Pregnancy causes a wide range of symptoms across the body, including lower back pain. Lower back pain is often a natural response to weight gain and muscle changes during the third trimester but can occasionally be a sign of something else.

Lower back pain may develop at any time during pregnancy for several reasons, including hormonal changes, stress, and changes to body weight, muscles, and posture. Back pain is a common outcome of pregnancy and rarely a cause for concern. However, it can become uncomfortable and may suggest other health problems if it occurs with other symptoms.

Nausea, fatigue, swollen feet, sleep issues, urinary leaking, and mood changes can all occur along with back pain. Even though it is a natural outcome of a growing uterus, methods are available to soothe and prevent episodes of back pain.

This article explains some causes of lower back pain in the third trimester. It also explains how to manage the pain and when to contact a healthcare professional.

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Third-trimester lower back pain most often occurs due to weight gain, posture changes due to changes in a person’s center of gravity, and a condition called diastasis recti that leads to the separation of abdominal muscles.

According to a 2023 study, back pain is most common during the third trimester of pregnancy and develops in around 60–70% of all pregnancies. The study suggests this pain may become severe in around one-third of pregnant people.

Lower back pain may occur for other reasons earlier in pregnancy, including:

  • hormone changes
  • ligaments becoming softer and more flexible ahead of labor
  • stress

A 2023 review of 28 studies, including data from over 12,900 people, suggests that certain factors increase the chance of back pain during pregnancy, including:

  • a history of back pain
  • the age of an individual at the time of pregnancy, with a higher age linked to more of a risk of frequent back pain
  • the number of pregnancies a person has had before

Weight gain

Weight gain is a natural part of pregnancy. However, it can play a role in lower back pain and painful joints.

According to the 2023 review above, a person’s weight may increase by 24.25–26.45 pounds (lb) or 11–12 kilograms (kg) on average. The 2023 study above found that individuals with lower back pain during pregnancy had a higher BMI on average than those who did not experience back pain.

The Centers for Disease Control and Prevention (CDC) recommends gaining weight in the following amounts, depending on body weight before pregnancy.

BMI before pregnancyRecommended weight gain for pregnancy with one infantRecommended weight gain for pregnancy with twins
Underweight: Lower than 18.528–40 lb (12.7–18.14 kg)50–62 lb (22.68–28.12 kg)
Normal weight: 18.5–24.925–35 lb (11.34–15.86 kg)37–54 lb (16.78–24.5 kg)
Overweight: 25.0–29.9 15–25 lb (6.8–11.34 kg)31–50 lb (14.06–22.68 kg)
Obesity: 30 and over11–20 lb (4.99–9.07 kg)25–42 lb (11.34–19.05 kg)

The flaws of BMI

BMI is a calculation of a person’s body fat based on their height and weight. However, studies suggest it is a poor indicator of a person’s body fat percentage.

It can be misleading because the measure does not account for overall body composition. The BMI measurement overlooks bone density, muscle mass, and other considerations.

For additional information, talk with your doctor about other body fat assessment methods.

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Learn more about weight gain in the third trimester.

A shifted center of gravity and posture changes

Individuals may lean back and adjust their posture as the growing fetus moves the center of gravity toward the front of the belly, according to a 2019 review. In the third trimester, a pregnant person also risks increased lumbar lordosis (a steeper inward curve in the lower back). Both of these may contribute to lower back pain.

Diastasis recti

Diastasis recti causes changes to the abdominal muscles, known as the rectus abdominis muscles. It is most common in the second or third trimester as the fetus grows.

Specifically, the fetus may push against the two parallel stretches of muscles in the abdomen. They are usually connected, but this extra pressure may cause them to separate. Part of their role is keeping the spine stable. This means that diastasis recti can increase a person’s risk of lower back pain or injury.

According to the American College of Obstetrics and Gynecology (ACOG), it may be wise to speak with a healthcare professional about back pain during pregnancy if the pain becomes severe or lasts for longer than 14 days. They will be looking to rule out underlying causes of lower back pain.

Back pain can also be a sign of early labor if it happens in the second or third trimester. If it occurs alongside other symptoms of high blood pressure during pregnancy, or preeclampsia, lower back pain might also suggest problems with the liver.

Learn about the signs of labor.

Lower back pain in late pregnancy can be uncomfortable and affect quality of life, but several approaches can help to reduce pain. These include:

  • resting
  • doing gentle exercise, such as yoga
  • using maternity support pillows while sitting
  • having massages or warm baths
  • having a firm, supportive mattress
  • attending individual or group maternity spine care classes
  • taking acetaminophen, although it is best to check with a healthcare professional that pain relief medications are safe for a particular pregnancy
  • not lifting objects that are too heavy
  • being careful to bend the knees and keep the back straight when lifting objects
  • moving the feet during turning, which can help to prevent twisting of the spine
  • wearing flat-soled footwear, which can support even weight distribution

Learn more about third-trimester pains and managing them.

Back pain is a common issue in the third trimester.

However, if it occurs along with the following symptoms, a person should contact a healthcare professional:

  • leaking fluid or blood from the vagina
  • sudden, severe swelling in the fingers, hands, or face
  • long lasting, painful headaches
  • stomach cramps or pain
  • fever
  • chills
  • persistent vomiting
  • painful, burning urination
  • blurred vision or vision problems
  • dizziness
  • feeling the baby move less than usual
  • thoughts of self-harm or hurting the baby

The following are answers to some questions people frequently ask about back pain in pregnancy.

Does lower back pain mean labor is near?

Lower back pain can be a sign of early labor, although it more commonly occurs due to weight gain, posture changes, and diastasis recti.

Where is preeclampsia back pain?

Preeclampsia pain commonly causes pain in the shoulder and upper abdomen. However, lower back pain might occur along with these symptoms if it has caused problems with the liver.

Lower back pain is common at all stages of pregnancy but occurs most often in the third trimester. It usually means that increased body weight or adjusted posture is putting pressure on the lower spine.

Lower back pain can also point to a condition called diastasis recti that causes separation of the abdominal muscles, reducing back support.

Measures such as gentle exercise, adjustments to load-bearing and movement, and supportive pillows and mattresses may help to relieve back pain.

Speak with a healthcare professional about severe or persistent lower back pain or discomfort that occurs alongside other symptoms, such as vomiting, upper shoulder and abdominal pain, headaches, and dizziness.