During her lifetime, a woman will expel about 400 eggs, 1-2 eggs per month, in most cases 1 egg, and alternating between the two ovaries. A mature egg is capable of conception and if it unites with sperm to form a fertilized egg, pregnancy will result. In the case of a single egg, most of the pregnancies are single, while a few may become twin in the middle of the fertilization process. If two eggs are expelled, the probability of conceiving twins increases significantly. However, some women need to take ovulation medication because of poor ovarian function. The ovulation medication will cause the ovaries to expel more than one egg within a month, which will increase the probability of twins, and is only suitable for women with ovulation disorders.