Uses of the ultrasound :
Ultrasound may be used at various points during pregnancy, including:

• First trimester : ultrasound performed within the first three months of pregnancy is used to check that the embryo is developing inside the womb (rather than inside a fallopian tube, for example), confirm the number of embryos, and calculate the gestational age and the baby’s due date.
• Second trimester : ultrasound performed between weeks 18 and 20 is used to check the development of foetal structures such as the spine, limbs, brain and internal organs. The size and location of the placenta is also checked. The baby’s sex can be established, if the parents wish to know.
• Third trimester : ultrasound performed after 30 weeks is used to check that the baby is continuing to grow at a normal rate. The location of the placenta is checked to make sure it isn’t blocking the cervix.