During which trimester does high blood glucose significantly increase the risk of birth defects?

High blood glucose levels pose the greatest risk of causing birth defects primarily during the first trimester of pregnancy. This period is critical as it is when the major organs and structures of the fetus are developing. Elevated glucose levels during this time can interfere with normal embryonic development, leading to congenital anomalies, particularly affecting the heart, spine, and neural tube.

The first trimester spans from conception through the 12th week, which is a crucial phase for cell differentiation and organogenesis. Any disruptions, such as those caused by unchecked blood glucose levels, can have serious implications for fetal development.

In contrast, while high blood glucose can continue to pose risks throughout the second and third trimesters, the presence of established birth defects associated with glucose dysregulation is less pronounced during these later stages. Instead, issues in the later trimesters are more often related to the overall growth and management of existing conditions, rather than the emergence of new birth defects.