1. What is one month pregnant? One month pregnant, that is, gestational age is 1 month, usually calculated from the first day of the last menstrual period. During this period, the fertilized egg has successfully implanted in the endometrium and the embryo begins to develop and take shape. 2. What behaviors should be avoided during the first month of pregnancy? During the first month of pregnancy, the embryo has not yet fully developed and is easily affected by external factors.