Predictive value of the differential in nucleolar count (ND) between the pronuclei of 16–18 hour zygote and embryo quality on day 3 and 5

Abstract

Objective: To evaluate the effect of distribution patterns of nucleoli number that lead to poor, fair, or normal embryo/blastocyst development. Design: Prospective cohort study. Setting: Multi-center private practice. Patients: Infertile women <40 yrs years undergoing in vitro fertilization (IVF). Interventions: Two thousand six hundred and fifty one (2651) oocytes reached to 7–9 cell stage at 72hr post-injection were included in this study. Oocytes derived from 414 women with normal ovarian reserve who underwent In Vitro Fertilization at the Sher Institute for Reproductive Medicine (SIRM), between January 1st and December 31st, 2002 were inseminated by intracytoplasmic sperm injection (ICSI). Embryos were cultured in P1 (Irvine Scientific) for 36 hours, and then transferred to Blastocyst medium (Irvine Scientific) until embryo transfer carried on either the 3rd or 5th day post oocyte retrieval. Main Measures of Outcome: The influence of a differential in the number of nucleoli in each pronucleus of a 16–18 hour zygote [i.e. the Nucleolar Differential (ND)], on embryo quality, 3 and 5 days post retrieval. Results (Table 1): Group 1 (n= 1191, 44.9%) comprised embryos that 72hrs (Day 3) following ICSI had developed 7–9 blastomeres with no significant fragmentation (“good quality”); Group 2 (n=1214, 45.8%) comprised embryos that had 7–9 blastomeres on Day 3 with 20% fragmentation (“Fair quality”) and, Group 3 (n=216, 8.3%) comprised embryos that had attained the 7–9 blastomere stage and had >20% fragmentation (“poor quality”). One thousand and fifty three (1053/1191, 88.4%) embryos in Group 1 graded as “good quality” were derived from zygotes where the ND was 3 or less whereas 11.6% (138/1191) of embryos in the same group developed from ND 4 or more. One thousand and seventy four (88.5%) embryos in Group 2 were derived from zygotes where the ND was ≤3, and 140 (11.5%) of these from ND≥4 zygotes. In Groups 3, 87.9% embryos (190/216) derived from ND≤3 zygotes whereas 12.1% embryos (28/216) derived from ND≥4. Nine hundred and ninety seven blastocysts (36.7%) developed from oocytes which were evaluated on day 3. Of these, 884 (88.7%) developed from ND≤3 zygotes, whereas 113 (11.3%) were from ND≥4. Four hundred and eighty seven (48.8%) of these were at the blastocyst stage, whereas 510 (51.1%) were at the early blastocyst stage. Two hundred ninety six (29.7%) were selected for freezing based on their day 5 quality. Of these, 266 (89.9%) developed from ND≤3 zygotes, whereas 31 (10.1%) were from ND≥4 zygotes. Conclusions: Similar proportions of ND are seen in day 3 and 5 embryos of “good”, “fair”, and “poor” quality. Therefore, the difference in nucleoli counts does not appear to be predictive of a zygote developmental potential at 16–18 h post-insemination.