Secondary infertility is when a woman has been pregnant before but has not conceived after a year of not using contraception. The causes of secondary infertility are divided into male factors and female factors. Common male infertility factors include older age or habitual smoking and drinking, leading to decreased sperm quality. Female infertility factors are more numerous, such as excessive sexual activity during reproductive years or weak immune system leading to pelvic inflammatory disease. This inflammation can affect the fallopian tubes, causing blockages and resulting in infertility due to tubal factors; it can also spread to the endometrium, causing endometritis and altering the intrauterine environment, making conception difficult. Some women may suffer from endometriosis, which can also lead to infertility. In some cases, women who have had uterine procedures may experience adhesions in the cervical canal and uterine cavity or abnormal uterine shapes, leading to infertility. Additionally, some women experience significant blood loss after childbirth, leading to pituitary necrosis, hormonal imbalances, and ovulation disorders, which can affect normal conception.