Relationship between follicle size and ultrasound-guided transvaginal oocyte recovery

We evaluated the relationship between follicle size and oocyte recovery (OR ) using ultrasound-guided follicle aspiration. Thirty Holstein cows were su bjected to OR without gonadotrophic therapy. Oocytes were recovered two to four times from each cow in a total of 67 aspiration sessions, Ovarian foll icles with diameters less than or equal to4 mm and >4 mm were aspirated in separated groups. Recovered oocytes from each group were kept separate and submitted to in vitro maturation, fertilization, and culture to the blastoc yst stage. A total of 430 follicles were aspirated, of which 154 (35.8%) we re from follicles >4 mm and 276 (64.2%) were from follicles less than or eq ual to4 mm. Seventy-seven oocytes (50%) were recovered from follicles >4 mm and 200 (72.2%) were from follicles less than or equal to4 mm. Nineteen bl astocysts were obtained from follicles >4 mm, whereas 45 blastocysts were o btained from follicles less than or equal to4 mm. Recovery rate was greater (P < 0.01) in follicles less than or equal to4 mm, Oocyte quality, cleavag e rate and blastocyst development did not differ between different follicle sizes. Routine aspiration of small follicles (less than or equal to4 mm) c ould increase the number of oocytes available for in vitro development. (C) 2001 Elsevier Science B.V. All rights reserved.