I conceived a child on April 25th, 2010. I believed that I was pregnant with twin's. Two week's after conception. My first ultrasound took place June 1st. My doctor found a large sac with a baby and a smaller sac that didn't have anything in it. I was told to come back in a week. By June 14th. I began to bleed and did so for twelve hours. My doctor told me then that the second sac was a Subchorionic Hematoma. A week later. Another ultrasound was done, and that bleed was beginning to clear. But there was still a sac that continued to grow. Finally on June 24th. Another ultrasound discovered that all the bleed was gone, and a sac of clear fluid. Amniotic fluid was left. My doctor also see what looked like a baby starting to grow. A baby around four weeks. But we couldn't see a heart beat yet. Still that sac and the baby continue to grow. My doctor has told me that it's seem's like both babies were conceived at different times. Or six week's apart. I have another ultrasound tomorrow. Where one baby should be 11w4d the other 5w4d. Have you heard of this or have any insight?

Conceiving another baby whilst already pregnant is common in some animals but rare in humans. It is called superfetation. I'm not really sure what you would like to know about it but if you Google this you will find some information.

This must all seem pretty scary. Hope you get good news about how things are going.

Edit - I've just realised what your user name actually is so I'm guessing you have already been looking at this. I presume you are hoping to find someone on here who has experienced/ come across this in the flesh. You know it's pretty rare but just maybe one of our maternity experts might have some extra insight.