Lower back pain is one of the most common experiences during pregnancy, and there are some straightforward reasons why. Understanding what is driving it can make it feel a lot less alarming and help you manage it more effectively.

A combination of changes working together

Pregnancy brings a set of physical changes that, in combination, place significant demand on the lower back. On their own, each change would be manageable. Together, they create a cumulative load that builds across the months.

The hormone relaxin, produced from early pregnancy, gradually loosens the ligaments around the pelvis and lower back. This prepares the body for birth but reduces the passive stability these structures usually provide. Your muscles then take on more of the job of supporting your spine and pelvis, and they feel it.

At the same time, your growing bump shifts your centre of gravity forward. Your lower back responds by increasing its natural curve, and the muscles running along either side of the spine work harder to keep you upright. By the third trimester, this postural shift is at its most pronounced and the load through the lower back is at its greatest.

Why some people feel it more than others

The degree of lower back discomfort varies considerably from person to person and across different pregnancies. How much load your lower back carries day to day, how you move, how long you spend sitting or standing, and how your body distributes the changes of pregnancy all play a part.

It is also common for lower back pain to shift in character across the trimesters. What feels like general stiffness in the earlier months may become a more specific ache in the lower back or across the pelvis as pregnancy progresses. Both are common responses to the changes your body is going through.

The pelvis plays a central role

The sacroiliac joints, where your pelvis meets your spine, are particularly affected by the combination of ligament loosening and increased load. Many people experience discomfort specifically in this area, sometimes described as a deep ache across the back of the pelvis or into the buttocks. This is distinct from the more central lower back ache that comes from postural load, though the two can overlap.

Understanding which part of your lower back is uncomfortable, and what tends to aggravate or ease it, is useful information for managing it well.

A few things to carry with you

• Lower back pain during pregnancy is common and has clear physical causes.
• Hormonal loosening, postural shift, and increased load on the spine combine across the trimesters.
• Discomfort often changes in character as pregnancy progresses, and that is to be expected.
• Knowing what aggravates and eases your pain is a useful starting point for managing it.

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