Authors: Carrie Bedient, Kajal Verma, Ankita Raman, Leah Kaye, Martha Aguirre, Forest Garner, Bruce Shapiro

The Pre-Implantation Human Embryo “Remembers” the Size of the Ovarian Follicle That It Came From

Authors:

Carrie Bedient, Kajal Verma, Ankita Raman, Leah Kaye, Martha Aguirre, Forest Garner, Bruce Shapiro

Objective:

Investigate any relationship between ovarian follicle size and the rate of good blastocyst formation among successfully fertilized (bipronuclear, or 2pn) oocytes.

Materials and Methods:

This was an IRB-approved prospective observational study. Following conventional ovarian stimulation with exogenous gonadotropins, follicles were measured during oocyte collection. After insemination by intracytoplasmic sperm injection, oocytes were subsequently observed to assess fertilization. Resulting embryos were group-cultured to the blastocyst stage according to follicle size. Good blastocysts were those suitable for transfer (no “CC” grades by the Gardner system). Logistic regression was used to assess oocyte maturity, fertilization potential, and good blastocyst formation as a function of follicle size.

Results:

The results of 2,152 collected oocytes, 1,633 M-II oocytes, 1,126 2pn oocytes, and 566 good-quality blastocysts are shown in Table 1. Logistic regression of oocyte maturity vs. follicle size found increasing probability of oocytes being mature (metaphase-II) as follicle size increased (P<0.0001). Logistic regression of successful fertilization (2pn) among mature oocytes did not find a significant relationship with follicle size (P=0.1792).  Logistic regression of good blastocyst formation among all oocytes collected found the probability of blastocyst formation significantly increased as follicle size increased (P<0.0001). Logistic regression of good blastocyst formation among 2pn oocytes found the probability of obtaining a good-quality blastocyst significantly increased as follicle size increased (P<0.0001).

Conclusions:

Oocyte maturity and good blastocyst formation have positive correlations with ovarian follicle size.

Impact:

Curiously, the ability of a mature oocyte to fertilize had no clear relationship with follicle size, although subsequent development to the blastocyst stage was strongly related to follicle size.