A scan maybe ordered when an abnormality is suspected on clinical grounds.
Otherwise a scan is generally booked in the first trimester to confirm pregnancy, exclude ectopic or molar pregnancies, confirm cardiac pulsation and measure the crown to rump length for dating.
If the nasal bone is visible at the scan then this will reduce the chance of your baby having Down's syndrome.
The view of the nasal bone should show three distinct lines: The first two lines, are horizontal and parallel to each other, resembling an 'equal sign'.
Charts have been developed for this purpose, but some simple rules of thumb can also be effectively used.
From 6 to 11 weeks gestational age, the fetal CRL grows at a rate of about 1 mm per day.
It is recommended that all pregnant women have a scan in the first trimester at around 12 weeks of pregnancy to confirm their dates.
If you are unsure of your period dates or have an irregular cycle, we suggest that you contact your doctor, midwife or health care provider as early as possible to arrange for a dating scan.
There is no hard and fast rule for the number of scans you should have during pregnancy.
During the examination, the fetus is seen by abdominal ultrasound.
Occasionally the view is not clear and it may be necessary to perform a vaginal scan.