Abstract The prevalence of the isolated ultrasonographic finding of polycystic ovaries (PCO) in the Finnish population and among women with a history of gestational diabetes (GDM) and changes in the present carbohydrate metabolism were investigated in the present study. One aim of this study was to investigate the prevalence of the recently discovered variant type LH (v-LH) in PCOS and to compare patient cohorts from Finland, the Netherlands, the United Kingdom and the United States of America. In addition, this study attempted to evaluate the nature of the ovarian streoidogenic response of women with PCOS to exogenously administered human chorionic gonadotrophin (hCG), human menotrophin (hMG) and follicle stimulating hormone (FSH). The effect of metformin on ovarian steroidogenesis was also studied. The prevalence of PCO was significantly higher in younger (≤ 35 years, 21.6%) than among older women (in ≥ 36 years, 7.8%). The overall prevalence of PCO in Finnish women was 14.2%. Women with previous GDM revealed a high prevalence of PCO (39.4%). The carrier frequency of the v-LHb allele in the entire study population was 18.5%. The frequency of the v-LH carrier was significantly lower in obese PCOS subjects in the Netherlands (2.0%) and Finland (4.5%). Women with previous GDM had impaired insulin sensitivity and β-cell function. They also had higher adrenal androgen secretion than the control women. Women with PCO and previous GDM had marked hyperinsulinemia which was not explained by obesity. Obese PCOS women achieved peak peripheral serum T concentrations at 48 hours after a hCG injection, preceded by peak levels of 17-OHP and E2 at 24 hours. In contrast, all steroids measured in the control women reached their maximum serum concentrations at 96 hours. HMG stimulated the production of ovarian androgens more efficiently than a urinary FSH after pituitary suppression with a gonadotrophin releasing hormone agonist (GnRHa). In conclusion, the prevalence of PCO is common in healthy Finnish women and even more common in women with a history of GDM. The ultrasonographic appearance of PCO may be a predictive factor with regards abnormal glucose tolerance during and after pregnancy and, these women should therefore be advised as to possible consequences. The high overall frequency of the v-LH allele in women in general and its low frequency in obese PCOS patients suggests that v-LH plays a role in reproductive functions and may counteract the pathogenesis of PCOS in obese individuals. The differences observed in steroid responses to hCG between normal and PCOS women might be explained by higher theca cell activity or mass in polycystic ovaries. Women with PCOS did not show a distinctly exaggerated steroidogenic response to hMG or FSH administration compared with control women. FSH administration also resulted in increased A and T production.