Anencephaly and maternal common cold.

To study the risk of anencephaly related to common cold during pregnancy, a case-control study was made. The series comprised 393 Finnish mothers of anencephalic children and their time-area-matched controls in the period 1964 through 1982. Seventy mothers of anencephalic infants and 17 controls had reported common cold in the first trimester [adjusted odds ratio 4.5; 95% confidence interval (2.2-9.1)]. Reported common cold in the second trimester was not associated with anencephaly. As suggested by our previous cohort study in the same population, a true viral influenza resembling "common cold" might not explain the observed association.