Pregnant women also require more protein in the second and third trimesters, according to the Physicians Committee for Responsible Medicine. Therefore, lacto-vegetarians, who consume dairy, and lacto-ovo vegetarians, who also eat eggs, may find it easier to maintain a healthy pregnancy diet than vegans.

Expectant mothers who refrain from eating meat, fish and eggs are encouraged to consume other foods rich in iron, such as leafy vegetables and grains to minimize the risk of anemia, which can lead to birth defects. Vegan and vegetarian pregnant women are also at a higher risk of becoming deficient in vitamin B-12, which is found in animal-based proteins and milk but also in certain soy products.

In 2011, Natalie Portman switched from a vegan diet to a vegetarian one while she was pregnant with son Aleph...and had cravings for cookies and cake from "regular bakeries."

This past September, Underwood was spotted giving into a non-vegan craving of her own—she was seen picked up a pint of Ben & Jerry's vanilla ice cream, which is made with cream, skim milk and egg yolks.

"I don't think I am craving anything too crazy," the singer told Yahoo! Beauty. "I try to keep it as healthy as possible and try to take care of myself. And, you know, putting good things in!"

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