Most pregnancy back pain is mechanical and unremarkable: ligaments loosen, the bump pulls you forward, and your lower back spends nine months compensating. It is miserable and it is not a sign of anything.
The reason it still needs a triage page is that three other things present as back pain, one of them is preterm labour, and the feature that separates them is not severity. It is rhythm.
The short answer: a dull lower-back ache that is worse by evening, worse after standing, and eased by rest and position changes is normal in pregnancy and affects around half of them. What is not normal: pain that comes in regular waves before 37 weeks (possible preterm labour), pain with fever or burning when you pee (possible kidney infection), or back pain with any vaginal bleeding. Those are same-day calls. Paracetamol is the usual painkiller; ibuprofen is avoided after 20 weeks.
Why it happens
Relaxin does what its name says — it softens the ligaments holding the pelvis together, in preparation for birth. Useful later, destabilising now. At the same time the uterus grows forward and the natural curve of the lower back deepens to compensate, which loads the muscles and the small joints of the lumbar spine. Add the weight gain and the fact that most people stop doing whatever exercise used to hold their core together, and the ache is close to inevitable.
That is why it starts in the second trimester rather than the first, and why it usually peaks in the third: the mechanical load is what drives it, and the mechanical load only goes one way.
What is normal
| Ordinary back pain | Ring about it | |
|---|---|---|
| Pattern | Continuous ache, varies with activity | Comes in waves at measurable intervals |
| Timing | Worse at the end of the day | Wakes you, or builds regularly through the night |
| Position | Eases lying on your side | No position helps at all |
| With it | Nothing else | Fever, burning urination, bleeding, fluid loss, or reduced movements |
| Where | Broad, across the lower back | One side only, high up around the kidney |
The one thing worth doing before you ring
If the pain is coming and going rather than sitting there, time it for an hour. Write down when each wave starts, how long it lasts, and the gap to the next. Ordinary back pain will not produce a pattern. Preterm labour will, and the person who answers the phone will ask you for exactly those numbers — arriving with them changes a vague call into a specific one.
Call your maternity unit the same day if: the pain comes in regular waves and you are under 37 weeks; you have a fever, chills, or burning when you pee alongside it; there is any vaginal bleeding; you have a gush or trickle of fluid; you notice reduced movements; or the pain is severe, sudden and unlike anything before it. Do not wait for the morning for any of these.
Call emergency services if the back pain comes with weakness in both legs, numbness around the saddle area, or any change in bladder or bowel control — that is a spinal emergency and is covered on the sciatica page.
Back pain in pregnancy — at a glance
Around half of pregnancies involve back pain, driven by relaxin loosening the pelvic and spinal ligaments and by the growing uterus shifting the centre of gravity forward. Ordinary pregnancy back pain is a continuous dull ache across the lower back, worse by evening and after standing, eased by rest and by side-lying with a pillow between the knees. Three patterns are not that: rhythmic waves at measurable intervals before 37 weeks, which is how preterm labour often presents; one-sided pain high around the kidney with fever or burning urination, which is a kidney infection; and back pain with any vaginal bleeding. Each of those is a same-day call, and timing the waves for an hour beforehand gives the maternity unit the numbers it will ask for. Paracetamol at the lowest effective dose is the usual painkiller and ibuprofen is avoided after 20 weeks. Weakness in both legs, saddle numbness, or any change in bladder or bowel control is an emergency rather than a call.
Inside Baby Novum: the contraction timer records start times, durations and intervals — it does not care whether you are timing a tightening or a wave of back pain. Sessions stay encrypted on the device with a hardware-backed key, with no account and no server holding a copy.
Frequently Asked Questions
Is back pain normal in pregnancy?
Yes — it affects roughly half to two-thirds of pregnancies. Relaxin loosens the ligaments that stabilise the pelvis and spine, the bump shifts your centre of gravity forward, and the muscles of the lower back take up the difference. The result is a dull ache that is worse at the end of the day, worse after standing, and better for rest and a change of position.
When is back pain in pregnancy a warning sign?
Three patterns. Rhythmic — coming in waves that arrive at regular intervals, especially before 37 weeks, which can be preterm labour and back pain is a common way it presents. Feverish — one-sided pain around the kidney area with a temperature or burning when you pee, which is a kidney infection. Bleeding — back pain with any vaginal bleeding. All three are calls, not appointments.
How do I tell back pain from contractions?
Time it. Ordinary back pain is there — it varies with what you are doing but does not have a shape. Contractions have a beginning, a peak and an end, they last a fairly consistent number of seconds, and the gaps between them are measurable. If you can write down "60 seconds, then 6 minutes, then 60 seconds" you are timing something, and before 37 weeks that is a call.
Is it back pain or pelvic girdle pain?
Location and trigger. Back pain is a broad ache across the lower back. Pelvic girdle pain is sharper and sits in the pubic bone, the hips or the joints either side of the base of the spine, and it is provoked by specific movements — getting out of a car, rolling over in bed, climbing stairs one leg at a time. PGP is treated by physiotherapy and is worth naming, because it gets written off as ordinary back pain constantly.
What can I take for back pain in pregnancy?
Paracetamol at the lowest effective dose for the shortest time is the usual option. Ibuprofen and other NSAIDs are avoided after 20 weeks and generally avoided earlier too. Most of what helps is not a tablet: a warm bath, side-sleeping with a pillow between the knees, avoiding standing still for long periods, and physiotherapy — which in many places you can be referred to, or self-refer.