Generally speaking, if a couple has normal sex life, the woman has ovulation, no abnormality is found in the gynecological examination and comprehensive examination, and the semen and other examinations of the man are normal, but the couple fails to conceive for 2 years or more, it can be diagnosed as unexplained infertility. This simply means that the patient is infertile for which no cause can be found through current testing methods. The incidence of unexplained infertility varies greatly from country to country, and most of the literature in China suggests that the incidence of unexplained infertility accounts for about 10-20% of infertility. In fact, the vast majority of unexplained infertility has a cause, which has not yet been elucidated due to the fact that many aspects of the human reproductive process are not yet fully understood. However, it is mostly believed that it may be related to the following factors: (1) undiscovered reproductive defects: in recent years, the rapid development of fertility technology, the diagnosis of infertility is more in-depth, such as sperm acrosome reaction examination, zona pellucida penetration test, the application of tuboscopy, etc., are an important means of in-depth understanding of the reproductive function, so that people have discovered some previously unrecognized reproductive defects. However, these diagnostic methods are not yet clinically practical and the results are not absolutely reliable. (2) Age factors: the incidence of unexplained infertility increases when a woman’s age is >30 years old, and the incidence of unexplained infertility increases when a woman is over 35 years old, especially when she is over 40 years old, the rate of chromosomal abnormalities increases, and the ovarian reserve decreases, which is manifested in the decline of the ovarian endocrine function and the quality of the eggs, and although all the tests are normal, the natural fertility has significantly decreased and unexplained infertility occurs. (3) Luteal insufficiency: although there is ovulation, but the luteal insufficiency, progesterone secretion is insufficient, so that the endometrium secretion is not good, not conducive to the fertilization of the egg, resulting in the occurrence of unexplained infertility. (4) Pelvic mild endometriosis, mild endometriosis is often no obvious symptoms, but abnormal immune function, increased macrophage activity in the peritoneal fluid as well as elevated levels of prostaglandins, easy to cause infertility. (5) cervical mucus factors, cervical mucus physical and chemical properties of the changes can directly affect the survival of sperm vitality and penetration ability. (6) endometrial factors: the endometrium of the uterus poor response to estrogen, ovulation endometrial thin, not conducive to the fertilization of the egg bed. (7) Mental and psychological factors: mental tension and unstable psychological factors can affect the function of hypothalamic-pituitary-ovarian gonadal axis, thus affecting menstruation and ovulation. Unexplained infertility is a common and challenging diagnosis for both patients and clinicians. Once diagnosed with unexplained infertility, most patients believe that without a clear cause of infertility there may be no effective treatment. The truth is that most of these patients can conceive with treatment. Unexplained infertility untreated monthly natural conception rate of about 1-3%, scholars at home and abroad proposed that the treatment should follow the first simple, inexpensive treatment to start, such as ineffective, then the complex, expensive assisted reproductive technology. That is, the first step: the application of clomiphene to promote ovulation and ovulation monitoring and guidance of coitus treatment for 4 cycles; that is, the first outpatient ovulation monitoring or simple ovulation, which is applicable to infertility for a short period of time and the ovarian function of the patient is still possible. If necessary, artificial insemination treatment can be added. Step 2: Ovulation promotion (HMG) + intrauterine insemination treatment for 3 cycles; i.e. formal ovulation promotion and monitoring of ovulation, as well as artificial insemination during ovulation. Step 3: In vitro fertilization – embryo transfer (IVF). If there is no pregnancy after more than 3 cycles of artificial insemination, it is considered that increasing the number of artificial insemination again will not improve the pregnancy rate, so it should be transferred to IVF treatment in time. There is a large amount of data confirming that ovulation induction + sperm optimization + uterine insemination is one of the effective methods of treating unexplained infertility. To summarize: if you have not been pregnant for many years after marriage and the cause of infertility has not been found, it is recommended to follow the principles of unexplained infertility treatment as early as possible. So as not to delay the best time for treatment.