Double Vision By Bob Kurt

In very rare cases, twins become conjoined twins. Furthermore, there can be various degrees of shared environment of twins in the womb, potentially leading to pregnancy complications.
It is a common misconception that two placentas means twins are dizygotic (non-identical). But if monozygotic twins separate early enough, the arrangement of sacs and placentas in utero is indistinguishable from dizygotic twins.
A recent study has found that Insulin-like growth factor present in dairy products may increase the chance of dizygotic twinning. Specifically, the study found that vegan mothers (who exclude dairy from their diets) are one-fifth as likely to have twins as vegetarian or omnivore mothers, and concluded that "Genotypes favoring elevated IGF and diets including dairy products, especially in areas where growth hormone is given to cattle, appear to enhance the chances of multiple pregnancies due to ovarian stimulation."