Pregnancy | Why Does My Back Hurt?

Back pain is an exceedingly common complaint during pregnancy, with over 50% of pregnant women experiencing some degree of back discomfort. Understanding the various causes of back pain can help women cope with this troublesome symptom.

Main Causes of Back Pain in Pregnancy

Several key factors contribute to back pain during the 40 weeks of pregnancy, resulting from the major physical changes a woman’s body undergoes to support fetal growth and development.

Hormonal Changes

Hormones like relaxin and progesterone play a major role in causing the ligaments, muscles and joints to relax and loosen during pregnancy. This leads to increased mobility in the pelvic region and lower back, but also instability and pain.

The hormone relaxin increases tissue elasticity in preparation for childbirth. But it also softens the ligaments supporting the spine and pelvis, straining these structures.

Likewise, elevated progesterone relaxes muscles and loosens ligaments, placing extra strain on the back. These effects become more pronounced as pregnancy advances, with pain typically worsening in the later trimesters.

Physical Changes

A woman’s posture and weight distribution gradually shift to accommodate the growing baby, increasing stress on the lower back. Common physical changes include:

Postural Changes

As the uterus expands, a pregnant woman’s center of gravity rotates forward. To counterbalance this, expectant moms tend to arch their lower back and lean slightly backward. This overextends the spine and strains the supporting muscles.

The pelvis also tilts forward from the added weight in front, exacerbating back curvature. These postural adjustments incrementally increase stress on the lower back and sacroiliac joints.

Weight Gain

The extra pounds gained during pregnancy places substantial weight on the spine and hips. Most women gain 25-35 pounds over the 40 week gestation period, which directly increases the lower back’s workload.

This extra stress on the back combined with loosened ligaments and muscles leads to pain, especially evident late in pregnancy when women carry the most weight.

Muscle Separation

As the uterus grows upwards and forwards, it can push apart the large parallel bands of abdominal muscles running down a woman’s midline. This split is termed diastasis recti.

With the abs stretched thin and weakened, they provide less essential support for correct spinal alignment. The back must bear more strain as a result, leading to pain.

Expanding Uterus

The expanding uterus significantly contributes to back discomfort in several ways:

Firstly, its upward growth shifts abdominal organs and presses outwards against other internal structures. This places indirect pressure on the muscles, nerves and blood vessels of the lower back.

Secondly, the sheer weight of the gravid (pregnant) uterus strains the pelvis and lumbar spine. Towards the end of pregnancy, the uterus can weigh over 20 pounds!

And thirdly, as the uterus enlarges, it can compress or restrict key nerves and blood vessels supplying the pelvis and legs. This leads to numbness, tingling and shooting leg pains.

Stress on Lower Body

Supporting a pregnancy induces anatomical changes in the lower spinal curvature as well as the shape and width of the pelvis. These changes alter weight distribution and stability, increasing stress on the back.

Increased Lumbar Curve

Pregnancy hormones and postural adaptations over-curve the lower (lumbar) spine, disturbing normal muscle and ligament balance.

As this lumbar lordosis progresses, the small facet joints linking the vertebrae become angled sideways, leading to pinching and inflammation of adjoining structures.

Pelvic Changes

The hormone relaxin widens the pelvic circumference up to 35% to accommodate delivery of the infant. This widening separates the sacroiliac joints and strains the ligaments holding the pelvis together.

Uneven pelvic expansion combined with looser ligaments causes the pelvis to become rotationally and vertically unstable. This pelvic instability translates into lumbar and sacral back pain.

Other Contributing Factors

Several other issues can exacerbate back discomfort during pregnancy, including underlying medical conditions, increased activity levels and anatomical variations.

Medical Conditions and Complications

Certain common medical complications arise more frequently during pregnancy and contribute to back pain for expectant mothers. These include:

Sciatica

Lower back pain radiating downwards into the buttocks and thighs affects over 30% of pregnant women. This pain results from inflammation or compression of the large sciatic nerve running through the back of each thigh.

In later pregnancy, the expanding uterus can directly squeeze this nerve or cause back strain that pinches associated nerve roots, producing the signature leg pains of sciatica.

Herniated Discs

Occasionally the heightened spinal strain from pregnancy may rupture one of the discs cushioning the vertebrae. This causes the gel-like disc material to extrude outwards in a herniated disc.

A herniated disc inflames nearby spinal nerves, generating sharp back pain coupled with numbness and weakness.

Osteoporosis

Very uncommonly, the bones supporting the lower back weaken substantially during pregnancy from depleted calcium levels. This condition, called pregnancy-associated osteoporosis, precipitates fractures and intense pain.

Daily Activities

Performing routine activities with poorer spinal alignment, looser ligaments and extra pregnancy weight often aggravates back discomfort.

Bending, lifting heavy objects and ambulating up stairs or inclined surfaces tends to intensify pain. Sleeping incorrectly can also worsen symptoms overnight.

Other Factors

• Ectopic pregnancy: Life-threatening rupture of a fallopian tube fetus can cause sudden, intense low back and abdominal pain.
• Infections: Flank and low back pain may signal a kidney infection like pyelonephritis, especially coupled with fever.
• Placental position: A rare posterior placenta lying near the back of the uterus may directly cause localized low back pain.

Managing and Preventing Pain

While not completely avoidable, certain lifestyle measures and treatments can alleviate pregnancy’s strain on the lower back.

Improving posture, strengthening core muscles, utilizing supports and maintaining fitness all help take pressure off the spine and relieve discomfort. Heat, massage, chiropractic care and acupuncture also provide symptom relief.

If back pain fails to improve or worsens despite such measures, promptly consult your physician – severe or sustained pain may reflect an underlying complication requiring prompt evaluation. But fortunately, for most women, pregnancy-related back pain gradually resolves over the first several months postpartum.

When to Seek Medical Care

Contact your healthcare provider right away about sudden or progressively worsening back pain, especially if accompanied by:

• Leg numbness or weakness
• Fever or chills
• Vaginal bleeding
• Nausea/vomiting
• Difficulty urinating

These red flags may indicate a serious medical issue requiring urgent medical attention to safeguard maternal and fetal health.

Conclusion

Back pain frequently accompanies pregnancy but generally resolves by 6 months postpartum. Hormonal effects relaxing the lower back and pelvis combine with postural shifts, extra weight and abdominal changes to strain the spine and sacroiliac joints.

Understanding the factors provoking pain allows women to take preventative measures to reinforce proper spinal alignment and muscle strength. While expected back soreness proves inevitable for some pregnant women, simple supportive therapies and lifestyle adjustments can mitigate symptoms.