A normal pregnancy in a normal couple requires the following basic elements: 1. A normal egg (from the woman) and a normal sperm (from the man). A normal woman typically expels one to two eggs in a menstrual cycle, while a normal man can release 200-300 million sperm in a single ejaculation. 2. Normal reproductive ducts. The female internal reproductive system consists of the vagina, uterus, and both adnexa (ovaries and fallopian tubes). The male reproductive system consists of reproductive glands (testes), transport ducts (epididymis, vas deferens, ejaculatory ducts, male urethra) and accessory glands (seminal vesicle glands, prostate glands, urethral bulbous glands). 3. Sperm and egg can combine normally (fertilization). 4, endometrial tolerance, that is, the development of the endometrium should be synchronized with the development of the embryo, and can accept the embryo. After intercourse, the sperm passes through the vagina and reaches the uterine cavity, the potbelly of the fallopian tube, and after the ovary discharges the egg, the umbilical end of the fallopian tube grabs the egg like a hand and transports it to the potbelly of the fallopian tube to wait for the sperm. After the sperm and egg are fertilized and turn into an embryo, the fallopian tube transports the embryo to the uterine cavity, where it will be deposited and develop. A mistake at any of these points will affect the process of pregnancy and result in infertility.