Your uterus is shaped like a pear that is positioned upside down in your pelvis. The top of the uterus is called the fundus. The opening of the uterus to the vagina, called the cervix, is located at the "stem end."
The wall of your uterus is a muscle that grows and stretches as your baby grows. When it is time for your baby to be born, this muscle tightens rhythmically. This is called having contractions.
When labor starts, the contractions often feel like your baby is balling up. You may also feel pain on the front of your thighs.
Some women say contractions feel like menstrual or intestinal cramps. For others, it is mostly a backache.
When your contractions are effective they thin out, or efface, the cervix. They also push your baby down against the cervix. This makes the cervix open, or dilate.
Effective contractions start at the top of the uterus and move downward. You may feel this as the contraction starting at your back and coming around to your front.
Allina Health's Patient Education Department, Beginnings: Pregnancy, Birth and Beyond, sixth edition, preg-ahc-90026, ISBN 1-931876-25-8
Allina Health's Patient Education Department experts