Why Your Low Back and Pelvis Still Hurt Months After Delivery: Sacroiliac Joint Pain, Hormone Loosening, and the Right Way to Stabilize

Many people assume that pelvic pain after pregnancy is just part of recovery and that it will fade on its own. Sometimes it does. But sometimes it does not. For a lot of new mothers, the pain that sits low and off to one side of the spine, or right over the back of the buttock, is not coming from the spine at all. It is coming from the sacroiliac joint.

The sacroiliac joint is the joint where the sacrum (the triangular bone at the base of the spine) meets the ilium (the big pelvic bones on each side). You actually have two sacroiliac joints, left and right. These joints are built less like a freely moving hinge and more like a heavily reinforced seam. They are held together by very tough ligaments and layers of muscle, and their job is to transfer load between the spine and the legs every time you walk, climb stairs, squat, or pick up a baby.

During pregnancy, that reinforced seam is intentionally loosened by hormones. After delivery, you are suddenly expected to lift, carry, twist, breastfeed, bend into car seats, and stand holding a baby on one hip. You are doing all of this at a time when the sacroiliac joint is still more mobile than usual and the stabilizing muscles of the deep core are not yet back online. This combination is exactly why sacroiliac joint pain after pregnancy is so common, so intense, and so stubborn.

A healthy sacroiliac joint is supposed to allow only a tiny amount of motion — think millimeters, not centimeters. The ligaments that cross the joint are designed to be almost seatbelt-strong. In pregnancy, however, the body intentionally softens and lengthens many ligaments in the pelvis to prepare for delivery. This is largely influenced by hormones such as relaxin and progesterone, which increase connective tissue laxity so that the pelvis can widen and the baby can pass through.

This increased laxity is not only at the pubic symphysis in the front of the pelvis. It also affects the sacroiliac joints in the back. When those joints loosen, they become less like a locked seam and more like a slightly wobbly hinge.

Here is why that matters:

• A looser sacroiliac joint can shear — meaning one surface can glide slightly in relation to the other. That tiny shift can irritate the dense nerve endings in the ligaments around the joint, creating sharp, localized pain.
• A looser sacroiliac joint stops absorbing load efficiently. Instead of distributing weight cleanly from the spine into the legs, the joint transmits force in a slightly unstable way. The body senses this mechanical “slip” as threat. Your brain interprets it as deep buttock pain or back-of-the-hip pain.
• A looser sacroiliac joint forces nearby muscles to go into constant tension to act like substitute ligaments. This can cause aching or burning in the gluteal muscles, piriformis area, and even down the back of the leg, which sometimes gets misdiagnosed as sciatica from a spinal disc even when the spine itself is normal.

The important detail is this: those hormones do not instantly “switch off” at delivery. The elevated laxity in the pelvic ligaments lingers into the postpartum period, often for months while breastfeeding, and sometimes longer if baseline joint hypermobility was present even before pregnancy.

So if you are six weeks, three months, even six months postpartum and still dealing with deep one-sided pelvic pain when you stand up holding the baby, this is not your imagination. Your stabilizers are behind schedule, and your ligaments are still on maternity leave.

Postpartum sacroiliac joint pain has a very specific fingerprint. Even though it can look like general “low back pain” from the outside, the way it behaves is different. These common patterns are often reported in clinical practice and pelvic rehab literature:

• 1. One-sided buttock or back-of-hip pain
  The pain usually sits just below the dimple you can feel at the back of the pelvis. You can often point to it with one or two fingertips. It is very common for it to be worse on the side you tend to carry the baby.
• 2. Pain when standing on one leg 
  Standing to put on pants, stepping into a car, going up stairs, or shifting weight to one leg while holding a baby can send a stab or deep ache through that joint. This is because the sacroiliac joint has to transmit your entire body weight plus the baby’s weight through one side at that moment.
• 3. Pain with rolling in bed or getting out of bed
  Your pelvis has to rotate and then lift as a unit, and if one sacroiliac joint is unstable, that motion can feel like a jab or catch. Many new mothers notice that nights are the worst because every diaper change and feeding means one more awkward bed exit.
• 4. Pain after sitting and then standing 
  Car seats, nursing chairs, couches, and low soft surfaces all position the pelvis in a slightly tucked, asymmetric posture. When you stand up after being “crooked” for a long time, the sacroiliac joint suddenly takes full load again, and that first step can feel like lightning.
• 5. A sense that the pelvis is “loose,” “uneven,” or “not aligned”
  Many postpartum patients can feel that one half of the pelvis is not tracking with the other, especially during walking or stairs. Even if that language sounds vague, it is often accurate: they are sensing shear at the sacroiliac joint.
• 6. Radiation that mimics sciatica 
  Irritation around the sacroiliac joint can irritate nearby nerves and muscles in the buttock. That tightness can refer pain partway down the leg. This sometimes gets blamed on a herniated disc, but the spinal exam is normal. The real generator is pelvic instability at the sacroiliac joint.

