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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.
The point of the scan is to work out how many weeks pregnant you are. Ectopic pregnancy and miscarriage: diagnosis and initial management CG 154.
You may have calculated the length of your pregnancy from the first day of your last menstrual period (LMP).
It may also help you to avoid feeling disappointed towards the end of your pregnancy if you think your baby is late when he's not.
The scan can check that your baby's heart is beating nicely and that he's developing normally.
Ultrasound scans are considered to be safe for you and your baby when performed by trained professionals.
You could have a dating scan without NT screening, or even change your mind on the day of your scan. 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). A blood test at what you thought was 13 weeks wouldn't be helpful if you were actually 16 weeks pregnant. It may lead to you being given a high chance for Down's syndrome, when your baby is actually developing normally (false-positive result). Addition of non-invasive test to improve screening for pregnant women.
It may show a very minor problem, or something that may get better on its own. onlinelibrary.[Accessed July 2017] Loughna P, Chitty L, Evans T et al. Fetal size and dating: charts recommended for clinical obstetric practice.