North American Registry of Midwives (NARM) Practice Exam

At what stage of pregnancy is maternal infection with rubella most likely to cause congenital malformations?

1. First month

2. Second month

3. Third month

4. After the first trimester

The correct answer is: First month

Maternal infection with rubella during the first month of pregnancy poses the highest risk for congenital malformations, primarily due to the timing of organogenesis. The first trimester, particularly the first four weeks, is a critical period during which the major organs and structures of the fetus are developing. If the mother contracts rubella during this time, the virus can cross the placenta and interfere with this crucial developmental process. Congenital rubella syndrome can lead to a range of serious malformations such as heart defects, cataracts, and deafness. The likelihood of these outcomes significantly declines when the infection occurs later in the pregnancy, as the critical periods for the development of various organs have already passed. Thus, the risk is highest during the very early stages of pregnancy, specifically within the first month, making this the correct answer.