Doctors do not fully understand the reason why twin pregnancies sometimes occur and also, some factors can increase the likelihood of giving birth to twins, including: · The woman's age · Having a family history of twins · Having fertility treatments Conception happens when the sperm fertilizes an egg to form an embryo. However, if there are two eggs present in the womb at the time of fertilization or the fertilized egg splits into two separate embryos, a woman can become pregnant with twins. There are two types of twin: Identical twins : This type of pregnancy happens when a fertilized egg splits into two separated embryos. These embryos are monozygotic, which means that they have identical genes. Identical twins have the same sex as each other and look very alike. Non identical, or fraternal, twins: This ty...