Which assessment finding would be most alarming for an expectant mother in her third trimester?

Sudden weight gain during the third trimester can be concerning for an expectant mother as it may indicate potential complications such as preeclampsia or gestational hypertension. Normal weight gain during pregnancy is usually gradual and should be within the guidelines provided by healthcare professionals. A significant increase in weight over a short period, especially if it is accompanied by other symptoms like elevated blood pressure or swelling, could suggest fluid retention or other serious issues that warrant immediate assessment.

While some of the other findings like intermittent back pain, mild swelling of the ankles, and frequent urination can be common and expected during pregnancy, a sudden and excessive weight gain is a deviation from normal and typically requires further evaluation to ensure the safety of both the mother and the fetus.