My sis is allergic to everything and is pregnant. she is due jan. 31st and she gets itchy blisters on her bely?

she can only eat home made food and stuff like that. shes due the 31st and shes been getting itchy red blisters on her belly and her doctor told her not to worry. she said that lots of pregnant women get them and theyll go away a couple days after delivery. ive never heard of this though. has anyone?