Diagnosis of unexplained infertility is made after the recommended testing fails to reveal any abnormality. The treatment for unexplained infertility is empiric because it does not address a specific defect or functional impairment. The principal treatments for unexplained infertility include expectant observation with timed intercourse and lifestyle changes, clomiphene citrate and intrauterine insemination (IUI), controlled ovarian hyperstimulation (COH) with IUI, and IVF).

Clomiphene citrate has been widely used alone, and in combination with intrauterine insemination (IUI), for treatment of unexplained subfertility, The mechanism of action is based on its mixed estrogenic and antiestrogenic properties. Clomiphene is frequently used to treat unexplained female infertility by inducing multifollicular response and correcting potential subtle ovulatory dysfunction .,)The American Society for Reproductive Medicine,2003).

The use of clomiphene citrate decreases the uterine blood flow during the early luteal phase, a periimplantation stage., )The American College of Obstetricians and Gynecologists,1995).

Although ovulation is found in 80% of women with a cumulative effect in 6-8 months, the pregnancy rate can still be very low in these women . The possible causes are the anti-estrogenic effects of CC at the endometrium and cervical mucus level . The endometrial effect is without doubt one of the most important handicaps in infertility treatment. The pregnancy rate can be very low, especially if the endometrial thickness (ET) is <6-8 mm ., )J Turk Ger Gynecol Assoc. ,2012).

Ethinyl E2 reverse the deleterious effect of CC on endometrial development during the follicular phase. Endometrial thickness was dependent on peak E2 concentrations in serum.,(Richard P. Dickey, et.al.,2003).

Sildenafil citrate could lead to an improvement in uterine blood flow and, in conjunction with estrogen, led to the estrogen-induced proliferation of the endometrial lining .

Sildenafil citrate enhances uterine blood flow and increases endometrial thickening . The achieved implantation depends on the blastocyst's ability to infiltrate the endometrium and develop a sustaining blood supply, which requires the following genes to produce the necessary proteins for digesting the endometrial cellular matrix, to regulate cell growth, and to induce angiogenesis (Razieh Dehghani Firouzabadi,et.al.,2013).

Inclusion Criteria:

• Women whose infertility tests were normal then diagnosed as unexplained infertility.

Exclusion Criteria:

• Any cause of infertility male factor, tubal or ovarian.
• Chronic illness as cardiac or renal disease
• Any contraindication for used drugs

female unexplained infertility patients

Double blind randomisation