A scan done this early will usually be done vaginally because your uterus is still deep in your pelvis in the early weeks. A vaginal scan can get closer and so is better for checking that the embryo has implanted inside the uterus. The sonographer will also note if there are any cysts in the ovaries or fibroids in the uterus.
Later in the pregnancy the scan will show more:
• It may be possible to see a small, empty pregnancy sac at about five weeks.
• At six weeks, a yolk sac can be seen and a heartbeat is visible sometimes.
• The embryo will be about 1cm long by seven weeks. The heart rate will be about 150 beats a minute.
• You should be able to make out the head, body and some movement at eight weeks. The embryo will measure 16mm.
• At nine weeks it's looking more like a baby; the head, body and limbs can be seen clearly. It's almost fully formed and is now known as a foetus.
Twins can usually be spotted at this early stage, not always. Sometimes one baby will be missed at six weeks and one heartbeat is seen, but not the other. Having a rescan in a week or two may reveal a second heartbeat. The scan may show that one sac is growing and the other is still empty. It is a fairly common event for for twins to be conceived, but for only one to develop. This is called the vanishing twin phenomenon. Scans will be able to show if the twins share a placenta.
Unfortunately, miscarriages in early pregnancy are common. If an embryo has a slower heartbeat and a small yolk sac or is growing more slowly what is normally expected, it is more likely to miscarry. The scan may show an empty sac, or a sac with a tiny embryo but no heartbeat. This is known as a missed miscarriage.