The uterus is a hollow, muscular, pear-shaped organ situated in the true pelvis. During pregnancy, it undergoes remarkable changes in size, shape, consistency, position, wall structure, vascularity and function to accommodate the growing fetus and prepare for labour and delivery. 1. Increase in size and weight: The most obvious change is enlargement of the uterus. In the non-pregnant state, the uterus weighs approximately 50–60 g, has a length of about 7–8 cm, and is approximately 5 cm wide. At term, its weight increases to about 900–1000 g, its length becomes approximately 30–35 cm, and its capacity increases enormously from about 5–10 mL to several litres. This enlargement occurs because of hypertrophy and hyperplasia of the uterine muscle fibres, increased connective tissue and increased blood vessels. During the first few weeks, uterine enlargement is mainly due to increased vascularity and hypertrophy of the uterine muscle. Later, the growing fetus, placenta and amniotic fluid contribute significantly to uterine distension. 2. Change in shape: The non-pregnant uterus is pear-shaped and flattened from front to back. During early pregnancy, it becomes more rounded or globular. By approximately 12 weeks, the uterus becomes more spherical and begins to rise out of the pelvis. As pregnancy advances, it becomes ovoid and elongated because of the increasing size of the fetus. The uterine cavity expands considerably. The walls become stretched, especially during the later months. At term, the uterus occupies most of the abdominal cavity and extends from the pelvis to the upper abdomen. 3. Change in position: In the non-pregnant state, the uterus is normally anteverted and anteflexed. During the early months of pregnancy, it remains within the pelvic cavity. Around the 12th week, the enlarged uterus rises above the pelvic brim and becomes an abdominal organ. At about 20 weeks, the fundus reaches the level of the umbilicus. Thereafter, the fundal height continues to increase until approximately 36 weeks, when the fundus reaches close to the xiphisternum. Near term, the fundus may descend slightly because of engagement of the presenting part and formation of the lower uterine segment. 4. Change in consistency: The uterus becomes soft during early pregnancy. This is associated with increased vascularity, oedema and changes in the uterine muscle. Softening of the uterus is one of the early signs of pregnancy. As pregnancy advances, the uterine wall becomes progressively stretched. The uterine muscle remains capable of contracting. During pregnancy, irregular, usually painless contractions known as Braxton Hicks contractions may occur. These contractions become more noticeable toward the end of pregnancy and help prepare the uterus for labour. 5. Changes in the uterine wall: The myometrium undergoes marked hypertrophy and some hyperplasia during pregnancy. Individual muscle fibres become greatly enlarged and elongated. The arrangement of muscle fibres also becomes functionally important for labour. During pregnancy, the uterine wall is relatively thick in the earlier months. As the uterus enlarges, the wall becomes progressively thinner, particularly near term. The upper uterine