In these days of commonplace contraception and the prolongation of higher education, adolescent pregnancies appear as a challenge to the socially-prescribed reproductive period and generally give rise to worry and incomprehension. The object of this article is to show how scientific discourse helps to reinforce the socially required age of first pregnancy. Contrary to a medicalized and normative literature, this article will also, on the basis of field studies, call into question some received ideas on the subject, and outline some other explanations for these « culturally » precocious pregnancies.