Baby dating scan accuracy
You may have calculated the length of your pregnancy from the first day of your last menstrual period (LMP).
This is even though you don't actually conceive until 14 days after your LMP, or later than this if your cycle is longer than 28 days.
For most mums-to-be, the first scan will be a dating scan at between 10 weeks and 13 weeks plus six days of pregnancy.
However, the timing of your first scan will also depend on how your pregnancy is going, and where you live.
If you have an irregular cycle, or if you've recently been taking the contraceptive pill, working out the date from your LMP isn't a very accurate method. The scan can check that your baby has a heartbeat and is developing normally.
Your baby's head, limbs, hands and feet, and some organs can be seen.
This measures a collection of fluid under the skin at the back of a baby's neck.
You may also be offered an early scan if you've had a previous miscarriage.Without an accurate due date, a blood test at what you thought was 13 weeks wouldn't be helpful if you were 16 weeks pregnant when the blood was taken. National Down's Syndrome Screening Programme for England.It may lead to you being given a high risk factor when your baby is actually developing normally (false positive result). Kettering: National Down's Syndrome Screening Programme Westfall RE, Benoit C. The rhetoric of "natural" in natural childbirth: childbearing women's perspectives on prolonged pregnancy and induction of labour.This is because blood tests for Down syndrome are not very accurate if you are having more than one baby.Instead, you will be offered a nuchal translucency (NT) scan.