There is still no clear understanding of what causes the great majority
of human congenital malformations. And since in most sorts of human
disease and pathology that yet prevail prevention usually awaits
understanding of cause, it is generally thought that the same is true of
developmental aberrations. But is this true? For the relatively few
congenital malformations whose causes are primarily environmental, it is
plain that their discovery has enabled prevention, but not nec- essarily
immediately. It took a generation from the time of the discovery that
maternal rubella was teratogenic to learn how to immunize against it.
Much debate occurred before it was appreciated that thalidomide was a
teratogen, and only its removal from the pharmacist's shelf and the end
of the epidemic of limb defects attributed to the drug overcame the last
doubts. For other proven environmental teratogens doubts and
difficulties still con- tinue. The claimed prevalence of fetal genital
distortions due to female sex hor- mones may have been exaggerated. Some
potentially teratogenic therapeutic drugs, like anticoagulants,
anticonvulsants, and anticancer chemicals, are still pre- scribed
despite this danger because of their benefits to pregnant women. For
those congenital malformations whose basis is predominantly genetic or
chromosomal it is different, however. Prevention has not been achieved
by the discovery of such causes, as dramatic and revolutionary as some
of them have been, except in the questionable sense of interference with
reproduction by genetic coun- seling or prenatal elimination. But this
has not inhibited the romanticists.
