmic morphologically selected sperm injection (IMSI)

Implantation failure is the major cause negatively influencing the outcome of assisted reproductive technologies (ART), as only two out of every ten embryos successfully implant [1]. The outcome of intracytoplasmic sperm injection (ICSI) has been shown to be positively associated with the morphological state of the sperm [2‐7], while early miscarriage rates were negatively associated with nuclear morphology [5‐7]. However, repeated failure of conventional IVF has been suggested to be caused by a paternal effect on early embryo development, a hypothesis confirmed using a shared oocyte donation model [8‐11].

Bartoov et al. [5, 12] developed a method of human spermatozoa evaluation performed in real-time at high magnification called "motile sperm organelle morphology examination" (MSOME). MSOME is performed using an inverted microscope equipped with Normarski interference contrast optics, which enables observation at high magnification (> 6000×) compared to the 200-400× observed by conventional ICSI [12]. This method led to the development of the intracytoplasmic morphologically selected sperm injection (IMSI) procedure, which is based on sperm normality as defined by MSOME classification and aims to improve conventional ICSI outcomes by focusing on the correlation between abnormalities in sperm morphology observed at high magnification and DNA damage [5, 13‐20]. Various studies have demonstrated that IMSI significantly improves fertilisation rates [21, 22], embryo quality [5, 11, 20, 21, 23], the rate of development up to the blastocyst stage [21, 24], the rates of implantation and pregnancy after embryo transfer on day 2 or 3 [5‐7, 11, 13, 20, 22, 23, 25, 26] or in the blastocyst stage [24, 27] and the likelihood of having a normal healthy child [28]; IMSI also appears to significantly decrease miscarriage rates [5‐7, 13, 23, 26, 29]. In fact, prior failures in ICSI cycles constituted an inclusion criterion in several studies employing IMSI [6, 13, 24, 28, 30].

To better comprehend the value of IMSI/MSOME, the purpose of this study was to compare laboratory and clinical outcomes of IMSI versus conventional ICSI in couples with repeated ICSI failures.

The characteristics of the study patients (general population) in both the IMSI and ICSI groups were comparable with regard to age, the number of treatment failures, aetiology of infertility, the percentage of normal form assessed by MSOME, semen parameters, the total number of oocytes collected, the number of mature oocytes collected, the total number of embryos transferred and the number of high-quality embryos transferred. No statistically significant differences (P > 0.05) were observed between the two groups with regard to rates of fertilisation (IMSI: 65.4 ± 23.5%; ICSI: 62 ± 26.5%), implantation (IMSI:13.6%; ICSI:9.8%) and pregnancy/cycle (IMSI:26%; ICSI:19%). Although not statistically significant, rates of miscarriage (IMSI:15.4%; ICSI:31.6%), ongoing pregnancy (IMSI:22%; ICSI:13%) and live births (IMSI:21%; ICSI:12%) displayed a clear trend towards better outcomes in the IMSI group. Table 1 summarises the characteristics and outcomes of the general study population.

In the subpopulation of cases with male factor (IMSI: 37 couples; ICSI: 45 couples) characteristics of study patients were comparable with regard to age, the number of treatment failures, the percentage of normal form assessed by MSOME, semen parameters, the total number of oocytes collected, the number of mature oocytes collected, the total number of embryos transferred and the number of high-quality embryos transferred. Similar to the general population, no statistically significant differences (P > 0.05) were observed between the two groups with regard to rates of fertilisation (IMSI: 59.1 ± 23.1%; ICSI: 57.8 ± 25.2%), implantation (IMSI: 11.8%; ICSI: 11.2%) and pregnancy/cycle (IMSI: 32.4%; ICSI: 24.4%). Rates of miscarriage (IMSI: 16.7%; ICSI: 36.4%), ongoing pregnancy (IMSI:27%; ICSI: 15.5%) and live births (IMSI:27%; ICSI: 15.5%) again showed a clear trend towards better outcomes in the IMSI group, although they were not considered statistically significant. These results are summarised in Table 2.

In relation to the subpopulation without male factor (IMSI: 63 couples; ICSI: 55 couples), there were no differences in patient age, the number of treatment failures, the percentage of normal form assessed by MSOME, semen parameters, the total number of oocytes collected, the number of mature oocytes collected, the total number of embryos transferred and the number of high-quality embryos transferred between the two groups. Once again, no differences (P > 0.05) were observed in rates of fertilisation (IMSI: 68.1 ± 24.4%; ICSI: 65.4 ± 27.4%), implantation (IMSI: 14.6%; ICSI: 8.6%) or pregnancy/cycle (IMSI: 22.2%; ICSI: 14.5%). As in previous analyses, rates of miscarriage (IMSI: 14.3%; ICSI: 25%), ongoing pregnancy (IMSI: 19%; ICSI: 10.9%) and live births (IMSI: 17.5%; ICSI: 9.1%) displayed a clear trend towards better outcomes in the IMSI group, although they were not statistically significant. These results are summarised in Table 2.

