i had a problem last year which was very tiny and the doctors told me to get it checked up after a year...however i became pregnant and when my mammogram was due i was already 6 weeks pregnant, my doctor suggested me an ultrasound instead...however...my doctor told me that any radiation or xray is always avoided strongly in pregnancy, unless if the test outweighs the potential risk...if its a life and death matter then you would go ahead and take the xray or else deferring is the best option. your doctor should tell you better though.