There are three main reasons sacroiliac joint pain persists in the postpartum period: hormones, load, and timing.

1. Hormones and ligament laxity linger

Even after birth, ligament laxity in the pelvis does not immediately snap back to pre-pregnancy stiffness. In fact, while breastfeeding, hormone patterns can continue to support a more relaxed connective tissue state. That means the sacroiliac joint may still be slightly more mobile than it used to be, even months later.

2. Load skyrockets

Before delivery, you were carrying load internally. After delivery, you are now carrying load externally — and asymmetrically. You are constantly hiking a baby (and then a heavier baby, and then a car seat, and then a carrier plus a diaper bag) on one hip. You lift strollers into car trunks. You lean and twist over cribs. Every one of those postures pushes one sacroiliac joint harder than the other.

3. Timing of muscle recovery lags behind demand

During pregnancy, the deep abdominal wall and pelvic floor stretch dramatically. The deep stabilizers, especially the lower portion of the transversus abdominis and the multifidus muscles along the spine, are the body’s built-in corset for the pelvis. They coordinate with the pelvic floor. After birth, they are underactive and sometimes inhibited, especially if there was a tear, episiotomy, cesarean section, or prolonged pushing phase. That means, when you suddenly go back to lifting, twisting, and carrying, you are doing it with passive ligaments that are still loose and active muscles that are still asleep. Instability plus load is a perfect recipe for ongoing sacroiliac joint pain.

Sacroiliac joint pain often gets mislabeled as “lumbar strain,” “lumbar disc issue,” or “postpartum low back pain.” The location can overlap, but the mechanics are different.

Low back pain that truly comes from the spine usually sits more centrally, may produce tingling or numbness below the knee if a nerve root is pinched, and often worsens with spinal flexion or extension in a more predictable pattern.

Sacroiliac joint pain is more likely to sit over the buttock where the spine meets the pelvis, stay mostly on one side, and spike during single-leg load or transitional movements like rolling, standing out of a car, or carrying a baby on one hip. In other words, sacroiliac joint pain behaves like an irritated load-transfer joint, not an irritated lumbar disc.

This matters because the plan for sacroiliac joint pain after pregnancy is not just “rest your back.” It is “stabilize the pelvis, then retrain the stabilizers.”

A lot of postpartum patients are told, “You just need to strengthen your core.” That sounds empowering, but for many women in the first months after delivery, it is backwards.

Imagine an unstable door hinge. Would you immediately start slamming the door to “strengthen it”? Or would you first hold it in alignment, reinforce it, and then practice smooth motion?

That is the logic behind the brace-to-strength plan.

A sacroiliac belt or pelvic support belt is a wide, firm strap worn low around the pelvis, not around the waist. When fitted correctly, it hugs the iliac bones and compresses the sacroiliac joints just enough to limit shear. Think of it as temporary scaffolding for a wobbly joint.

Benefits of a well-fitted sacroiliac belt in the early postpartum phase include:

• Immediate reduction in sharp sacroiliac joint pain during standing, walking, stairs, and baby carrying
• Easier ability to perform daily tasks without constant guarding
• Less protective muscle spasm in the buttock and low back because the joint is not slipping with every weight shift
• Psychological relief: “I can actually get through the day without feeling like my pelvis is about to give out”

This is not “becoming dependent on a brace.” This is using external stability while the internal stabilizers wake back up.

Once the sacroiliac joint is supported and pain is down to a tolerable level, you start retraining clean movement. The early goals are:

• Learning how to roll in bed, get out of bed, and get out of a car while keeping the pelvis moving as one unit instead of twisting through the sacroiliac joint
• Practicing sit-to-stand without dumping all weight into one hip
• Picking up the baby from the crib or floor using a hip hinge and both hands instead of torqueing the pelvis while twisted to one side

Pelvic floor physical therapists and postpartum rehab specialists often teach these strategies in the first few visits because they reduce daily micro-irritation and prevent constant flare-ups.

After the initial “do not flare it” phase, the next phase is gentle reactivation of the muscles that are supposed to stabilize the pelvis from the inside. That usually includes:

• The lower fibers of the transversus abdominis (the deep wrapping abdominal muscle that acts like an internal corset)
• The multifidus muscles (segmental stabilizers along the spine)
• The pelvic floor (which forms a sling at the base of the pelvis and coordinates with breath)

These muscles are not trained with high-intensity crunches. In fact, intense sit-ups and aggressive twisting early on can make sacroiliac joint pain worse because they yank on an already unstable segment. Instead, therapy often starts with low-load, precise activation drills such as controlled breath-linked lower abdominal bracing, gentle bridging with equal weight on both legs, and short-range hip abduction against light resistance while keeping the pelvis level.

