Reproductive System: Uterus



The uterus is an organ that, prior to pregnancy, sits protected in the “bowl” of the pelvis.  It is difficult to palpate externally until you pass the first trimester of pregnancy.  Prior to pregnancy, the uterus is about the size of your fist and slowly grows to the size of… well… whatever size it needs to for your baby’s growth.

The uterus is shaped somewhat like a squash and is “hollow” to hold a growing baby and placenta.  The uterus is comprised of multiple layers (though its usually described as having only three).  The outermost layer is called the peritoneum.  Then there are three muscle layers which together, are called the myometrium.  Each muscle layer has fibers that are oriented in different directions (vertical, horizontal, and diagonal).  This allows the uterus to contract in various ways so the body can shed tissue during menses (a period), turn a baby in pregnancy and labor into an optimal position, dilate the cervix, thicken the fundus to push out a baby, expel the placenta after birth while managing blood loss, and finally to give strength so the uterus can contract to its pre-pregnancy size (an action called involution).  A complex network of actions that respond to hormones and emotions.

The innermost layer of the uterus is called the endometrium.  This layer consists of a base which is attached to the myometrium and does not shed during a period.  The part of the endometrium next to the hollow space, however, will thicken during the menstrual cycle so that a fertilized egg can implant into it for pregnancy growth.  This part sheds away during menses and during postpartum.

All these layers are only approximately 2 cm thick prior to pregnancy, and only 1 cm thick during a full-term pregnancy, but they are very powerful.  The fundus (the top part of the uterus) and the cervix (the opening at the bottom) are thicker.  There really aren’t separate parts of the uterus, the cells just change shape to accommodate the various functions needed throughout the whole reproductive cycle.  During labor, contractions move the muscle fibers, causing the fundus to get very thick to push out the baby, as the cervix gets very thin to move out of the way of baby’s passage.

At ovulation, the opening of the cervix (called the “os”) slightly softens (as much as your earlobe) and slightly opens (about 1 cm).  During labor, the cervix will change from closed and as firm as the tip of your nose to as stretchy and thin as your eyelid and open as large as your baby’s head.

A woman that has never birthed will have a cervical opening shaped like a circle, where a woman that has birthed vaginally before will have a cervical opening more like an oval.  The os is usually closed tight, especially with a mom that has never birthed before, and sealed off with cervical fluid (mucous).  The cervical fluid will change over the menstrual cycle to be thin and slippery at ovulation to allow for sperm to move through it easier for conception and to create lubrication for birth.  The fluid will get very thick during pregnancy (and is usually called a “plug”) to protect the uterus (and baby, if present) from anything harmful that might enter the vagina.  The mucous plug doesn’t just come out all at once during labor.  It is just thicker than usual, and your body continuously makes more, just as it does throughout your cycle.

The uterus wraps behind and above the bladder, while the cervix will change positions during your monthly cycle.  The cervix will point posterior (towards your back) and feel high with internal exam during peak fertility and during pregnancy.  It will move to point anterior (forward, centering in your vagina) and feel low during your period and at full dilation in labor.

The uterus is held in position by many ligaments (not just the round ligaments) that connect the cervix and uterine body to the sacrum, pelvis, and spine.  One very large ligament, the broad ligament, wraps the whole uterus and reproductive organs like a sheet and holds the uterus to the spine for stability.  If these ligaments get tight in various ways, it will twist the uterus and cervix and cause fertility imbalances, fetal positioning imbalances, as well as discomfort during your cycle, pregnancy, and birth.

Nourished blood flow to the uterus is imperative for a healthy cycle, uterine balance, and reproduction.  Nutrient-dense food brings balance to hormones. Hydration mobilizes the nutrients through the blood.  Whole-body balanced movement (especially in the core and pelvic region) allow these nutrients and oxygen to reach the uterus for optimal function.  What a complex organ women are created with!