The doctor should be able to tell by looking at your cervix, if a full-term baby has ever passed through it. (If you had a c-section, then maybe not, unless you were dilated already when you had the c-section.) Please do tell your doctor, even if you want nobody else to know. The doctor is obliged by law to keep your confidences confidential. This would be particularly important for the doctor to know if there is a Rh-factor question involved, but in general it matters for a doctor to know the history of the person he or she is treating. If you think the doctor will not keep the confidence, change doctors.
I'm not sure if they would be able to tell, but it is something you should share with your OBGYN so they know your history and can give you the best medical care. If for some reason you don't want anyone in your family to know this you should still tell your Dr and ask them to not mention it to anyone. They won't be able to share your medical history with anyone if you don't give them permission.