According to the WebMD website, beans are a “must-eat” food for pregnant women. Packed with nutrients, they are especially rich in folate. This B-vitamin is needed for the production of red blood cells and the development of an embryo’s nervous system during the early stages of pregnancy. Even when health providers prescribe a supplement of folic acid (the synthetic form of the vitamin) during pregnancy, it’s important to eat a diet rich in natural folate. And beans are among the best sources. A half-cup serving of pinto beans provides nearly 25% of a pregnant woman’s daily need for folate.

https://www.webmd.com/baby/features/must-eat-foods-pregnancy