Purpose: To determine the impact of nutritional supplementation on female fertility. Methods: A double blind, placebo-controlled study of the effects of FertilityBlend^® for Women, a proprietary nutritional supplement containing chasteberry, green tea, L-arginine, vitamins (including folate) and minerals, on progesterone level, basal body temperature, menstrual cycle length, pregnancy rate and side-effects. Results: Ninety-three (93) women, aged 24-42 years, who had tried unsuccessfully to conceive for six to 36 months, completed the study. After three months, the FertilityBlend^® (FB) group (N = 53) demonstrated a trend toward increased mean mid-luteal progesterone (P mi), but among women with basal pretreatment P mi <9 ng/mL, the increase in progesterone was highly significant. The average number of days with luteal-phase basal temperatures over 98°F increased significantly in the FB group. Both short and long cycles (<27 days or >32 days pretreatment) were normalized in the FB group. The placebo group (N = 40) did not show any significant changes in these parameters. After three months, 14 of the 53 women in the FB group were pregnant (26%) compared to four of the 40 women in the placebo group (10%; p = 0.01). Three additional women conceived after six months on FB (32%). No significant side-effects were noted. Conclusion: Nutritional supplements could provide an alternative or adjunct to conventional fertility therapies.