What factors predispose couples to have twins? Here are some interesting findings.

Genetics
If you are a woman whose mother, sister, maternal aunt or maternal grandmother had fraternal twins, this trait may have been passed to you. Fraternal twins can only be conceived if a woman releases two eggs at ovulation, and this trait has been genetically predetermined in some people.

Age
If you are a woman between the ages of 35 - 39, you are more likely to conceive twins. This likelihood increases more after 40, but mostly because women are using fertility treatments at that age. Women over 35 may release more than one egg at ovulation because their cycles are being disrupted by perimenopause.

Previous Pregnancies
The more previous pregnancies and births a woman has experienced, the more likely twins will be in subsequent pregnancies. If a woman has conceived twins (especially fraternal twins) before, she is more likely to have them again.

Race/Ethnicity
In the United States, people of African descent have a higher incidence of twins than Caucasians, who have a higher rate of twinning than Asians. Native Americans have a slightly lower incidence than Asians, and Hispanics have the lowest rate of twinning.

Weight/Height
Obese women, especially those with a body mass index over 30, tend to conceive twins more often, but also have higher risk pregnancies because of the excess weight. Taller women are also more likely to conceive twins.

Diet/Nutrition
There is some scientific evidence that eating animal products, especially dairy, increases a woman's chances of conceiving twins. Vegan women who eat no dairy have a very low rate of twin conception. Women whose diets are high in folate seem to conceive twins more often, as do those who eat yams or other products high in natural estrogen-like compounds. Women in the Yoruba tribe in Africa have a phenomenal rate of twinning, and consume yams as a major part of their diet. Once twins have been conceived, consuming a healthy, adequate diet is essential for the proper development of the babies as well.

Environment
Strangely enough, some studies have found that living near a polluted area increases a woman's chances of having twins.

Breastfeeding
Women who are breastfeeding when they get pregnant again (often accidentally!) are more likely to conceive twins.

Infertility
As those who have been through the infertility process know, both infertility drugs and IVF increase a couple's chances of a multiple pregnancy.