Clinical use of a pronuclear stage score following intracytoplasmic sperm injection: impact on pregnancy rates under the conditions of the German embryo protection law

The German embryo protection law does not allow embryo selection, but only selection of pronuclear stage (PN) oocytes. Only as many PN oocytes are allowed to be selected as are planned to be transferred. Therefore, a clinically applicable score to assess the quality of PN oocytes would be helpful. A recently published score was used under the conditions of the German embryo protection law in 74 non-selected, consecutive intracytoplasmic sperm injection cycles. Only criteria which could be evaluated at the PN stage were included, i.e. not criteria which could only be assessed after pronuclear membrane breakdown or the first cleavage division. Supernumerary PN oocytes were cryopreserved after selection. A mean PN score of <13 (sum of scores of all selected PN oocytes/number of selected PN oocytes) led to a pregnancy rate of 4%, a mean PN score of > or =13 to a pregnancy rate of 22%. Embryo morphology and cumulative PN were correlated (r = 0.52, P < 0.05). The negative predictive value was 92% at a threshold of 13 for the mean PN score. The use of this and perhaps additional scoring systems of PN stage oocytes might help to offer patients in Germany the transfer of two selected PN oocytes, which would reduce the multiple pregnancy rate.