The aim of ART is to birth a single, healthy baby, and the success of this event depends on many variables. Despite advances in the field of assisted reproduction, implantation rates have not improved significantly since the ICSI technique was established in 1992 [36]. It is well known that implantation rates are related to endometrial receptivity, cytokines, and growth factors secreted by ovarian stimulation [37‐39]. Poor embryo quality is another important factor that negatively affects implantation rates [40]. Choosing sperm using MSOME parameters appears to provide better rates of fertilisation and embryo quality [11, 21], which also translates to better conditions during the implantation process. It is well established that the capacity of human sperm to fertilise an oocyte and produce an embryo with high potential of implantation and development depends, among other factors, on DNA integrity [15, 16]. Observations from our group have shown that the presence of large nuclear vacuoles (LNV), which are sperm-specific alterations observed at high magnification, may be related to DNA fragmentation and denaturation [15]. Vanderzwalmen et al. [24] also reported a negative impact of the presence of one large nuclear vacuole or several small vacuoles in the head of spermatozoa on the competence of embryos to develop to the blastocyst stage. Moreover, Wilding et al. [20] had suggested that a correlation exists between LNV and DNA fragmentation. Even if percentages of fertilisation and embryo development are comparable to those of conventional ICSI, embryos obtained from spermatozoa analysed by MSOME showed higher quality, and more overall pregnancies were achieved. On the other hand, recent investigations have related LNV to the absence of an acrosome reaction, which could explain the hampering of embryo development when a spermatozoon with this characteristic is chosen for microinjection [41]. Gopalkrishnan et al. [42] found that the chromatin of spermatozoa from men whose partners presented with early pregnancy loss was often compact or partially compact with irregular nuclear borders and large vacuoles.

Currently, ICSI is performed after morphological selection of spermatozoa at 200× to 400× magnification. In this magnification range, spermatozoa carrying defects of the head, neck or tail can be detected, but nuclear vacuoles cannot. Therefore, observation at a magnification of 6000× to 12,500× when selecting spermatozoa appears to be better by simply allowing precise identification of vacuoles [6, 7, 15, 16, 20, 23, 24]. Nevertheless, in couples with repeated implantation failures, sperm selection at high magnification does not appear to exert much significant influence. Fertilisation rates were similar between the IMSI and ICSI groups, a result not influenced by the presence or absence of male factor, and confirms other prior findings that also did not detect any significant differences in fertilisation rates [5, 11, 12, 23]. Regarding clinical results, there was again no significant influence of sperm selection at high magnification both in the general population and in subgroups with or without male factor. However, there was a significant and clear trend for better results in the IMSI group, particularly for rates of ongoing pregnancy, live births (both nearly doubled) and miscarriage (≈50% reduced). Although not statistically significant (likely due to sample size), these results can be considered clinically relevant. Given that apparently normal spermatozoa visualized in the low magnification range in conventional ICSI may possess hidden anomalies that could be detected at higher magnification with MSOME, the use of sperm selected by IMSI can produce embryos with higher developmental capacity. This would exclude using sperm with higher probabilities of DNA fragmentation and denaturation.

This trend is in agreement with several published studies. In addition, other investigations reported that IMSI is able to increase pregnancy rates and reduce miscarriage rates in assisted reproduction cycles [5, 11, 14, 20, 23, 26]. In a prospective randomized study comparing the clinical outcome of 87 IMSI cycles with 81 conventional ICSI cycles, Balaban et al. [25] reported that IMSI did not provide any significant improvement in the clinical outcome compared to ICSI. However, there were trends for higher rates of implantation (28.9% versus 19.5%), clinical pregnancy (54.0% versus 44.4%) and live births (43.7% versus 38.3%) in the IMSI group. On the other hand, in this same study [25], severe male factor patients were found to benefit from the IMSI procedure, as significantly higher implantation rates were observed compared to their counterparts in the ICSI group.

In conclusion, the results obtained in this investigation suggest that IMSI does not appear to provide a significant improvement in clinical outcome compared to ICSI, at least in couples with repeated implantation failures after conventional ICSI. However, it should be noted that there were clear trends for lower rates of miscarriage (≈50% reduced) and higher ongoing pregnancy and live births (nearly doubled) in the IMSI group. Thus, using morphologically-selected spermatozoa with IMSI would benefit those with poor reproductive prognosis; however, further confirmation in addition to randomized large-scale trials are still needed.

The authors declare that they have no competing interests.