During pregnancy, the uterus rises from deep inside the pelvis to high in the abdomen, reaching nearly to the base of the ribcage by the final weeks. This journey upward is one of the most dramatic physical changes in the human body, and the uterus’s position at any given point serves as a reliable marker of how far along the pregnancy has progressed.
First Trimester: Inside the Pelvis
Before pregnancy, the uterus sits low in the pelvis, roughly behind the bladder and in front of the rectum. It’s about the size of a small pear. In the earliest weeks, from around six to seven weeks, the uterus begins to grow and shifts from its usual pear shape to a more egg-like form. You wouldn’t be able to feel it from the outside yet because it’s still tucked behind the pubic bone.
By 12 weeks, the uterus has grown to roughly the size of a grapefruit and completely fills the pelvic cavity. At this point, the top of the uterus (called the fundus) just barely rises above the pubic bone, the bony ridge you can feel at the very lowest part of your abdomen. This is typically the first time a healthcare provider can begin to feel the uterus by pressing on your belly rather than relying solely on an internal exam.
Second Trimester: Rising to the Belly Button
Once the uterus clears the pelvis, it grows steadily upward through the abdomen. The key landmark here is the belly button. By 20 weeks, the fundus reaches the level of the navel. This is also the point when a simple rule of thumb kicks in: the distance from the pubic bone to the top of the uterus, measured in centimeters, roughly matches the number of weeks of pregnancy. At 24 weeks, that measurement is about 24 centimeters. A difference of more than 3 centimeters in either direction can signal that the baby is growing faster or slower than expected, which is why providers check this at every prenatal visit.
As the uterus rises through the second trimester, you may feel a sharp or aching sensation in your lower abdomen, hips, or groin. This is round ligament pain, caused by two rope-like bands of tissue on either side of the uterus stretching to support its increasing weight. The pain often flares during sudden movements like standing up quickly or rolling over in bed. It’s one of the most common physical reminders that the uterus is actively changing position.
Third Trimester: Up to the Ribcage
The uterus continues climbing through the third trimester. By around 36 weeks, the fundus reaches the xiphoid process, the small piece of cartilage at the very bottom of your breastbone. At this point the uterus takes up a significant portion of the abdominal cavity, and its sheer size pushes surrounding organs out of their usual positions.
The diaphragm, the dome-shaped muscle that controls breathing, gets pushed upward. This reduces lung capacity and is the main reason many women feel short of breath in late pregnancy. The heart shifts to the left and slightly higher in the chest. The stomach and intestines get compressed and displaced upward as well, contributing to heartburn and the feeling of fullness after small meals. The bladder, sitting directly below the uterus, gets squeezed from above, which is why the frequent need to urinate that eased up in the second trimester often returns with a vengeance.
Lightening: The Final Descent
In the last weeks before delivery, the baby’s head typically drops lower into the pelvis in preparation for birth. This shift is called lightening, and it moves the fundus back down from its highest point. For first-time mothers, lightening usually happens two to four weeks before delivery, though it can occur earlier. For women who have given birth before, the baby often doesn’t drop until labor actually begins.
Lightening can bring noticeable relief. Breathing gets easier as pressure on the diaphragm decreases, and heartburn may improve. The tradeoff is increased pressure on the bladder and pelvis, which can make walking feel different and send you to the bathroom even more frequently. Some women describe a distinct feeling of heaviness low in the pelvis. Others barely notice it happened until a provider points out that the baby has moved down.
What Happens if Your Uterus Is Tilted
About 20 to 30 percent of women have a retroverted, or “tilted,” uterus, meaning it angles backward toward the spine rather than forward toward the belly. This is a normal variation and doesn’t affect fertility or the ability to carry a pregnancy. As the uterus grows during the first trimester, it naturally shifts forward into the standard position to make room for the baby.
In rare cases, a retroverted uterus fails to make this shift and becomes trapped in the pelvis, a condition called uterine incarceration. When this happens, the uterus can’t expand properly and may cause pain, difficulty urinating, or other complications. It’s uncommon enough that most women with a tilted uterus never experience it, but it’s the reason providers monitor uterine position in early pregnancy.
After Delivery: The Return
Once the baby and placenta are delivered, the uterus begins shrinking back toward its original size and position. This process, called involution, happens fastest in the first 30 days. You can sometimes feel the uterus as a firm, grapefruit-sized mass near your belly button in the hours after birth, and over the following days it descends rapidly back into the pelvis.
For first-time mothers, the uterus typically returns close to its pre-pregnancy size within about six weeks. For women who have had multiple pregnancies, involution follows the same pattern but tends to take a bit longer, around six to eight weeks or more. The cramping some women feel while breastfeeding in those early postpartum days is the uterus actively contracting as part of this process.