Smokin while pregnant?

my sis is pregnant and shes been smokin the whole time she had been goin to the doctor and all seems normal but i dont think its all right. I talked to her bout it and shes like my doctor said its okay to smoke as long as im havin prenatal care. WOW THATS LAME!!! and shes due in november but what do u think! pleez tell me if im wrong here now!!!!!!!!!!!