To assess the value of serum LH measurements in early and late follicular phase as predictors of ovarian response and IVF outcome in patients treated with recombinant FSH with GnRH agonist (GnRH- a) pituitary down- regulation. Retrospective cohort analysis. Institutional. Women undergoing 157 consecutive IVF cycles suppressed with leuprolide acetate (LA) started in the midluteal phase and stimulated with recombinant FSH. Only women <40 years of age and with a basal cycle day 3 serum FSH ≤ 9 IU/L were included. Serum LH levels were measured on cycle days 3 (D3) and 10 (D10). Delivery rates. Other secondary outcome measures included fertilization rate, clinical pregnancy rate, and parameters of ovarian response (peak E2, number of metaphase II oocytes, and number of ampules of recombinant FSH). No significant differences were found with respect to ovarian response, fertilization rate, and outcome of pregnancy, when three threshold values of D3 and D10 serum LH (1, 1.5, and 2 mIU/mL) were analyzed. In addition, no significant differences were found between conception (n=87) and no conception (n = 71) groups with respect to D3 or D10 LH. Receiver operator characteristic (ROC) analysis showed that neither the serum LH concentration on D3 nor on D10 was able to discriminate between conception and nonconception cycles (area under the curve [AUC]ROC= 0.54, AUCROC= 0.56), or between delivered pregnancies and first trimester pregnancy loss (AUCROC= 0.53, AUCROC = 0.61). The suppressed levels of early and late follicular serum LH in women < 40 years of age with normal ovarian function desensitized with a GnRH- a and treated with recombinant FSH are not predictive of ovarian response, pregnancy, or delivery. These data do not support the use of exogenous LH supplementation in this clinical scenario. To assess the value of serum LH measurements in early and late follicular phase as predictors of ovarian response and IVF outcome in patients treated with recombinant FSH with GnRH agonist (GnRH- a) pituitary down- regulation. Retrospective cohort analysis. Institutional. Women undergoing 157 consecutive IVF cycles suppressed with leuprolide acetate (LA) started in the midluteal phase and stimulated with recombinant FSH. Only women <40 years of age and with a basal cycle day 3 serum FSH ≤ 9 IU / L were included. Serum LH levels were measured Other cycle outcome measures include fertilization rate, clinical pregnancy rate, and parameters of ovarian response (peak E2, number of metaphase II oocytes, and number of ampules of recombinant FSH No significant differences were found with respect to ovarian response, fertilization rate, and outcome of pregnancy, when three threshold values ​​of D3 and D10 serum LH (1, 1.5, and 2 mIU / mL) we re analyzed. In addition, no significant differences were found between conception (n = 87) and no conception (n = 71) groups with respect to D3 or D10 LH. Receiver operator characteristic (ROC) analysis showed that neither the serum LH concentration on D3 nor on D10 was able to discriminate between conception and nonconception cycles (area under the curve [AUC] ROC = 0.54, AUCROC = 0.56), or between delivered pregnancies and first trimester pregnancy loss (AUCROC = 0.53, AUCROC = 0.61) suppressed levels of early and late follicular serum LH in women <40 years of age with normal ovarian function desensitized with a GnRH- a and treated with recombinant FSH are not predictive of ovarian response, pregnancy, or delivery. These data do not support the use of exogenous LH supplementation in this clinical scenario.