The cause of infertility may be in the female, male or both sexes. The female factor is about 60%, the male factor is about 30%, and the mutual factor is about 10%. Female infertility factors (1) Vulvar and vaginal factors: ① Abnormal development of vulva and vagina: hermaphroditism includes true hermaphroditism and pseudohermaphroditism, the latter such as testicular feminization, congenital adrenal cortical hyperplasia, ovarian masculinization, etc. Abnormal hymen development: hymenal atresia, hard hymen, etc. Abnormal vaginal development: congenital complete or partial vaginal atresia, double vagina or vaginal septum. ② scar stenosis: vaginal injury forms adhesive scar stenosis, which affects sperm entry into the cervix and affects fertilization. (3) Vaginal inflammation: mainly trichomonas vaginitis and fungal vaginitis, which do not affect fertilization in mild cases, but in severe cases a large number of leukocytes consume the energy material present in the semen, reduce sperm activity, shorten survival time, and even phagocytose sperm and affect insemination. (2) Cervical factors: the cervix is the way for sperm to enter the uterine cavity, and the amount and nature of cervical mucus can affect whether sperm can enter the uterine cavity. (1) Abnormal development of the cervix: congenital cervical stenosis or atresia, poor elimination of menstrual blood, reduced menstrual flow, dysmenorrhea and possible complications of endometriosis in mild cases. The cervical canal is dysplastic and slender, which affects the passage of sperm; the mucous membrane of the cervical canal is underdeveloped then the glandular secretion is insufficient. ②Cervical inflammation: In severe cases, the purulent leucorrhea in the cervical canal is increased and sticky, which affects sperm penetration. (3) Cervical redundancy: cervical polyps, cervical fibroids, etc. block the cervical canal to affect fertilization. (3) uterine factors: ① congenital malformation of the uterus: abnormal uterine development such as congenital uterine agenesis, stumpy uterus, bicornuate uterus, longitudinal uterus, etc. all affect conception. ②Endometrial abnormalities: endometritis, endometrial tuberculosis, endometrial polyps, endometrial adhesions or poor endometrial secretion response affect the fertilization of eggs. (3) Uterine tumors: endometrial cancer causes infertility, most patients with endometrial atypical hyperplasia are infertile, uterine fibroids can affect conception, and submucosal fibroids can cause infertility or miscarriage after pregnancy. (4) Fallopian tube factors: The fallopian tube has the function of transporting sperm, collecting eggs and transporting fertilized eggs to the uterine cavity. Tubal pathology is the most common factor in infertility and any factor that affects the function of the fallopian tubes can affect fertilization. (1) Tubal insufficiency: tubal dysplasia affects peristalsis, which is not conducive to transporting sperm, eggs and fertilized eggs, making it easy for tubal pregnancy to occur; congenital over-elongation and distortion of the fallopian tubes affects the movement of sperm or eggs. Tubal inflammation: Tubal inflammation can cause adhesions at the umbilical end or obstruction of the lumen, and adhesions between the fallopian tubes and surrounding tissues affect peristalsis and infertility. Tubal tuberculosis causes tubal stiffness, fistula, etc. (3) Peri-fallopian tube lesions: endometriosis is more common. Ectopic endometrium forms nodules in the fallopian tubes or ectopic endometrium outside the pelvis causing tubal adhesions. (5) Ovarian factors: ① abnormal ovarian development: polycystic ovaries, undeveloped ovaries and ovarian insufficiency. (2) Endometriosis: The traditional view is that endometriosis is the external growth of the endometrium beyond the uterine cavity (excluding the myometrium). When the endometrial tissue with growth function appears in other parts of the body than the mucosa covering the uterine cavity, it is called endometriosis. The relationship between endometriosis and infertility was reported in Tianjin and Shanghai, where primary infertility accounted for 41.5% to 43.3% and secondary infertility 46.6% to 47.3% of patients with endometriosis, while the infertility rate of normal population was 15%. Severe endometriosis causes adhesions that affect ovarian function and prevent the maturation and release of oocytes. (3) Luteinized unruptured follicle syndrome (LUFS): Brosen hypothesized that LUFS is one of the causative factors of endometriosis, based on the fact that in LUFS, 17-beta estradiol and progesterone are less in the ascites than normal because of unruptured follicles, and the loss of inhibition of ectopic endometrial cells. The patient’s ovaries are not ovulating. (4) Luteal insufficiency: Insufficient luteal phase secretion in ectopic patients affects conception. (5) Ovarian tumor. (6) Ovulation disorders: all factors that cause ovarian dysfunction leading to non-ovulation can lead to infertility. (1) Central influence: Hypothalamic-pituitary-ovarian dysfunctional axis disorder, causing menstrual disorders such as anovulatory menstruation and amenorrhea; pituitary tumor causing ovarian dysfunction and infertility; mental factors such as excessive stress and anxiety can affect hypothalamic-pituitary-ovarian axis and inhibit ovulation. (2) Systemic diseases: severe malnutrition, excessive obesity or lack of certain vitamins in the diet, especially E, A and B, can affect ovarian function; endocrine metabolic diseases such as hyper- or hypothyroidism, hyper- or hypoadrenocorticism, and severe diabetes can also affect ovarian function and lead to infertility. Local ovarian factors: congenital ovarian insufficiency, polycystic ovary syndrome, premature ovarian failure, functional ovarian tumors such as granulosa-follicular membrane cell tumors, testicularoblastoma, etc. can affect ovarian ovulation; ovarian endometriosis not only destroys ovarian tissue, but can also cause severe pelvic tissue adhesions and cause infertility. 