Association of serum and follicular fluid SHBG levels and SHBG (TAAAA)n polymorphism with follicle size in women undergoing ovarian stimulation.

Objective. Sex hormone-binding globulin (SHBG) is the main transport protein of sex steroids. Recently, it has been found to be produced by granulosa lutein cells, suggesting a local role of SHBG in the ovary. The aim of this study was to investigate whether serum and follicular fluid SHBG levels and SHBG (TAAAA)(n) polymorphism are related to follicle size and pregnancy rate in women undergoing in vitro fertilisation. Methods. The study population consisted of 154 women with tubal and/or male-factor infertility undergoing IVF/ICSI and follicular fluid with oocytes from small (diameter <= 12 mm) and large (diameter >= 18 mm) follicles were studied. Genotyping of SHBG (TAAAA)(n) polymorphism was performed in peripheral blood samples. Serum and follicular fluids were used for hormones determination. Results. Women with short allele genotypes (with less than 8 TAAAA repeats) had higher number of small follicles compared to women with long allele genotypes (5.6 +/- 3.9 vs. 3.5 +/- 3.2 small follicles, p < 0.003). Follicular fluid SHBG levels correlated positively with serum SHBG levels (p < 0.001) and with the total number of follicles (p < 0.02). Furthermore, small follicles had higher follicular fluid SHBG concentration compared to large follicles (102.9 +/- 35.0 nmol/l vs. 85.85 +/- 34.88 nmol/l, p < 0.028). Conclusion. SHBG levels and the SHBG (TAAAA)(n) polymorphism are associated with follicle size.