Between 11 and 14 weeks of pregnancy, a new ultrasound will be requested. This is called the nuchal translucency scan, which measures the skin fold at the back of the neck and checks for the presence of the nasal bone. This ultrasound can detect genetic issues, such as Down syndrome. If any changes or suspicions are found during the ultrasound, the obstetrician may order further tests for confirmation, such as chorionic villus sampling or amniocentesis.

As pregnancy enters the second trimester, the most detailed ultrasound is required. The morphological ultrasound is done around 20 weeks of gestation. It is usually during this scan that the baby's sex can be seen. Throughout the procedure, the baby's heart is checked, as well as brain development, the digestive system, and the baby's entire body is measured to assess growth.

During this ultrasound exam, the position of the placenta is also monitored, as it might be covering the opening of the cervix. If so, this must be followed in future ultrasounds to see if the placenta moves before the birth.

The obstetrician may request a morphological ultrasound with Doppler, which is a specialized system that can show blood flow in the uterus, the baby, and the placenta. Usually, you can tell one exam from the other because the Doppler uses red and blue to indicate blood flow. In the third trimester, ultrasound mainly serves to monitor the baby’s growth, the amount of amniotic fluid, the baby's position, as well as the degree of placenta maturation.

The purpose of ultrasound during pregnancy is to detect possible developmental, genetic, or cardiac issues, as well as to monitor the proper development of the fetus. If any problem is detected, suitable treatment can start immediately while the baby is still in the womb. If treatment cannot be provided during pregnancy, it can be planned to start at birth, so the baby has the best chances for life and care.

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