Depending on the size of the fetus, we determine the length of the pregnancy and the expected date of delivery. The number of fetuses is determined, and in the case of multiple pregnancies, whether or not each fetus has its own placenta. We assess early fetal development, viability and measure NT, which is the thickness of the fluid accumulated under the skin in the occipital or nuchal part of the fetus. The examination may also reveal important structural abnormalities of the fetus. The measured data is entered into a computer programme to calculate the risk of the three most common chromosomal abnormalities (Down syndrome or Trisomy 21, Edwards syndrome or Trisomy 18 and Patau syndrome or Trisomy 13).

Increased NT is measured in 5% increments and represents an increased risk of chromosomal and other fetal abnormalities. Since 20% of fetuses with Down syndrome and 80% of genetic syndromes do not have increased NT, DMT (free beta hCG and PAPP-A) is highly recommended in addition to the ultrasound scan, which increases the predictive value of the scan by 10% and, together with the ultrasound scan, allows 90% of chromosomal abnormalities to be detected. DMT can be performed between 8 weeks and 1 day up to 13 weeks and 6 days’ gestational length, with the maximum sensitivity at 10 weeks. Abnormal levels of the PAPP-A protein may also predict impaired fetal placental function.