Z scores of embryos at the pronuclear stage are not predictive of IVF pregnancy outcome

Abstract

OBJECTIVE: Pronuclear scoring (Z score) has been reported to predict the quality of oocytes and implantation (Scott et al. Hum. Reprod. 15:2394-403 2000). We have instituted the Z-scoring system in our facility without using it to select embryos for transfer. Our objective was to compare Z scores for embryos that we know implanted or did not implant in situations for which the uterus was demonstrably receptive. DESIGN: Retrospective Analysis of Laboratory Records. MATERIALS AND METHODS: Z scores were assessed (1 = “best”, 2, or 3 = “worst”) at the time of fertilization scoring (16-18 hours after insemination; generally by ICSI). Z scores for embryos from IVF patients between 1/1/02 and 5/31/06 with known outcomes have been compared for 3 groups. We assured correct tracking of embryos from Z scoring to transfer by including only patients for whom all fertilized oocytes were transferred on day 3. No patient had more than 5 fertilized oocytes (2.8 ± 0.93 per patient). For Group I (6 patients), ALL embryos implanted. For Group II (34 patients), at least one but not all of the embryos implanted. For Group III (58 patients), None of the embryos implanted. By comparing Groups I and II, embryos that implanted (Group I) were compared with embryos that did not implant (Group II) while only considering patients for whom the uterus was demonstrably receptive. Group III yields information about the range of Z scores found in embryos regardless of outcome. RESULTS: Z-scores (mean ± S.D.) averaged 2.11 ± 0.93 (n=9) for Group I, 2.06 ± 0.84 (n=93) for Group II and 2.06 ± 0.85 (n=162) for Group III. The 3 groups were not different (ANOVA F=0.012; P>0.05). Therefore, Group I was not significantly different than Group II. Note that the standard deviations for all three groups are quite comparable, indicative that the distribution of scores is equally broad across all three groups. Similarly, we compared the numbers of nucleoli in a) the PN with more nucleoli (6.4 ± 1.6, n=61) and b) the PN with fewer nucleoli (3.9 ± 1.6, n=61), the difference in numbers of nucleoli between the two PN (2.5 ± 1.6; n=61) and the number of polar bodies (2.13 ± 0.40, n=274). No significant differences existed between Groups I and II or between Groups I and III for these parameters (ANOVA). Groups II and III differed significantly in only one category: number of nucleoli in PN with more nucleoli. CONCLUSIONS: In our program, neither Z scores nor numbers of nucleoli were predictive of implantation when controlled for the presence of a receptive uterus.