Why associations are not a calculator input
Some observational studies reported higher multiple-birth rates among folic-acid users or dairy consumers. People who use supplements or follow particular diets can also differ in age, pregnancy planning, healthcare access, treatment use and other factors. That makes causal interpretation difficult.
TwinCalc does not apply a diet, dairy or folic-acid multiplier. No food has been established as a safe, clinically meaningful method for intentionally conceiving twins.
Folic acid has a different purpose
Folic-acid recommendations exist to reduce the risk of neural-tube defects. They should be followed according to current local clinical guidance, not increased, reduced or skipped in response to twin-rate claims.
This evidence topic is retained to answer a common search question and to make the model exclusion explicit. It is not a nutrition plan or medical advice.