Because it was early for the heartbeats, they are doing another ultrasound in 2 weeks to check again. I went to the drs office at 4 wks pregnant & we couldnt see a sac but we did see the my left ovary released 2 eggs! i went back 2 wks later(6 wks pregnant) and we were able to see 2 sacs and 2 beating hearts!

The heartbeats didn't show up until the following week!

I had an ultrasound last week and they saw one sac and a implantational bleed. Yesterday, bleed is gone and revelealed a 2nd sac, fetal pole, and 2 heartbeats.

Rescanning in a week or two may reveal a second heartbeat, or the scan may show that one sac is growing and the other still empty.

It is fairly common for twins to be conceived but for only one to grow and develop. If you're pregnant as a result of a fertility treatment such as in vitro fertilisation (IVF), you'll probably have an ultrasound as early as four or five weeks into your pregnancy.

Any discordancy in nuchal translucency, however, can also be due to an increased risk of development of Twin to Twin Transfusion Syndrome (40% PPV – positive predictive value) or due to other structural abnormality.

If you are diagnosed with carrying monochorionic (MC) twins, whether diamniotic or monoamniotic, you will be classed as having a high-risk pregnancy.

You could be, although the most common reason for a bigger than expected bump is that your conception date isn't what you thought it was.

If you're measuring large, you can request a dating scan which will determine whether your estimated due date is correct and whether you really are carrying twins.

At these times the membrane is usually easier to see.