Level 1: Reasons why you cannot have sex in the early stages of pregnancy. Early pregnancy refers to the period of 1-3 months of pregnancy. At this time, the embryo is developing and is very sensitive to the external environment. Therefore, having sex during this period may cause adverse reactions, such as abdominal pain, miscarriage, etc. In addition, in the early stages of pregnancy, female hormone levels will change and mood swings may occur easily, and sexual intercourse may increase stress and anxiety. Level 2: Reasons why you cannot have sex in the second trimester of pregnancy. The second trimester of pregnancy refers to the period of 4-6 months of pregnancy. At this time, the fetus has formed and started to grow rapidly. During this period, having sex may cause problems such as uterine contractions and premature birth.