Human follicular fluid-induced acrosome reaction predicts sperm fertilizing ability in vitro

Abstract

To study the relationship between follicular fluid induced acrosome reaction (FFIAR) and fertilizing ability of human sperm in vitro. Retrospective review and comparison of 1,106 in vitro Fertilization (IVF) cycles between January 2001 and August 2004. 797 cycles used conventional IVF, 153 used Intracytoplasmic Sperm Injection (ICSI), and 156 used a combination of both. Couples with fewer than 3 mature oocytes or sperm antibody in either partner were not included in the study. Standard methods were used for ovarian stimulation and embryology. Semen was obtained by masturbation on the day of oocyte retrieval. To study the acrosome reaction, motile sperm were selected by swim-up. Capacitated sperm were incubated for 18–22 hours with follicular fluid then washed. The smear was stained for 30 minutes with Pisum sativam agglutinin labeled with fluorescein. Analysis was done at 400× on a fluorescence microscope. When more than half the head of a spermatozoa was brightly and uniformly fluorescing, the acrosome was considered to be intact. Spermatozoa without fluorescence or with a fluorescing band limited to the equatorial segment were considered to have undergone an acrosome reaction. The significance of differences between groups was determined by χ2 analysis. Control specimen AR values ranged from 0–18 with an average value of 2.02 ± 1.97, FFIAR AR values ranged from 0–48.5 with an average of 10.43 ± 8.48. In the conventional IVF Group, 22 patients had AR values of <2, while 775 patients had AR values ≥2. When conventional IVF was used to inseminate oocytes, there was a significant reduction in fertilization rate (48.8% vs. 70.4%, P<0.01) when the AR value was found to be <2. When ICSI was used to inseminate oocytes, there was no difference in fertilization rate regardless of the AR score. In addition, in the IVF only group, there were 2 out of 22 complete failures of fertilization in the group with AR values <2 (9.1%), vs. 8 out of 775 (1%) from the group with AR values ≥2. There were no failures of fertilization when ICSI was used. In the combined IVF/ICSI group, fertilization rate was lower in the IVF vs. ICSI oocytes (39.3% vs. 70.2%, P<0.05) when the AR rate was <2. FFIAR can be utilized to predict the fertilizing ability of human sperm in vitro. When FFIAR is <2% ICSI should be employed to ensure high rates of fertilization and a low number of failed fertilizations.