Seasonality of anencephalic births and pre-ovulatory overripeness ovopathy.

The total number of births and the anencephaly incidence rate in the Netherlands, in the years 1951 to 1968 (both corrected to estimate the 'conception' curves), were analyzed to find their circannual fluctuations and to see whether there was a relation between the two. The results indicate that, as predicted by the seasonal preovulatory overripeness ovopathy (SPOO-) hypothesis, anencephalics are born disproportionately more often than expected during the peak months and less often during the troughs of the total birth curve. Overripeness ovopathy as a teratogenic factor, therefore, may offer a unifying aetiological concept which can also explain other epidemiological findings concerning congenital CNS-defects. This concept may challenge the genetic theories of their causation, and offer new possibilities for 'primary' prevention.