During pregnancy the uterus grows upwards out of the woman's
pelvis. The top of the uterus (or fundus) can be felt by your caregiver feeling your belly after about 12 weeks of pregnancy. By 24 weeks of pregnancy, the myometrium muscles start stretching upwards, forming the thicker upper segment of the uterus. This leaves a thinner layer of muscle below it, known as the lower segment. The lower segment separates the cervix from the upper segment and has the role of 'taking up' or absorbing the cervix as it dilates during labour.
The muscles in the lower segment encircle the lower third of the uterus and is a relatively weaker layer of muscle with less blood supply, compared to the upper segment. This is why the cut to perform a
Caesarean operation is done in the lower segment (across the top of the pubic hairline), where it is less likely to cause excessive bleeding.
Image 1-04 and Image 1-05 illustrate the changes in shape and size that the uterus undergoes between week 6 and 16 weeks of pregnancy. They demonstrate how the muscular uterus grows with your baby.
The uterus has a natural tendency to lean slightly towards the woman's right side during later pregnancy, but is held in place by ligaments. These ligaments stretch as the uterus grows, acting like supportive anchors to stabilise it, while facilitating the baby's movements within.
Image 1-06 shows how the ligaments run from the base of the uterus to the pelvic bones, suspending the uterus.
Aches on the lower sides of the belly and temporary sharp groin pains are common during pregnancy, as these ligaments are gently strained (referred to as ligament pain), especially with sudden movements, coughing or sneezing.
Updated November 2007
Information sources
Stables D. and Rankin J. Physiology in Childbearing with Anatomy and Related Biosciences. 2004, Bailliere Tindall, Edinburgh.