What causes frequent uterine contractions in the third trimester of pregnancy?

Increased uterine contractions during the third trimester are common and often reflect normal physiological changes as the body prepares for labor. These contractions—commonly referred to as Braxton Hicks contractions—are typically irregular, painless or mildly uncomfortable, non-rhythmic, and do not cause cervical dilation or effacement. They may be triggered by dehydration, physical activity, a full bladder, or sexual intercourse, and usually subside with rest, hydration, or position change.

However, frequent or intensifying contractions warrant careful evaluation, particularly if they occur more than four times per hour, become progressively stronger or more painful, follow a regular pattern (e.g., every 5–10 minutes), last longer than 60 seconds, or are accompanied by other warning signs such as vaginal bleeding or fluid leakage, pelvic pressure, lower back pain, or decreased fetal movement. These features may indicate preterm labor (before 37 weeks) or the onset of term labor—and require prompt obstetric assessment.

Other potential contributors to heightened uterine activity include urinary tract infections, placental abnormalities (e.g., placental abruption or previa), maternal stress or fever, or underlying medical conditions such as gestational hypertension or preeclampsia. A thorough clinical evaluation—including maternal vital signs, fetal heart rate monitoring, cervical examination, and possibly transvaginal ultrasound or fetal fibronectin testing—is essential to distinguish benign uterine activity from pathological processes.

Patients experiencing frequent contractions in late pregnancy should contact their obstetric provider without delay. Early recognition and appropriate management help safeguard both maternal and fetal well-being and reduce risks associated with preterm birth or complications of labor onset.