This happened to my friend, but they didn't realize she had twins. When she miscarried one, they didn't know there was a second baby. She kept waiting for her period to start TTC again, and didn't know she was pregnant. They realized when she was at 12 weeks.
ETA: I'm sorry for your loss.
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When I went in at 5 weeks there were definetely 2 sacs. Nothing inside either of them yet. I went back in at 7 weeks 5 days and there was only 1 sac and a baby. Not sure what happened to the other sac though.
Re: Vanishing Twin
This happened to my friend, but they didn't realize she had twins. When she miscarried one, they didn't know there was a second baby. She kept waiting for her period to start TTC again, and didn't know she was pregnant. They realized when she was at 12 weeks.
ETA: I'm sorry for your loss.
BFP#1: 7/14/10. EDD: 3/19/11--MMC-- D&C 9/2/10.
BFP#2: 12:22/10.EDD: 8/30/11 C/P 12/25/10
BFP#3: 10/26/11 EDD: 7/2/12-- Daniel born 7/14/12. My rainbow baby! BFP #4: 2.22/15 EDD: 11/4/15 C/P 2/28/15 BFP #5: 4/5/15 EDD 12/11/15 (Ectopic Pregnancy)
BFP #6: 3/2/16 EDD 11/5/16

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