Sheri is pregnant for the first time. Her cousin visited her yesterday. She told Sheri that her neighbour had delivered a baby with a birth defect. Like all mothers-to-be, Sheri is very concerned and wants to know how she can find out if her baby is normal.

For decades, all that an obstetrician could monitor were the external manifestations of pregnancy. It was only in the seventies, with the advent of ultrasound scanning, that we could actually unravel the physical mysteries of the unborn baby. Ultrasound scanning is a test in which sound waves are changed to images which enable us to examine internal structures. Ultrasound scanning allows us to observe the baby from the very early stages of pregnancy and look for various signs which can reassure us of the health of the baby or warn us of impending problems. The late 20^th century therefore saw the emergence of a gateway to the womb, giving us a glimpse into the hitherto hidden world of the fetus.

Tests for birth defects

Some tests for birth defects are offered to all pregnant women. Others may be offered if the medical history, family history, or physical exam raises a question about the baby's health. Tests do not look for all birth defects that could occur.

Tests also are not 100% accurate. The fetus could have a birth defect even if testing does not show a problem. This is known as a false-negative result. Also, a test result could be positive even though the baby is healthy (false-positive test). Your obstetrician or a trained genetic counsel or can explain what the test results mean.

Ultrasound scanning

The two most important times that an ultrasound should be done are at 11-14 weeks and at 20-22 weeks.  

An ultrasound exam at 11-14 weeks is important because it

• confirms the age of the fetus
• confirms the presence of one or more fetuses
• confirms that the fetus has a heart beat
• checks the nuchal translucency which is an important indicator of certain fetal abnormalities

An ultrasound at 20-22 weeks is important because it

• checks the formation of the organs of the fetus and detects birth defects
• confirms that the fetus is growing well

Even in the best of hands, some birth defects may not be detected by ultrasound and may be found only at the time of birth or even some time later.