Cyclic variations in date of last menstrual period of mothers of infants with congenital malformations in South Wales, 1964-66.

Abstract

In a review article on congenital malformations and season of birth, Bailar and Gurian (1965) stated that 'seasonal cycles in births of infants with certain malformations have been demonstrated beyond any reasonable doubt'. Recently, Wehrung and Hay (1970) have referred to the ambiguity of the term 'seasonal ', and Hewitt et al. (1971) (3) secondary-in which the characteristic is associated with season because both characteristic and season are independently related to a certain time of the year (e.g., the end of the tax year; biennial rate demands; school and public holidays). An example of this type of association is the increase in deaths from road traffic accidents at Christmas and other public holidays. It is important to bear these three categories of association in mind since the temporal pattern of variables which are directly or indirectly associated may differ from that of variables which are secondarily associated. While each association could be described as showing 'cyclic' behaviour, the first two (direct and indirect causal) are likely to have a periodic function of one year's duration marked by a varying but smooth pattern which can be fitted to a simple harmonic curve (this we have called harmonic behaviour); while the third (secondary) is likely to have a periodic function of one year's duration marked by a significant change at a particular time of each year for a certain period of time (this we have called periodic non-harmonic behaviour). However, if (on inspection of each year's data) the significant change at a particular time of year (for a certain period of time) is observed for one year only (or appears but irregularly), we would describe the temporal behaviour as episodic.An investigator concerned with the prevalence of congenital malformations who takes 'seasonal' to mean only the direct and indirect categories of association might therefore reasonably consider that fitting an harmonic curve is the appropriate test for a seasonal pattern, but one who includes secondary associations in his definition of seasonal may be justified in using the simple x2 test. If useful hypotheses are to be generated in this field it may be necessary not only to avoid the use of the confusing description 'seasonal' but also to particularize the observed cyclic characteristics of the data studied.

Hypospadias - Genetics, Epidemiology and Other Possible Aetiological Influences

“…Cyclie periannual variations in the frequency of hypospadias were found in this study confirming the reports of several authors (6,9,23,24,25). Some authors referred the seasonality of hypospadias to cyclic variations in the hormone status of the mother.…”

“…The minima and maxima, however, seem to differ eonsiderably from country to country. Whereas the maximum ofbirths of children with hypospadias was found to be in April and May in this study, Roberts et al (24,25) reported the maximum in November in England, Neto et al (23) in the last trimester ofthe year in South America, Czeizel et al (9) the same for Hungary and Avelltin (6) a summer maximum in Sweden. The reasons for the differences in the appearance of maxima in different countries remain unclear.…”

CNS malformations in the kraków region. I. Birth prevalence and seasonal incidence during 1979–1981

“…This confirms findings made by many other authors [Carter, 1973;Cassady, 1969;Elwood, 1976;Fedrick, 1976;Frezal et al, 1964;Granroth et al, 1977;Halevi, 1967;Roberts et al, 1972;Wehrung et al, 19701. However, some papers show a higher incidence of malformations in winter [WHO, 19791 and in May [Imaizumi, 19741. According to Sandahl [ 19771, peak incidence for the dates of the mother's last menstrual period were found during February to April for anencephaly, and during July for spina bifida.…”

Seasonal trends in the prevalence of hypospadias: Aetiological implications

“…The most effective means to study seasonality is to perform Edwards' and Hewitt's tests independently ( 11 , 19 ). The results of Hewitt's test should be evaluated under the assumption that no prior hypothesis exists specifying the six-month period of higher expected prevalence.…”

“…Apart from the ‘specific’ tools for detecting seasonality, the use of χ 2 of heterogeneity across k time periods [e.g., 12 months of the year (k=12) in our study] could be considered. However, the power of Edwards' test is higher ( 19 ). This tool was used in the past, but has been abandoned nowadays and, if ever used, it is obligatorily supplemented by a ‘specific’ statistical tool, since the results produced cannot be unequivocally accepted; significant results do not necessarily imply a seasonal pattern, insignificant results cannot rule out a seasonal pattern.…”