Luteinizing hormone (LH) plays vital role for optimal follicular growth, maturation and is responsible for inducing ovulation, various protocols in ICSI cycles used to prevent the premature surge of luteinizing hormone. Currently, flexible GnRH antagonist protocols appears to be mostly used protocols. individualization of controlled ovarian hyper stimulation (COS) needs better timing of antagonist administration, assessing variation in LH levels during COS helps in determining appropriate initiation of inhibition .This prospective comparative observational analysis was made on one hundred twenty females with infertility who were undergoing ICSI flexible antagonist protocol at the “High Institute for Infertility Diagnosis and Assisted Reproductive Technologies/Al-Nahrain University” from October 2020 to April 2022, primary infertility was the with higher percentage (78.3%) than the secondary type. However; the main cause of infertility among the participant was male type (36.7%) fallowed by the combined one (20.8%). A highly significant difference was present in LH levels at all time points, with level decreasing from 4.99 ± 1.90 at baseline to 4.82± 2.15 at antagonist starting day to 1.63± 0.87 at trigger day and p value was > 0.001, no statistical difference in LH levels regarding the three time points between patients who get pregnant and non-pregnant women with pregnant patients having higher baseline lower antagonist starting day, and higher trigger LH levels 5.16 ± 1.87, 4.30 ± 1.72, 4.30 ± 1.72 respectively. Difference in LH level between cycle day 2 and the day of antagonist starting according to starting day of antagonist reveals that the basal LH values declined significantly (p= <0.001) until cycle day 7 of stimulation after which the basal LH start to increase and also with a high significant difference (negative values mean that the level decrease in comparison to the base line level).The comparable LH level in the current study reveals that earlier initiation of antagonist may serve no purpose and it is advisable to include the measurement of LH level to the criteria of antagonist initiation for better individualization and better outcome and to avoid un necessary earlier start of antagonist.