OBJECTIVE: To evaluate the association between the number of oocytes collected and the number of top or good quality embryos (T/GQE) at cleavage (Day 2/3) and/or blastocyst (Day 5/6) stages.
DESIGN: Systematic review and meta-analysis.
MATERIALS AND METHODS: A literature search was performed in MEDLINE, EMBASE, Scopus, CINAHL and Web of Science for published randomized controlled trials and cohort studies until November 18th 2017. Included studies provided data on the association between the number of oocytes aspirated following ovarian stimulation for IVF/ICSI and the number of T/GQE either at the cleavage and/or blastocyst stage (primary outcome), or the number of 2PN, MII and euploid embryos (secondary outcomes). Pairwise comparisons were performed using a random effects model and by calculating standardized mean differences (SMD) between Group 1 (<4 oocytes retrieved), Group 2 (4-15 oocytes) and Group 3 (>15 oocytes). Graphical synthesis of correlations was performed and a weighted r correlation coefficient (rw) was calculated when meta-analysis was constrained by a high level of clinical and methodological heterogeneity among the studies.
RESULTS: 28 eligible studies evaluated 291,752 ART cycles. Graphical synthesis of correlations (17 studies) confirmed a strong positive association between the number of oocytes retrieved and the number of T/GQE at Day 2/3 (rw=0.791), T/GQE at Day 5/6 (rw=0.901), euploid embryos (rw=0.851), 2PN oocytes (rw=0.987), and MII oocytes (rw=0.988) (p<0.001 for all comparisons). Meta-analysis was conducted on 12 studies. In Group 2 compared with Group 1 a mean 1.4 more T/GQE at Day 2/3 (SMD [95% CI] 1.41 [0.79, 2.03]), 1.75 more 2PN (SMD [95% CI] 1.74 [0.95, 2.54]) and 2.0 more MII oocytes (SMD [95% CI] 1.99 [1.87, 2.05]) were obtained. The findings were similar comparing Group 3 to Group 1; 1.9 more T/GQE at Day 2/3 (SMD [95% CI] 1.91 [1.05, 2.77]), 3.2 more 2PN (SMD [95% CI] 3.19 [1.97, 4.40]) and 3.6 more MII (SMD [95% CI] 3.63 [2.64, 4.61]). This effect persisted when Group 3 was compared with Group 2; 1.2 more T/GQE (at day 2/3; SMD [95% CI] 1.15 [0.74, 1.55]), 1.9 more 2PN (SMD [95% CI] 1.89 [1.70, 2.08]), 1.9 more MII (SMD [95% CI] 1.89 [1.35, 2.43]) and 0.70 more euploid embryos (SMD [95% CI] 0.70 [0.55, 0.85]).
CONCLUSIONS: We found a strong positive association between the number of oocytes aspirated following ovarian stimulation for IVF/ICSI and the number of T/GQE. Furthermore, as the number of aspirated oocytes increases, the number of MII oocytes, 2PN oocytes, and euploid embryos also increase. Even though the associations observed were always positive, a high level of heterogeneity between studies warrants caution when interpreting these results.