Dating by ultrasound

By then, it's likely that the placenta will have moved away from your cervix. It is possible to count the three blood vessels (two arteries and a single vein) in the umbilical cord, but your sonographer may not do this. She will check to see that's there's enough amniotic fluid for your baby to move freely, though. Rarely, though, a condition may be so serious that a baby can't survive. If the condition is treatable, it will help the hospital team to know in advance, so they can make sure your baby has the right care as soon as he's born.

About 15 per cent of scans will be done again for one reason or another. If antenatal screening tests find a possible problem NHS Choices, Health A-Z.

The placenta will be described as low if it reaches down to or covers the neck of your womb (your cervix). uk [Accessed July 2017] Im now 21 weeks,i had my scan last Saturday, and they told me to do cardio scan again on Wednesday because of ARSA, is anyone have have xperience to ur child before, and how is it now, pls.

If the placenta is lying low in your womb, you'll have another scan in the third trimester to check its position.

The most common reason is that the sonographer has not seen everything she needs to see.

This may be because your baby is not lying in a good position, or that you are overweight, in which case the scan should be repeated at 23 weeks.