This is a detailed scan during the second trimester which is carried out in order to look for any abnormalities in the baby’s structural development and growth, to examine the fetal organs including the heart (fetal echocardiography), and to check the amount of amniotic fluid, the morphology as well as the position of the placenta. It also includes a Doppler ultrasound test of the mother’s vessels.
Using the results of both first and second trimester screening helps to assess the individual risk of chromosome abnormalities. It is, however, not possible to completely rule out any genetic abnormality such as the Down syndrome. The ideal time to perform the test is at 20 to 23 weeks. In particular cases, such as maternal adiposity or a family history of birth defects, it may be necessary to carry out this scan earlier including a transvaginal ultrasound.
Third Trimester Screening
(around the 30th week of gestation)
The third trimester is the best time for evaluating fetal growth, the quantity of amniotic fluid as well as the vessels of the mother and the baby through Doppler ultrasound, thus recognizing in time if the placenta functions properly or if there are any dangers for the baby. Especially in case of abnormal second semester screening tests, multiple pregnancy, a low level of amniotic fluid, risk of insufficient supply to the placenta, fetal infections, or incompatibility in blood type between mother and fetus, specific examinations are recommended during the third semester of pregnancy. Third trimester ultrasounds may identify organ fetal abnormalities with a late onset, such as ventricular septal defects or urinary tract malformations. The prenatal diagnosis of these malformations can supply useful information for the eventual birth in specialized centers, for the timing and type of delivery, and for an adequate natal and postnatal assistance.