If you've always dreamed of having a big family, the thought of having twins might be appealing. But your chance of having twins is pretty low. Still, several factors, such as your age and ethnicity as well as the use of fertility treatments, can increase your odds of having twins.
Fraternal twins are conceived when two eggs are fertilized by different sperm cells in the same menstrual cycle. They are twice as common as identical twins, which are conceived when one egg is fertilized by one sperm cell. The fertilized egg splits into two, forming two embryos in the uterus.
Fertility treatments raise your chances of having both fraternal and identical twins, but there are several other factors, like your age, race, and family history, that can increase your probability of having twins:
. Heredity: If you're a twin, or if there are twins in your family, you're slightly more likely to have a set yourself.
. Age: The older you are, the higher your chances of having fraternal twins or higher order multiples. One theory is women age 35 or older produce more follicle-stimulating hormone (FSH) than younger women. FSH is also the hormone that causes an egg to mature in preparation for ovulation each month, and women with extra FSH may release more than one egg in a single cycle. So older women are statistically less likely to get pregnant, but they're more likely to have twins if they do.
. History of twins: Once you have a set of fraternal twins, you're twice as likely to have another set in future pregnancies.
. Number of pregnancies: The more pregnancies you've had, the greater your chances of having twins.
. Race: Twins are more common than average among white and African American people and less common among Hispanic and Asian people.
. Body type: Fraternal twins are more common in large and tall women than in small women.
Certain treatments for infertility may increase the likelihood you'll become pregnant with twins, triplets, and higher-order multiples because they boost ovulation.
For example, gonadotropins are injectable fertility medications that stimulate your ovaries to produce multiple eggs during ovulation. If more eggs are released, that increases the likelihood that more than one egg will become fertilized, hence a multiple pregnancy.
Using assisted reproductive technology (ART), such as IVF, boosts your chances of having twins, but you can prevent a multiple pregnancy by asking your doctor to transfer only one embryo at a time.
According to preliminary 2019 national data, the percentage of IVF treatments that resulted in twin births after all embryo transfers are as follows:
. 7.3 percent in women younger than 35
. 6.9 percent in women age 35 to 37
. 6.8 percent in women age 38 to 40
. 5.1 percent in women age 41 to 42
. 5.9 percent in women age 43 and above