Finding out about having twins early in pregnancy also gives you more time to prepare for the birth and for your doctor and midwife to plan your care. Nearly all scans after 10 weeks can be done through your tummy, and most units ask you to arrive with a full bladder.
However, sometimes, having a scan can cause unnecessary worry. It won't hurt, although you may feel a little pressure on your tummy. If your womb (uterus) is very deep in your pelvis, or if you're overweight, you may be offered a vaginal scan, which can get a closer view of your baby. Most units offer a screening test for Down's syndrome and other conditions at the same time as the dating scan. Screening for Down's syndrome involves a nuchal translucency (NT) scan plus a blood test. You can have the combined screening test from 11 weeks to 13 weeks plus six days, or when your baby's CRL is 45mm (1.8in) to 84mm (3.3in).