What's happening
Your back is working harder than it ever has — with less support than it needs.
Lower back pain during pregnancy isn't just discomfort — it's your body giving you a clear signal that something in your structure needs support. Understanding what's causing it helps you address it rather than just manage it.
As your baby grows, your center of gravity shifts forward — often by 2 to 3 inches by the third trimester. To compensate, your lower back curves more sharply inward, a posture called anterior pelvic tilt. This posture shortens and tightens the muscles along your lumbar spine while lengthening and weakening the muscles in your abdomen and glutes that would normally balance them.
At the same time, a hormone called relaxin — which your body releases throughout pregnancy to prepare your pelvis for birth — loosens the ligaments and connective tissue throughout your body, including those that stabilize your spine and sacroiliac joints. A back that is working harder, with looser ligaments, under more load is the predictable result.
"Most pregnancy back pain originates at the sacroiliac joint — the joint where your spine meets your pelvis. When this joint loses stability, surrounding muscles compensate, which creates the characteristic deep, diffuse ache that worsens as the day goes on."
Why it gets worse
The things that intensify it — and why.
As the day goes on. Muscle fatigue accumulates throughout the day. By evening, the muscles supporting your spine have been working for hours and are less effective at their job.
With prolonged sitting or standing. Both positions lock your pelvis into a fixed posture, which increases pressure on the SI joint and lumbar discs over time.
In later trimesters. As baby grows and your uterus expands upward, the mechanical forces on your lower back increase. Most moms report pain beginning or worsening around 20 to 28 weeks.
In subsequent pregnancies. Your ligaments and supporting structures start from a more stretched baseline after each pregnancy, which is why back pain often appears earlier and feels more intense in second and third pregnancies.
What actually helps
Relief that addresses the source, not just the symptom.
Structural support — not just compression
Bands that wrap without providing structure give temporary comfort but don't address SI joint instability. Look for support that includes rigid or semi-rigid panels that target the sacroiliac joint directly.
Heat therapy for acute pain
Applying heat to the lower back for 15 to 20 minutes relaxes the muscles that have tightened in response to SI joint instability. A reusable gel pack is more practical than disposable heat patches throughout pregnancy.
Movement — not rest
Prolonged rest actually worsens pregnancy back pain in most cases. Gentle movement — walking, prenatal yoga, swimming — maintains circulation and prevents muscle stiffening. The key is moving with support.
Pelvic floor physical therapy
A pelvic floor PT can assess whether your back pain has a pelvic floor component — which is common — and give you specific exercises that address the root cause rather than just the symptoms.
Talk with Jenn about your back pain
Tell Jenn what you're experiencing and she'll explain what's happening in your body and which Body After Baby product fits your specific situation.
Talk with Jenn →Postpartum
After delivery — why back pain often continues or returns.
Many moms expect back pain to resolve after delivery. For some it does — but for many, it persists or even worsens in the early postpartum period. There are several reasons for this.
Relaxin continues to circulate in your body for three to six months after delivery in non-breastfeeding moms and potentially longer in those who are breastfeeding. Your ligaments are still looser than normal, which means the SI joint instability that caused back pain during pregnancy doesn't resolve overnight.
The postural patterns your body adopted during pregnancy — anterior pelvic tilt, rounded upper back, forward head position — become habitual. Without active correction they persist long after delivery.
Add to this the postural demands of early motherhood — feeding, carrying, bending over a bassinet — and it becomes clear why postpartum back pain is so common and so persistent.