What specific mechanism of action associated with juniper poses a risk during pregnancy?

Its role as a diuretic agent, which might cause uterine stimulation.

The primary concern regarding juniper consumption during pregnancy stems from its recognized function as a diuretic. Diuretics increase urine production, which, while potentially useful in non-pregnant states for flushing the system, can dangerously interfere with the delicate fluid and electrolyte balance that pregnancy already subjects to hormonal shifts affecting kidney function. More critically, some diuretics are contraindicated because they carry the risk of causing uterine stimulation, which directly threatens the continuation of the pregnancy. Therefore, the diuretic action combined with the potential for uterine stimulation makes juniper a substance advised for avoidance.