Cronobiologic analysis of abortions in two related populations of teenager girls during two decades.

Study Objective: To identify and compare the time dynamics of artificial abortions in two (Czech and Slovak) ethnically, historically and socially closely related populations.

Design: Data have been taken separately for 12-15 and 16-18 year age girls from official exhaustive statistical sources and processed by advanced procedures of time series analysis.

Setting: Czech and Slovak Republics.

Participants: All girls of the given age.

Interventions: Legislative liberalization of abortions 1987.

Main Outcome Measures: Estimated starting values of relative numbers of abortions by 1971, increasing linear trends, period lengths of fluctuation, coefficients of determination and those of cross-correlation. Level of significance alpha = 0.05.

Results: The Czech figures are significantly higher than the Slovak. Thus, estimated abortion percentage (from pregnancies) for 1971 was for younger Czech girls 53%, and for those from Slovakia 29%. All estimated trends were increasing significantly in all cases for the Czech population (by 1.5% per year in the younger group) and in one case for Slovakia. The estimated period lengths were usually 10-12 years. Czech and Slovak data display significant positive mutual cross-correlation, the delay being 1-3 years in Slovak girls. Surprisingly, all data significantly cross-correlate with the geomagnetic index value Ap, acting as lead-lag, with 3-6-year delay for abortions.

Conclusions: Despite living in the same federal state--the former Czechoslovak Republic, both Czech and Slovak populations do differ in starting values and general trends of abortions in teenagers. This can be due to historical, racial and religious peculiarities as well as a more advanced process of industrialization in the western part--the Czech Republic. The latter hypothesis is corroborated by strong dynamism of changes and by the time delay in Slovakia. The periodicity exhibits a frequency resembling that known for solar motion round barycenter of solar system, for sunspots and geomagnetism.