Abortion

Before considering the role spontaneous abortion plays in bringing about the level of NTD seen at birth a word or two must be said about the larger topic of abortion and malformations generally. I was once led to write that “it is astonishing…that 80% of human conceptions spontaneously perish during the course of pregnancy. Forty percent are lost before pregnancy is discovered and…wastage of clinically recognized pregnancy is double or more the 10–20% commonly reported in the past. Those absent at birth, teleologically interpreted as being mercifully sifted out, comprise a very large proportion of the accidents of nature that result in defective conceptuses. Forty to sixty percent of spontaneous abortions are chromosomally abnormal…while only 0.6% of liveborn have such abnormalities…. Forty to fifty percent of spontaneous abortions are morphologically abnormal, but by term 80% of such conceptions are eliminated and a mere 3% of births are congenitally malformed” (Kalter 1983, p ix). As was so picturesquely queried, “where have all the conceptions gone? (Roberts and Lowe 1975). Neural tube defects are thus not unique in largely being discarded before they can be born, but they are, it seems, a large fraction of the discarded.