A research performed by Gary Steinman, M.D. of the Long Island Jewish Medical Center in New Hyde Park, New York reveals diary impact on twin birth risks.

Although some women find id easier to be pregnant only once and have two or more children, multiple pregnancies are risky pregnancies for both children and a mother. It may contribute to health problems in mothers like and premature delivery, and hypertension and congenital defects between children.
His study revealed that eating dairy products may be contributing to the risk of multiple pregnancies. The main suspect is a synthetic growth hormone insulin-like growth factor a.k.a IGF that is present in diary products.

Higher levels of IGF in milk were related to ovarian sensitivity influencing more eggs being released from the ovaries.
There is an increase in number of multiple pregnancies since 1975 but there may be other reasons for it like IV treatments that also increase multiple pregnancy risks.

Doctor Gary Steinman concluded in the end that women should rather have soy or organic milk as they are supposed to have lower or no IGF levels.