Low blood pressure during pregnancy

By trimester

Weeks 1–13

1st trimester

Early pregnancy circulation changes, vomiting, low fluid intake, or bleeding can contribute to dizziness with a low reading. Recurrent symptoms deserve a maternity-team review rather than assuming the reading is normal for pregnancy.

Weeks 14–27

2nd trimester

Blood vessels relax and vascular resistance falls as pregnancy progresses, which can contribute to lower readings around midpregnancy. Feeling well is reassuring, but dizziness, fainting, or a sudden change still needs clinical assessment rather than an assumption that the number is normal.

Weeks 28–birth

3rd trimester

Lying flat can compress major blood vessels and provoke symptoms in some people late in pregnancy. Roll onto your side if this happens and report persistent dizziness, fainting, bleeding, chest symptoms, or breathing difficulty promptly.

What does the evidence show for low blood pressure?

• A systematic review found that cardiac output rises during normal pregnancy while peripheral vascular resistance falls to a low point in early third trimester before increasing slightly, supporting a physiologic reason that blood pressure can run lower during pregnancy. 1
• Late-pregnancy symptoms while lying flat can result from aortocaval compression. A review describes positioning as central to this syndrome and notes that the usual degree of left tilt has been questioned as a universal standard. 2
• In a small magnetic-resonance study at 34 to 38 weeks, both symptomatic and asymptomatic participants had lower inferior vena cava flow and cardiac output when supine, while symptomatic participants had less compensatory azygos flow. The study measured maternal circulation, not fetal outcomes. 3
• Low blood pressure with no symptoms may need no specific action, but dizziness, fainting, weakness, blurred vision, or a sudden severe drop can accompany dehydration, blood loss, infection, an abnormal heart rhythm, or heart failure and warrants assessment based on severity. 4
• CDC urgent maternal warning signs include fainting, dizziness that persists or recurs over days, chest pain or a fast heartbeat, trouble breathing, inability to keep fluids down, and vaginal bleeding beyond spotting. 5

When should I call my provider about low blood pressure?

Call emergency services for fainting with failure to wake promptly, confusion, cold clammy skin, chest pain, trouble breathing, or a fast heartbeat. Contact the maternity team urgently for persistent or recurrent dizziness, a sudden marked drop, heavy vaginal bleeding, fever, severe vomiting with inability to keep fluids down, or symptoms after an injury or fall. If you are ever unsure which side of the line you are on, make the call. Obstetric teams handle these check-ins as routine, not as overreacting.