At 13 weeks pregnant, your uterus is roughly the size of a large grapefruit, measuring about 10 to 12 centimeters (4 to 5 inches) from top to bottom. It has grown significantly from its pre-pregnancy size, which is closer to a small pear, and the top of the uterus (called the fundus) is now sitting right around the level of your pubic bone or just above it.
Where Your Uterus Sits at 13 Weeks
For most of the first trimester, the uterus stays tucked deep inside the pelvis, hidden behind the pubic bone. Around 12 to 13 weeks, it begins to rise above the pelvic rim and shift upward into the abdominal cavity. This is the transition point where a small baby bump may start to become visible as the uterus grows upward and outward.
At about 12 weeks, the top of the uterus sits in nearly the same spot as the pubic bone. By 13 weeks, it has typically crept just above that landmark. This upward shift is why many women notice a welcome change right around this time: the constant urge to pee eases up. The uterus is literally moving away from the bladder, relieving the pressure that made those frequent bathroom trips necessary during the first trimester.
How 13 Weeks Compares to Other Stages
To put the size in perspective, here is how the uterus changes over a full pregnancy:
- Pre-pregnancy: About the size of a small pear, roughly 7 to 8 centimeters long.
- 8 weeks: About the size of a large orange.
- 13 weeks: About the size of a large grapefruit, around 10 to 12 centimeters.
- 20 weeks: Reaches the belly button, roughly the size of a cantaloupe.
- 36 to 40 weeks: Extends up near the rib cage, roughly the size of a watermelon.
The growth from here accelerates. Between 13 and 20 weeks, the uterus will roughly double in height, rising from just above the pubic bone all the way to the navel. That rapid expansion is why many women transition out of regular pants during this stretch.
Why Your Bump May Not Match the Size
Even though the uterus is a consistent size at 13 weeks from one pregnancy to the next, the visible bump varies a lot between women. Several factors affect what you see on the outside. Your height, torso length, core muscle tone, and whether this is your first pregnancy all play a role. Women who are taller or have a longer torso often show later because the uterus has more vertical space to grow before it pushes outward. If you have been pregnant before, your abdominal muscles are more relaxed, so a bump tends to appear earlier.
Body weight and the position of the uterus (tilted forward versus tilted backward) also matter. Some women at 13 weeks have a noticeable bump, while others look almost the same as before. Both are normal.
What Your Baby Looks Like Inside
At 13 weeks, the baby is about 7 to 8 centimeters long from head to bottom (roughly the length of a peapod) and weighs around 23 to 25 grams. The head still makes up about a third of the total body length, but the rest of the body is catching up fast. Fingers and toes are fully separated, and the bones are beginning to harden. The kidneys are starting to produce urine, which gets released into the amniotic fluid.
There is also a lot more blood circulating through your pelvic area to support this growth. By the end of pregnancy, your blood volume will increase by nearly 50 percent, and that process is already well underway at 13 weeks.
When Uterine Size Gets Measured
You might expect your doctor or midwife to start measuring your uterus at this stage, but formal measurements typically don’t begin until about 20 weeks. Before that point, the top of the uterus isn’t high enough above the pubic bone for an external tape measurement to be reliable. At your 13-week visits, your provider may feel for the fundus with their hands to confirm it is roughly where it should be, but the centimeter-by-centimeter tracking with a measuring tape comes later.
Once those measurements start at 20 weeks, the math is straightforward: the distance in centimeters from the pubic bone to the top of the uterus roughly equals the number of weeks you are pregnant. At 28 weeks, for example, the fundal height is typically around 28 centimeters. If the measurement is off by more than 2 to 3 centimeters in either direction, your provider may order an ultrasound to check on baby’s growth or amniotic fluid levels.