The antenatal clinic has been the scene of much of the routine screening carried out by the medical profession, and much of what we know about people's reaction to routine screening has been derived from this setting. At present, few of the tests offered to pregnant women owe their existence to the new genetics. However, increasingly such tests will be possible and it is expected that a major application of the new genetics will be determining the genetic status of a fetus. This may involve new techniques such as direct sampling of fetal cells from maternal blood. In the immediate future, however, it will use the same techniques for obtaining information about the fetus as are currently used in prenatal testing (e.g. amniocentesis and chorionic villus sampling), even if subsequent laboratory techniques will be different.

In this chapter we shall describe the tests commonly used in pregnancy to detect fetal abnormality, summarise what is known of their psychosocial benefits and hazards and consider likely future developments including carrier screening for recessive disorders during pregnancy (see also Chapters 3 and 5). First, however, we shall discuss the important distinction between ‘screening’ and ‘diagnosis’.

Screening versus diagnosis

Most genetic disorders are extremely rare, of the order of one in a number of thousand pregnancies, and there are a great many of them. It would not be feasible to test every pregnancy for every known disorder, even if this were thought desirable.