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Blastocystmorphometryis Predicted by the Diameter of the Originating Ovarian Follicle

petri dish

Authors: Bruce Shapiro, Ankita Raman, Forest Garner, Martha Aguirre, Chelsea Morrison, Shyni Thomas, Anike Bill, Carrie Bedient

Objective: Fewer trophectoderm (TE) cells and smaller inner cell masses (ICMs) have been associated with increased risks of implantation failure and early pregnancy loss.  This study will assess relationships, if any, between blastocyst morphometry and the diameter of the follicle from which the oocyte originated.

Design: IRB-approved prospective observational cohort study.

Materials and Methods:Patients underwent routine ovarian stimulation with exogenous gonadotropins. During oocyte collection, follicle diameters were sonographically measured on two perpendicular axes, and the mean of these two measurements was calculated for each follicle.Embryos were group-cultured to the blastocyst stage according to mean follicle diameter (≤9.5, 10-12.5, 13-15.5, 16-18.5, 19-21.5, 22-24.5, 25-27.5, and ≥28mm). Analysis of variance was used to compare inner cell mass (ICM) size (expressed as cross-sectional area) and trophectoderm (TE) perimeter cell counts across follicle diameter groups.Significant overall tests were followed by means comparisons. P<0.05 was considered significant.

Results: There were 566 blastocysts of good quality and 540 of these were derived from measured follicles, while 26 blastocysts derived from oocytes of uncertain or unmeasured follicular origin were excluded. Analysis of variance found a significant overall difference in ICM areas among follicle size groups (P<0.05).  Subsequent comparison of means found that follicle groups ≥16mm in mean follicle diameter were associated with significantly larger ICM sizes when compared to other follicle size groups.  Analysis of variance found a significant overall difference in TE perimeter cell counts among follicle size groups (P<0.05). Subsequent comparison of means found that follicles 10-12.5mm in mean follicle diameter were associated with significantly fewer TE perimeter cells when compared to other groups.

Conclusions: Among formed blastocysts, those derived from small ovarian follicles (<16mm) tend to have inferior morphometry (smaller ICM or fewer TE cells) when compared to those derived from larger ovarian follicles. This suggests that transfers of blastocysts derived from small follicles might have increased risk of inferior outcomes due to inferior morphometry and morphology.  These differences may clarify relationships between folliculogenesis and embryogenesis.

Support: None

Mean follicle diameter Formed Blastocysts ICM Area (µm2) TE perimeter cell count
≤9.5mm 17 2990 ± 223 15.9 ± 1.1
10-12.5mm 47 3201 ± 134 14.4 ± 0.6
13-15.5mm 82 3230 ± 101 17.0 ± 0.5
16-18.5mm 125 3473 ± 82 16.6 ± 0.4
19-21.5mm 124 3321± 83 17.0 ± 0.4
22-24.5mm 96 3422 ± 95 17.7 ± 0.5
25-27.5mm 33 3755 ± 162 17.2 ± 0.8
≥28mm 16 3580 ± 230 16.2 ± 1.1