A 24-year-old primigravida from Delhi presents to the antenatal clinic at 16 weeks of gestation (by last menstrual period). Transabdominal ultrasound is performed for routine anomaly screening. The sonographer notes a midline defect in the anterior abdominal wall with herniation of bowel loops and liver into the amniotic sac, with no covering membrane. The defect measures approximately 5 cm. What is the most likely diagnosis?