Belly heaviness and tightness in the third trimester (T3) occur due to the growing baby, increased amniotic fluid, and uterine expansion. As the baby gains weight, pressure on muscles, ligaments, and organs intensifies, leading to discomfort. Braxton Hicks contractions—practice contractions—cause intermittent tightness, while bloating and constipation from slowed digestion add to the heaviness. Hormonal changes also relax abdominal muscles, making the belly feel heavier. To ease discomfort, stay hydrated, eat fiber-rich foods, practice light exercises, and use belly support. If tightness becomes frequent or painful, consult your doctor to rule out preterm labor or other complications.