Ultrasound Imaging: Prenatal Testing

When Something Is Wrong

High-resolution ultrasound is usually recommended when risks of fetal defects are above normal. Such studies focus on the integrity of heart structure and the anatomy of the brain. In addition, remarkable pictures of the limbs can be obtained, including the digits. This is sometimes of importance for certain syndromes where there might be six fingers and six toes, for example. Kidney abnormalities and bladder problems can also be seen. Defects of the spine, including spina bifida, can be determined by high-resolution analysis, and defects of the long bones make a diagnosis of hereditary bone diseases possible as early as the second trimester.

On occasion, a tiny area of increased echo-density is seen in the fetal abdomen, raising an important question concerning the possibility of cystic fibrosis. Specific tests via amniocentesis may be needed to exclude this possibility. However, since routine cystic fibrosis DNA carrier tests should have been offered either before pregnancy or in the earliest weeks of pregnancy, parents should already have been recognized as carriers and at risk, and already have been offered amniocentesis for specific DNA studies if both were carriers.

Echo-dense spots may also be seen in the bowel or the heart in disorders where there is a chromosome abnormality in the fetus. While the risk in those circumstances may only be one or two percent, amniocentesis for prenatal chromosome studies is usually recommended. Noting that the nasal bone (the developing nose) is not fully developed or absent in fetal Down syndrome is proving to be an important and useful ultrasound observation.

Finally, all of the studies mentioned may be frustrated by an inability to obtain clear images. This is most frequently the case in the face of massive maternal obesity, or when there is a dramatic reduction in the amount of surrounding amniotic fluid. On occasion, clear images are not easy to obtain because of the awkward position of the fetus.

All in all, ultrasound examination of your baby in the first and second trimester can be extraordinarily valuable in screening for problems as well as diagnosing of specific fetal defects.