In the first trimester, your baby is measured from head to bottom. The CRL is very accurate in the first trimester, but after 13 weeks your baby can curl up and stretch out, so measuring the length becomes more difficult.
The width of the head (biparietal diameter or BPD) then becomes the best way to measure your baby.
Usually two scans are done during the first trimester.
A dating and viability scan, between six and nine weeks and an early morphology scan or NT scan between 11 and 13 weeks.
At six weeks (four weeks after conception) The yolk sac may be seen as a small white circle in the gestation sac.
Between 11 and 13 weeks, and preferably at 12 weeks, you will probably have a nuchal translucency scan.
If you are having a transvaginal scan (TVS), you will need to empty your bladder first. You will need to undress from the waist down so that the probe can be easily inserted into your vagina.
The nurse or assisting staff will usually cover your legs with a sheet while the scan is happening.
Because you're at the beginning of your pregnancy, your baby is still very small and your uterus is still lying low in your abdomen.
You will need to expose your tummy for an abdominal scan.