[Seasonal variations in the incidence of the conception of multiple pregnancies in two centuries (author's transl)].

Seasonal variations in the incidence of the conception of multiple pregnancies are compared in the same population area in two centuries. 12,617 singleton and 101 twin pregnancies from 1803 to 1852 are compared to 63,967 singleton, 473 twin and 5 triplet pregnancies from 1965 to 1970. In both groups the percentage decrease of multiple conceptions during the first three months of the year was higher than the percentage decrease of singleton conceptions. In both groups the percentage increase of multiple conceptions during the summer months was higher than the percentage increase of singleton conceptions. The question of the influence of light on the hypothalamic-pituitary centres as a cause of the variations in multiple conceptions is discussed. The incidence of multiple conceptions has decreased since the beginning of the 19th century independant of the progress in obstetrics and perinatology. The decreased rate of multiparas and especially older multiparas is suggested as the likely cause for this decrease.