Rib pain during pregnancy typically starts in the third trimester, from around 28 weeks onward. It’s one of the most common discomforts of late pregnancy, driven by a combination of your expanding uterus, hormonal changes, and the physical repositioning of your ribcage to make room for a growing baby.
Why the Third Trimester Is the Turning Point
The 28-week mark is when most pregnant people first notice rib soreness, and there’s a straightforward reason: that’s when the top of the uterus climbs high enough to start pressing against the lower ribs. By around 36 weeks, the top of the uterus reaches the breastbone, its highest point during pregnancy. That upward pressure pushes the diaphragm and lower ribs outward, creating a dull ache, sharp twinges, or a feeling of constant pressure along the bottom of the ribcage.
Some people notice mild discomfort earlier, in the late second trimester, especially if they’re carrying multiples or have a shorter torso. But for most single pregnancies, the pain becomes noticeable only once the baby is large enough for the uterus to crowd the rib area.
What’s Physically Happening to Your Ribs
Your ribcage doesn’t just feel different during pregnancy. It literally changes shape. Research suggests the ribs expand an average of 2 to 3 inches as the diaphragm gets displaced upward and outward. The angle where your lower ribs meet at the center of your chest (called the infrasternal angle) widens in every pregnancy. Normally, that angle sits around 90 degrees. During pregnancy, it can push past 110 degrees, a measurement sometimes called “rib flare.”
This expansion starts gradually in the second trimester but becomes most pronounced, and most uncomfortable, in the third. A hormone called relaxin plays a key role. Produced by the ovaries and placenta, relaxin loosens muscles, joints, and ligaments throughout pregnancy so your body can stretch and accommodate the baby. Relaxin levels peak around 12 to 14 weeks, meaning the softening of your rib cartilage and connective tissue begins well before you feel any pain. The discomfort comes later because it takes time for the uterus to grow large enough to push against that already-loosened ribcage.
How Baby’s Position Affects the Pain
Where you feel rib pain can depend on how your baby is positioned. In a head-down (vertex) position, the baby’s feet are up near your ribs, and kicks or stretches can cause sharp, sudden jabs under the ribcage. This is the classic “baby kicking my ribs” sensation that peaks in the weeks before the baby drops lower into the pelvis, usually around 36 to 38 weeks in a first pregnancy.
If your baby is breech (feet or bottom down), you’re more likely to feel a hard lump pressing against your ribs instead, which is the baby’s head. You might notice kicks lower, in your pelvis, rather than under your ribs. Interestingly, a breech position doesn’t typically make pregnancy more painful overall. The sensations are simply in different locations.
What Normal Rib Pain Feels Like
Normal pregnancy-related rib pain is usually a broad, achy pressure along the lower ribs, often worse on one side. It tends to flare up when you’re sitting for long periods, especially if you’re slouched, and may ease when you stand, stretch, or change position. Some people describe it as a bruised feeling, others as a tight band around the lower chest. It can also feel like a stitch in your side that doesn’t go away.
The pain commonly worsens as the day goes on, since gravity and fatigue both contribute to the pressure. Lying on the side opposite to the pain often brings some relief. Many people find that rib pain eases significantly in the final weeks of pregnancy when the baby “drops” into the pelvis (called lightening), which shifts the uterus downward and takes pressure off the ribs.
When Rib Pain Signals Something Else
Most rib pain in pregnancy is musculoskeletal and harmless. But pain specifically in the right upper abdomen, just below the ribs, deserves attention because it can indicate two conditions that require medical evaluation.
The first is preeclampsia, a serious blood pressure condition. Pain from preeclampsia typically feels like a deep ache or pressure in the upper right abdomen or just below the breastbone. It’s caused by liver involvement and often comes with other warning signs: sudden swelling in the face or hands, persistent headaches, vision changes, or nausea. This type of pain can appear any time after 20 weeks but is most common in the third trimester.
The second is gallbladder problems. Pregnancy increases the risk of gallstones, and gallbladder pain also localizes under the right ribs. The key distinction is timing: gallbladder pain typically worsens after eating fatty meals and may come in intense waves rather than a constant ache.
If your rib pain is only on the right side, comes on suddenly, or is accompanied by any of the symptoms listed above, it’s worth a call to your provider to rule out these conditions.
Ways to Ease the Discomfort
A simple side-bending stretch can take pressure off the ribs. While seated, bend your upper body sideways, away from the side that hurts. Raise the arm on the painful side above your head, hold the stretch for a few minutes while breathing deeply, then relax back to a neutral position. This creates space between the ribs and the top of the uterus and can offer immediate, if temporary, relief.
Deep breathing exercises throughout the day also help by gently mobilizing the ribcage and preventing the muscles between the ribs from tightening up. Practicing this before bedtime can make sleeping more comfortable, since rib pain often peaks when you’re lying down.
Beyond stretching, a few practical adjustments make a difference. Sitting upright rather than slouching keeps the uterus from pressing as directly into the ribs. Wearing loose clothing and a supportive (not restrictive) bra reduces external pressure. Some people find that getting on all fours for a few minutes allows the belly to hang forward, temporarily relieving rib compression. A prenatal physiotherapist can tailor exercises to your specific pain pattern and body mechanics if the discomfort is interfering with sleep or daily activities.
After Delivery: Does the Ribcage Go Back?
For most people, rib pain resolves quickly after birth once the uterus shrinks and the mechanical pressure disappears. The ribcage itself does narrow again, but not always completely. Some rib widening can persist, especially without targeted postpartum exercise. Guided core and breathing rehabilitation can help the ribs return closer to their pre-pregnancy angle, particularly if rib flare (an angle wider than 110 degrees) developed during pregnancy.