The anomaly scan (second level examination) (20 to 23 weeks)
The anomaly scan is performed between the 20th and the 24th week of the pregnancy and consists of a series of measurements to check the growth of the baby and calculate the weight, checking the position of the placenta, the volume of the amniotic fluid and examine in detail the fetal organs. The head, the brain, the face, the spine, the chest, the heart, the abdomen, the kidneys, the bladder, the arms and the legs are examined, according to a well-described protocol. This detailed examination can detect about 70% of the serious abnormalities. Alas, no ultrasound examination, however detailed and scrupulous it may be, can detect all potential problems nor can it guarantee the birth of a normal child.
The fetus is examined for signs (markers) of chromosomal abnormalities.
About half of the fetuses affected by Down syndrome have at least one of the markers, although the majority of fetuses with markers are normal. The results of the first trimester screening combined with the findings of the anomaly scan will produce the final estimation of the risk for chromosomal abnormality.
The blood flow in the uterine arteries of the mother (the big vessels that supply the womb) is examined by colour Doppler. If the resistance in those vessels is higher than usual the risk increases for the mother to develop high blood pressure and/or the baby to have low birthweight. About one in five women with high resistance in the uterine arteries will develop these complications, therefore this group needs regular blood pressure checks and monthly ultrasound scans to ensure normal fetal growth.
The measurement of the cervix of the uterus is recommended. The cervix is the lower part of the womb that normally remains closed during the pregnancy and opens during the birth. The cervix can be measured reliably by transvaginal ultrasound examination. If the cervix is very short (less than 15mm) the risk of having the baby very early (premature birth) is increased. In such cases the doctor will advise you about possible interventions in order to avoid this complication. There is evidence that with appropriate action the risk can be reduced to almost half.
