Some natural and artificial factors increase the likelihood that a woman will have a multiple pregnancy. For the most part, this refers to increased likelihood of fraternal twins.

Some of the factors that are associated with multiple pregnancy include:

• Race. Black women have the highest rate of natural multiple pregnancy. Asian women have the lowest.
  
  
• Age. Older women are more likely to have a multiple pregnancy.
  
  
• Family history. Women with multiple pregnancies in their families are more likely to have a multiple pregnancy.
  
  
• Prior pregnancy. Women who have given birth four or more times are more likely to have a multiple pregnancy.
  
  
• Fertility drugs. Some of these drugs cause a woman to ovulate more than one egg a month, which increases the likelihood of multiple pregnancy. Pregnancies of triplets, quadruplets and higher orders have increased dramatically as a result of the use of fertility drugs.
  
  
• Assisted reproductive technology (ART). Measures that implant more than one embryo are more likely to produce a multiple pregnancy. These measures have also increased the number of higher order pregnancies.