2, male infertility factors are mainly sperm production and sperm transmission disorders. External genital and semen examination should be performed to clarify whether there are abnormalities. (1) Semen abnormalities: such as no sperm or low sperm count, reduced vitality, abnormal morphology. Factors affecting sperm production include: ① congenital developmental abnormalities: congenital testicular hypoplasia cannot produce sperm; bilateral cryptorchidism leads to atrophy of the varicocele and other factors that prevent sperm production. ② Systemic factors: chronic wasting diseases, such as long-term malnutrition, chronic poisoning (smoking, alcoholism), and excessive mental stress may affect sperm production. (③Local causes: mumps complicating orchitis leading to testicular atrophy; testicular tuberculosis destroying testicular tissue; varicocele sometimes affecting sperm quality. (2) Obstructed sperm transport: tuberculosis of the epididymis and vas deferens can block the vas deferens and prevent sperm from passing; impotence and premature ejaculation cannot allow sperm to enter the female vagina. (3) Immune factors: sperm and sperm plasma produce antibodies against their own sperm in the body can cause male infertility, and ejaculated sperm can not pass through the cervical mucus because of their own agglutination. (4) Endocrine dysfunction: male endocrine is regulated by the hypothalamic-pituitary-testicular axis. Pituitary, thyroid and adrenal gland dysfunction may affect the production of sperm and cause infertility. (5) Sexual function abnormalities: dysplasia of external genitalia or impotence leading to difficulty in sexual intercourse, etc. 3. Factors of both sexes (1) Lack of basic knowledge of sexual life. (2) Excessive mental tension caused by the eagerness of both men and women to have children. (3) Immunological factors: recent studies on immunological factors have concluded that there are two kinds of immunological conditions that affect conception. (1) Alloimmunity: sperm, seminal plasma or fertilized eggs are antigenic substances that are absorbed by the vagina and endometrium and produce antibody substances through immune reactions, so that sperm and eggs cannot combine or fertilized eggs cannot be fertilized. Autoimmunity: It is believed that the presence of autoantibodies to the zona pellucida in the serum of infertile women can prevent sperm from penetrating the egg after reacting with the zona pellucida, thus preventing fertilization. 4. Factors affecting conception The general factors affecting conception are the exclusion of abnormal development of the reproductive system or organic lesions of the reproductive system that affect fertility, and the following factors can affect conception. (1) Age: The most fertile age for men is 24 to 25 years old and for women is 21 to 24 years old. According to some scholars, there is no significant difference in fertility between men and women before the age of 35, while their fertility gradually decreases after the age of 35, and the incidence of infertility can rise to 31.8%, and up to 70% after the age of 40, while there are few pregnancies after the age of 45. (2) Nutrition: Nutrition is closely related to reproductive function. According to the literature, women with severe malnutrition after marriage, anemia, wasting and living in economically deprived areas have lower fertility or are infertile. Yet the other extreme is overnutrition, that is, excessive obesity, can also cause hypogonadism, leading to infertility or reduced fertility. (3) trace elements and vitamins: In recent years, many domestic and foreign scholars have noticed that trace elements, namely zinc, manganese, selenium, copper and other elements, as well as vitamins E, A, C, B12, etc., are closely related to the sexual function of men and women, the secretion of sex hormones, these trace elements and vitamins play an important role in maintaining the function of human reproductive endocrine and the coordination of hypothalamic-pituitary-gonadal axis function. If there is a serious deficiency of trace elements or even vitamin deficiency, it can also reduce the ability to conceive or cause infertility. (4) Psychological factors: Some scholars have found that excessive mental tension or excessive anxiety and anxiety cause emotional disorders and various psychological disorders in women, which subsequently affect the endocrine balance between hypothalamus-pituitary-ovary through the neuroendocrine system, leading to non-ovulation and amenorrhea and infertility. (5) Other aspects: The presence of bad habits can also affect the fertility of both men and women, such as long-term smoking, alcoholism or exposure to narcotic drugs and toxic substances, which also have a negative impact on the fertility of men and women, as well as environmental and occupational pollution, such as noise, chemical dyes, mercury, lead and cadmium, which can also affect the fertility of women.