Why is my fetal sac still empty after 8 weeks?

Q: I am 9 weeks pregnant. During my 8th week, I noticed some spotting and called up the doctor who advised complete bed rest and the spotting stopped. Later I went for a scan and the report said that the sac is empty but the sac size is of 5 weeks. There is no any embryo formed. The radiologist suggested a scan after 2 weeks. Now the spotting is changed to bleeding regularly and I am still on bed rest. I am taking Gestin (progesterone) twice daily and Folic acid - 1 daily. I have a history of a missed abortion during the 8th week with embryo grown for only 5 weeks, 3 years ago. What is the future of my pregnancy?

A:All calculations in ultrasound in pregnancy are based on the presumption that most women have 28 day regular menstrual cycles. As per this calculation an embryo and its heartbeat should be evident by six weeks from the last menstrual period. Since some cycles in some women may be longer than 28 days, conception may have been at a later date and then the size of the pregnancy and the appearance of the embryo will follow a different time-table. It would be wise to repeat the ultrasound a week from the previous one to decide the fate of this pregnancy. It could go either way.