The aim of a pregnancy ultrasonography scan is to observe the development of the unborn baby and detect any abnormalities and disorders during the pregnancy. The ultrasound is carried out either vaginally or through the abdomen. Three ultrasound scans are usually carried out in pregnancies where there are no complications.
- First trimester (10th-13th week of pregnancy): This assesses how normal and advanced the pregnancy is. It will show if the baby is of reduced size, and if patients are having a multiple pregnancy or not. Measurement of the neck skin thickness can also detect any chromosome abnormalities (Down syndrome).
- Second trimester (20th-23rd week of pregnancy): This assesses how the baby is growing and the amount of amniotic fluid. Malformations of the head, brain, spine, heart, kidneys, stomach and limbs are also visible. It will also show the position of the placenta (afterbirth), which may provide information on possible causes for bleeding in the later stages of pregnancy.
- Third semester (30th-34th week of pregnancy): This again assesses how the baby is growing and the amount of amniotic fluid. The baby's position becomes an important factor as the due date approaches. If it is in breech position, it should still turn before birth.