Two groups of unexplained recurrent spontaneous abortion, each included 65 participants. scheduled randomly into; the study group received Sildenafil Citrate and Placebo group. The intervention started from day 21-23 of the cycle preceding spontaneous pregnancy and continued till the 12th-week of gestation.

The primary outcome measure was the difference in the live birth between both groups. Secondary outcome measures were the differences between both groups regard pulsatility index (PI) and resistance index (RI), a number of take-home babies, the reported side-effects of treatment and the pregnancy-related complications.

Two groups of unexplained recurrent spontaneous abortion, each included 65 participants. scheduled randomly into; the study group received Sildenafil Citrate and Placebo group. The intervention started from day 21-23 of the cycle preceding spontaneous pregnancy and continued till the 12th-week of gestation.

The primary outcome measure was the difference in the live birth between both groups. Secondary outcome measures were the differences between both groups regard PI and RI, a number of take-home babies, the reported side-effects of treatment and the pregnancy-related complications, e.g., preeclampsia and intrauterine growth restriction (|IUGR).

Inclusion Criteria:

• Unexplained recurrent spontaneous abortion.

Exclusion Criteria:

• Abnormal uterine cavity.
• Luteal phase insufficiency.
• Endocrinal disorders, e.g., thyroid diseases, hyperprolactinemia, and Diabetes Mellitus.
• Antiphospholipid syndrome.
• Inherited or acquired thrombophilia.
• Patients had renal, hepatic or cardiovascular diseases, hypertension, history of smoking, treated with vasodilators or sensitive to or developed severe side-effects with Sildenafil Citrate.