The present randomized double blind study has been carried out in Gynecology and Obstetrics Department, Faculty of Medicine, Zagazig university on 70 women were previously received clomiphene citrate alone as management of infertile anovulatory PCOS women, but giving improper endometrial thickness < 7mm during the period from March 2019 to September 2019

Polycystic Ovarian Syndrome (PCOS) is the most common endocrine disorder in infertile women. Infertility affects 40% of women with PCOS. Understanding the main causes of infertility and selecting an appropriate treatment plan is a diagnostic and therapeutic priority The aim of this work was to compare the effect of Clomiphene citrate plus Estradiol Valerate versus Letrozole on endometrial thickness and pregnancy rate in infertile PCOS women underwent ovulation induction

The study was designed as a randomized double blind study using a computer-generated randomization list and sequentially numbered opaque sealed envelopes, each containing the allocation information written on a card. Envelopes were opened sequentially by a study nurse to allocate patients to the assigned group. These patients were divided into two groups:

1. Group A (clomiphene citrate & estradiol group): included 35 anovulatory PCO patients who received clomiphene citrate (Clomid; Aventis pharma S.AE, Global Napi pharmaceuticals, Cairo, Egypt) 100 mg daily from cycle day 3 to 7 with estradiol valerate 4-mg (two white tablets of cyclopregynova) from cycle day 8 to 14.
2. Group B (Letrozole group): included 35 anovulatory PCO patients who received letrozole (Femara; Novartis pharma AG, Basle, Switzerland) 5 mg daily from cycle day 3 to day 7.

Inclusion Criteria:

• patients aged 18-35 years old with complete infertility workup
• patients diagnosed as having PCOs women
• Normal semen analysis

Exclusion Criteria:

• Patients with male factor infertility, hyperprolactinemia, thyroid disorder.
• Patients with any tubal pathology or uterine pathology.
• Contraindication of ovulation induction, (Multiple ovarian cysts or allergy to inducing agent "clomid").
• Known or suspected pelvic infection (PID).