Which condition is also an absolute contraindication to exercise in pregnancy?

Cervical insufficiency is considered an absolute contraindication to exercise during pregnancy because it poses a significant risk of premature birth or miscarriage. This condition involves the cervix being weak and unable to stay closed, potentially leading to early labor or the inability to carry a pregnancy to term. Engaging in physical activity can increase the risk of complications, making it critical to avoid exercises that could exacerbate the condition.

While the other options present important considerations for the health of both the mother and the fetus, they are not classified as absolute contraindications to exercise. Symptomatic severe eating disorders, chronic undernutrition, and untreated thyroid disease can all have negative effects on pregnancy and maternal health, but with proper medical management, exercise may still be appropriate in these cases under careful supervision by a healthcare provider. Therefore, cervical insufficiency stands out as a specific situation where exercise can directly threaten the outcome of the pregnancy.