my sister was pregnant and at was going to a free clinic for check ups and it was very basic care no ultrasounds and rarely had Doppler to hear the baby's heartbeat. she went into a regular doctor to try to get an ultrasound ( she should be 26 weeks pregnant, and the doctors told her that she is only 13 weeks pregnant and has a serious infection likely she had a miscarriage and did not know it and became pregnant real soon after the miscarriage. I am shocked, can you tell me how this could happen and is it rare and what kind of problems should we be watching out for with the current pregnancy aseptically when it comes to infections.