Ultrasound dating scan
Ultrasound scans are considered to be safe for you and your baby when performed by trained professionals. However, sometimes, having a scan can cause unnecessary worry. Your baby's head, limbs, hands, and feet can be seen, as well as his abdominal wall and some organs, such as his stomach. The dating scan isn't designed to look for more subtle abnormalities, though. The scan will usually show that your pregnancy is less far along than suggested by your LMP. This means that accurate dating reduces your chance of having your labour induced because your baby is thought to be overdue. It's entirely up to you whether or not you have a 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).
As long as the timings are right, you can have the NT scan and blood test at the same appointment as your dating scan. That's because the screening test needs an accurate due date to be reliable.
Hormones in your blood vary according to your stage of pregnancy.
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. However, conception doesn't actually occur until around 14 days after your LMP, or later if your cycle is longer than 28 days. Multiple pregnancy: antenatal care for twin and triplet pregnancies CG129.