According to WHO:
When a women is unable to bear a child either due to the inability to become pregnant or the inability to carry a pregnancy to a live birth following either a previous pregnancy or previous ability to carry pregnancy to a live birth.

Causes:
• Anovulation, Irregular ovulation.
• Recurrent miscarriage.
• Endometriosis
• Fibroids
• Ashermann’s Syndrome.
• Intrauterine adhesion.
• Fallopian Tube blockage.
• Genital TB.
• Male factor.
• Hormonal disorders, obesity
• Endometrium problem.
• Unexplained.