First trimester ultrasonic scans may show 'soft' markers for chromosomal abnormalities, such as the absence of fetal nasal bone, an increased fetal nuchal translucency (back of the neck) to enable detection of Down syndrome fetuses.
About 18 - 20 weeks - Some women are offered a scan in the second trimester at around 18 to 20 weeks.
It is not necessary to go in very deeply, and it will not harm you or your baby in any way.
You would usually be asked to empty your bladder before vaginal scanning.
There is no hard and fast rule for the number of scans you should have during pregnancy.
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.
Ultrasound examinations are performed on your lower abdomen.
Hard tissues such as bone reflect as white in the image, and soft tissues appear grey and speckled. Examples of ultrasonography you may see used during your pregnancy.
Fluids (amniotic fluid) do not reflect any echoes so appear black. Most parents look forward to their scan because it gives them the first glimpse of their baby.
Congenital malformations, multiple pregnancies can be firmly diagnosed and dates and growth can also be assessed. Further scans may be necessary if abnormalities are suspected.28 to 40 weeks - Growth scans in the third trimester may be recommended if a previous baby was small, if you are having twins or when there are other complications of pregnancy, for instance if you are diabetic.