Can polarised light microscopy (PLM) be used as a non-invasive tool for selecting the optimal sperm for ICSI?

Abstract

Aim:

To investigate PLM as a reproducible non-invasive method in the assessment of sperm head retardance, and observing PLM within a clinical setting to select an optimal sperm for ICSI.

Methods:

1. PLM (OosightTM) images from 368 spermatozoa were assessed to establish intra and inter-observer variation.

2. A range and frequency of head retardance was developed from pooled samples and then analysed further comparing normal and abnormal head morphology.

3. Normal sperm selected for ICSI according to the W.H.O 5th edition, were imaged prior to injection. Images were analysed later-blinded to the ICSI outcome. Single embryo culture and elective single blastocyst transfer (eSET) were undertaken. PLM retardance was compared with embryo fertilisation, cleavage, blastulation, utilisation and clinical pregnancy rates using independent sample T tests, Pearson's correlation coefficients, ROC curves and X2 tests.

Results:

1. The intra/inter-observer variation revealed our method to be reproducible by an Intra-class correlation coefficient and Pearson's co-efficient P<0.05.

2. The pooled sperm sample had mean retardance 0.97 +/-0.27nm, range 0.49-1.89nm. When comparing the range with head morphology it was found that retardance significantly decreases with normality (P<0.05).

3. 63 fresh and 38 frozen cases were analysed. 486 oocytes were injected and 364 fertilised (74.9%). 101 cumulative fresh and subsequent frozen single blastocysts were transferred (eSET) to produce 34 clinical pregnancies, 33.7% per Tx, 54.0% per case (fresh and frozen per OPU). There were no significant differences (P>0.05) in sperm retardance when comparing normally fertilised oocytes against either abnormal/nil fertilisation. Good quality embryos had lower retardance (P<0.05) where ≤0.91nm was optimum. There were no significant differences (P>0.05) in retardance when comparing blastulation and failed blastulation, however utilised embryos had lower retardance compared to discarded embryos (P<0.05). Embryos with lower retardance were more successful (P<0.05) at clinical pregnancies where ≤0.91nm was optimum.

Conclusion:

PLM head retardance is a reproducible non-invasive method of assessing sperm. Our results suggest sperm with head retardance ≤0.91nm are more likely to result in a clinical pregnancy. In a prospective manner, selecting sperm with lower sperm retardance may result in more embryos with good quality in culture and higher clinical pregnancy rates.