What condition may develop in the third trimester due to increased pressure on blood vessels?

In the third trimester, increased pressure on blood vessels can lead to the development of varicose veins. This happens because the growing uterus puts pressure on the veins of the pelvic area and lower extremities, causing blood to pool and leading to dilated and tortuous veins. Varicose veins are characterized by their swollen, twisted appearance and can cause discomfort, especially during prolonged standing or sitting.

The other conditions mentioned, while serious and relevant to pregnancy, do not directly relate to the increased pressure on blood vessels in the same way. Gestational hypertension is related to elevated blood pressure during pregnancy but is not primarily caused by venous pressure from the uterus. Preeclampsia also involves elevated blood pressure and can affect the mother's organs, but it is primarily linked to placental issues rather than venous pressure alone. Placental abruption involves the premature separation of the placenta from the uterine wall, which can lead to bleeding and is not directly caused by increased pressure on blood vessels.

Thus, the development of varicose veins during the third trimester is a direct result of increased pressure on lower extremity blood vessels, making it the most relevant condition in this context.