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Mild low back pain is common during pregnancy. It happens due to stretch on the uterosacral ligaments that support the uterus. The growing uterus causes the stretch and strain on the supporting ligaments. If it is not associated with spotting/bleeding, abdominal cramps or increasing intensity, then you can relax. If any of associated symptoms develop, visit your gynecologist/obstetrician for a thorough evaluation at the earliest. If the uterus is found to be active, then you might be started on uterine relaxants (it is safe to take during pregnancy) to help you continue with the pregnancy smoothly. Take adequate rest. Drink plenty of water. Maintain healthy diet. Avoid any heavy work. Avoid having intercourse during first trimester. Avoid lifting heavy objects and climbing stairs or standing for long periods.
Take care.