The point is to remind the nervous system: “These are your built-in pelvic seatbelts. Use them.”

As pain decreases and base stability returns, you gradually layer in more load:

• Step-ups with perfect pelvic control (no hip drop)
• Controlled single-leg balance drills
• Squats and hinges while keeping both sides of the pelvis level
• Carry drills using both arms so you stop favoring one hip every time you hold the baby

This stage matters not only for healing now but also for prevention later. The more symmetrical and strong you become in your glutes, deep abdominals, and pelvic floor, the less your sacroiliac joints will get hammered during future lifting — including lifting a growing toddler, not just a newborn.

Most sacroiliac joint pain after pregnancy is mechanical and responds well to structured rehab. But you should seek medical care promptly if you notice any of the following:

• Numbness, weakness, or true loss of strength in one leg
• Loss of bowel or bladder control, or sudden inability to feel the pelvic floor
• Fever, chills, or a sense of being acutely ill along with new severe low back or pelvic pain (infection must be ruled out)
• Pain that shoots below the knee with tingling or burning in a narrow line down the leg, which could indicate direct nerve root compression in the spine rather than isolated sacroiliac joint irritation
• Pain so severe you cannot bear weight on one leg, even with a support belt

These are not typical of standard sacroiliac joint instability and should be evaluated urgently.

Yes. Once the sacroiliac ligaments have been stretched and once the brain has learned certain compensation patterns (for example, always hiking the right hip to carry a load), you are more likely to flare the same side in a later pregnancy. But that does not mean you are doomed.

Women who learn early pelvic support strategies in pregnancy — such as wearing a sacroiliac stabilizing belt during long standing, practicing symmetrical lifting, avoiding deep asymmetrical lunges late in pregnancy, and doing gentle deep core and pelvic floor activation under professional guidance — often report less severe sacroiliac joint pain with subsequent pregnancies. In other words, you can pre-hab the problem before it becomes disabling again.

There is a quiet psychological piece here that does not get enough attention. A lot of postpartum sacroiliac joint pain patients say some version of this: “It feels like my pelvis is not attached right. I feel unstable. I do not trust my body.”

That feeling is real. When the sacroiliac joints are lax, every step can feel slightly off. When every step feels slightly off, the nervous system stays in low-level alarm. That constant alarm is exhausting. It makes sleep worse, which slows tissue recovery, which makes pain feel louder. It is a loop.

This is why mechanical support early (the sacroiliac belt) plus guided activation of deep stabilizers matters not only physically but emotionally. The moment you regain control — “I can roll out of bed without wincing,” “I can carry the car seat without stabbing pain,” “I can nurse without my whole pelvis locking up afterward” — your nervous system starts to downshift out of panic mode. Less panic means less guarding. Less guarding means less pain.

1. Sacroiliac joint pain after pregnancy is common and mechanical. It is not “all in your head,” and it is not always “just back pain.” It is often a problem of ligament laxity and joint shear at the sacroiliac joint after months of hormone-driven loosening.
2. The reason it lingers postpartum is that hormones that relax ligaments do not vanish instantly, core and pelvic floor stabilizers are not yet rebuilt, and you are suddenly doing heavy, uneven lifting on a still-unstable pelvis.
3. The pain usually sits low and one-sided near the buttock, spikes during single-leg load (stairs, pants, car), and often flares with rolling in bed or standing up after nursing. That pattern is classic for sacroiliac joint irritation.
4. The smartest plan is not “just do core work.” The smartest plan is brace-to-strength:
   • Support the sacroiliac joint short-term with an external belt to reduce shear
   • Relearn daily motions that stop yanking on one unstable joint
   • Reactivate deep pelvic and core stabilizers in a controlled, low-load way
   • Then build strength and symmetry to handle the real-life loads of parenting without flaring the joint again
5. You should get urgent medical evaluation if you develop neurologic red flags like numbness or weakness, bowel or bladder changes, fever with severe back or pelvic pain, or inability to bear weight. Those are not typical of straightforward sacroiliac joint laxity and must be seen right away.

Postpartum sacroiliac joint pain is not a sign that your body is broken. It is a sign that your pelvis did its job for pregnancy and birth, and now it needs structured support, not guilt. With smart stabilization, gradual activation of the right muscles (not just random crunches), and load management during the heaviest parenting tasks, most people can get back to walking, lifting, and living without that stabbing buttock pain every time they stand up.

Also Read:

• What’s Behind Your Lower-Left Back Pain—Kidney Stone, Sacroiliac Joint Pain, or Muscle Strain?
• How Long Does SI Joint Pain Take To Heal & What Are The Best Medications For It?