Recurrent unexplained spontaneous miscarriage (RSM) is defined as three consecutive pregnancy loss prior to 20 weeks from the last menstrual period. 1% to 2% of women experience RSM. Treatment of URSM is a challenging issue. The currently available lines of treatment according to simplicity of use, reliability and degree of invasiveness include corticosteroids, sildenafil citrate, aspirin, heparin and immunoglobulins (besides good antenatal care), but up to now there are no prospective randomized studies, powerful enough, to determine a significant difference between these therapeutic protocols, with any of the above mentioned pharmacological agents.

Sildenafil Citrate (Viagra®), a vasodilator, is also described as an anti-inflammatory agent. While improving uterine blood flow in the proliferative phase, NO may have detrimental effects at the level of the endometrium during the implantation window. The NO- mediated release of cytokines such as tumour necrosis factor- from activated natural killer cells has been implicated as a cause of implantation failure.

Based on these observations, this study attempts was made to study uterine arteries and sub-endometrial blood flow during the luteal phase in normal fertile women and in patients with Unexplained recurrent miscarriage

Inclusion Criteria:

• Age: 20-35 years.
• BMI (20-30)
• History of three or more successive unexplained recurrent miscarriage.
• Normal uterine cavity by hystrography or hysteroscopy.
• No luteal phase defects by progesterone > 10 ng.
• Normal thyroid function (TSH, T3, T4)
• Normal lupus anticoagulant measured by activated partial throbmoplastine time (32-43 seconds).
• Normal anticardolipin (IgG < 20 gpl and IgM < 15 MPL measured by ELISA).
• Normal anti thyroid antibodies.
• Normal glucouse tolerance test.
• Normal parental karyotyping.

Exclusion Criteria:

• Age<20 or>35 year
• BMI<20 or>30
• Systemic diseases that might affect pregnancy such as diabetes or thyroid disorders or hypertension.
• History of consanguinity.
• Family history of chromosomal abnormalities (e.g. trisomy 21, trisomy 13, Turner's disease …etc.).
• History of autoimmune diseases, eg: systemic lupus.
• Congenital anomaly in uterine cavity as bicornate or septate uterus.
• Luteal phase defect and corpus luteum insufficiency.
• Uterine masses as fibroid or polyps.
• Patient with patuoles os.
• patient with antiphosphlipid syndrome.
• Cigarette smoking and alcohol.

Patients are randomized to receive either folic acid and sildenafil citrate or folic acid and placebo. Placebo tablets were same size and appearance of the sildenafil citrate tablets.