Many couples routinely use contraception in an effort to avoid unwanted pregnancies. In contrast, many other couples want to have children but find it difficult to conceive or to carry a pregnancy to term. According to the Centers for Disease Control and Prevention (CDC), more than 6 million women (1 in 10 women of childbearing age) in the United States suffer from infertility; other estimates put forward figures of up to 15% of women. A couple is considered infertile if they have participated in unprotected coitus for a year without becoming pregnant. The problem is with the woman in approximately 35% of these couples, with the man in about 35%, and with both partners in approximately 20%. In 10% of cases, the cause is unknown. A couple can also be infertile because of pregnancy wastage, or the inability to maintain a pregnancy once established.