HAZARDS OF THE FIRST TRIMESTER

The teratogenic hazards of pregnancy, particularly in the first trimester, were presented by Ingalls¹ in a symposium recently held under the auspices of the Ciba Foundation. The influence of the environment upon congenital malformations is not a new concept. The variety of agents and the magnitude of the impact, however, are being quantitated for the first time. These include rubella infection, hypoxia, and possibly influenza. Recounting of the critical stages of embryogenesis in the initial weeks after conception is helpful for adequate understanding of the potentialities of environmental hazards and stress. The limb buds of the embryo begin to develop in the fourth week of pregnancy. The palate begins to fuse in the sixth week. The septum of the heart emerges during the eighth week of gestation. It is not surprising to learn that a biological, a chemical, or a physical insult during any one of the chronological epochs