Pregnancy is divided into three trimesters. In the first trimester (first 3 months), the baby’s organ development (organogenesis) has just begun, and the fetus is extremely sensitive to external factors, stress, and medications; the risk of miscarriage is high during this period, and no non-emergency treatments are performed. In the third trimester (last 3 months), the baby has grown considerably, and when the mother is sitting in a chair, the growing uterus in a supine position can put pressure on the major blood vessels (inferior vena cava), leading to sudden drops in blood pressure and fainting (supine hypotensive syndrome), as well as a risk of premature birth. The second trimester (months 4, 5, and 6) is when the baby’s organ development is complete, the mother’s hormone levels are stable, and she is physically most comfortable; therefore, fillings, extractions, and gum treatments can be performed most safely with X-ray protection (lead apron).
