Introduction Preimplantation genetic diagnosis (PGD) for chromosomal alteration and single-gene disorders (of maternal origin) using the first polar body (IPB) is the only approach possible in Italy where by Law inseminated/fertilized oocytes and embryos cannot be manipulated. Only after have obtained the genetic diagnosis of each single oocyte (which takes between 4 to 8 hours), insemination can be performed. Thus, to avoid oocyte ageing the biopsy is normally performed soon after pick-up, which means between 35 to 37 hours post hCG administration (Gianaroli et al., 2007). In this study we investigated the usefulness of polarized microscopy to evaluate oocyte maturation stage (by assessing meiotic spindle configuration) prior to IPB biopsy. Methods All patients undergoing an ICSI-PGD cycle on IPB for single-gene disorder in our centre between September and December 2008 were enrolled in this study. Oocyte retrievals were performed 35 hours post-hCG administration and oocyte denudation one hour later. Meiotic spindles were assessed immediately after denudation with Oosight system (CRi, Woburn, USA) followed by IPB biopsy. ICSI was finally performed on selected oocytes (maximum of 3 per patients according to the Law), between 6-8 hours post-biopsy, when diagnosis were available. Results A total of 60 cumulus-oocyte complexes have been obtained, of which 39 displayed a IPB and were thus suitable for biopsy. When observed at polarized light microscopy 15 (38.4%) were at Metaphase II (MII) stage with a clear meiotic spindle in the oocyte cytoplasm, 13 (33.3%) were at Telophase I (TI) stage with a meiotic spindle in between the IPB and oocyte cytoplasm and in 11 oocytes (28.2%) no spindle was detectable. Polar body biopsy was successful in all MII stage oocytes (15/15) and all oocytes without meiotic spindle detectable (11/11), while in the TI group 3/13 oocytes degenerated (23.1%) due to cytoplasmic continuity and rupture during biopsy (P=0.04). Successful DNA amplification was obtained in 12/15 MII oocytes, 4/10 TI oocytes and 4/11 oocytes without MS detectable (P=0.04). The fertilization rate with the selected MII oocytes was 80.0%. In one case two TI oocytes were used for ICSI (due to lack of availability of healthy MII) and both developed to 1PN oocytes. Conclusions When IPB biopsy has to be performed, the use of polarized light microscopy is useful to asses oocyte nuclear maturity which influences the outcome of the procedure in terms of oocyte survival and successful DNA amplification. In particular, TI oocytes may be damaged during biopsy resulting in oocyte degeneration. It can also be supposed that, in case of survival, the chromosomal arrangement of TI oocytes may be disrupted during aspiration. It is suggested that timing of PB biopsy should be adapted according to oocyte nuclear maturation stage assessed by polarized light microscopy.