Low blood pressure during pregnancy is common and usually harmless. In a typical pregnancy, blood pressure gradually drops from the first trimester onward, reaching its lowest point around 28 weeks before slowly climbing back toward pre-pregnancy levels. This dip is a normal part of how your body adapts to support a growing baby, but in some cases it can cause uncomfortable symptoms or, rarely, affect fetal growth.
Why Blood Pressure Drops During Pregnancy
Your cardiovascular system undergoes dramatic changes almost immediately after conception. Blood vessels throughout your body begin to relax and widen as early as five weeks, well before the placenta is fully formed. By the middle of the second trimester, the resistance in your blood vessels drops by 35% to 40% compared to pre-pregnancy levels. That’s a massive shift, and it’s the primary reason blood pressure falls.
Several hormones drive this process. Estrogen and progesterone both promote blood vessel relaxation, and their levels rise substantially throughout pregnancy. A lesser-known hormone called relaxin, produced by the ovaries, also acts on small blood vessels to reduce resistance. Research from the American Heart Association has shown that higher levels of relaxin and progesterone early in pregnancy are linked to lower blood pressure readings in the second and third trimesters.
At the same time, your total blood volume increases by roughly 45%, with plasma volume expanding faster than red blood cell production. This expansion creates what’s sometimes called a “physiological anemia” from dilution. Your body compensates by activating systems that retain salt and water, but progesterone partly counteracts that retention. The net result is a cardiovascular system that’s working harder to fill a much larger network of relaxed blood vessels, which naturally lowers pressure.
What Low Blood Pressure Feels Like
Many pregnant people with low blood pressure feel nothing unusual at all. When symptoms do appear, the most common ones are:
- Dizziness or lightheadedness, especially when standing up quickly
- Fatigue that feels disproportionate to your activity level
- Fainting or near-fainting episodes
- Blurred vision or difficulty focusing
- Nausea that worsens with position changes
These symptoms tend to be most noticeable during the second trimester, when blood pressure is at its lowest. They often hit hardest when you’ve been standing for a long time, when you’re dehydrated, or when you get up from sitting or lying down. If you feel faint, sitting or lying down on your left side usually resolves it within minutes.
Supine Hypotensive Syndrome
Later in pregnancy, lying flat on your back can trigger a specific type of low blood pressure called supine hypotensive syndrome. The growing uterus compresses the large vein (the inferior vena cava) that returns blood from your lower body to your heart. With less blood flowing back, your blood pressure can drop by 15 to 30 points within minutes. Symptoms include sudden dizziness, pallor, sweating, nausea, and a racing heart.
This tends to become relevant after about 24 weeks of pregnancy, when the uterus is large enough to put meaningful pressure on that vein. The fix is simple: rolling onto your left side shifts the uterus off the vein, and symptoms typically resolve quickly. This is one reason you’ll often hear the recommendation to sleep on your side rather than your back during the second half of pregnancy.
Risks to the Baby
A temporary dip in blood pressure is not a concern for fetal health. Persistent low blood pressure, however, may affect how well blood flows to the placenta. Research published in the European Journal of Obstetrics found that women with persistently low blood pressure were significantly more likely to have smaller-than-expected babies. In that study, 21.3% of women with persistent hypotension had small-for-gestational-age newborns, compared to 11.6% of women without it. After adjusting for other factors, persistent low blood pressure raised the odds of a smaller baby by about 65%.
The key word is “persistent.” Women whose blood pressure dipped temporarily and then returned to normal range did not have the same increased risk. This distinction matters because it means the routine, mid-pregnancy blood pressure drop that nearly all pregnant people experience is not the same thing as the chronic low readings that warrant closer monitoring.
Managing Low Blood Pressure
Most cases don’t require medical treatment. The goal is to minimize symptoms and prevent fainting, which carries its own injury risks. A few practical strategies help:
Stay hydrated consistently. Aiming for roughly 80 to 100 milliliters of fluid per hour (water, fruit juice, coconut water) helps maintain blood volume. Dehydration makes low blood pressure worse, and pregnancy increases your fluid needs significantly.
Increase salt intake cautiously. Your doctor may suggest adding a bit more salt to your diet to help your body retain fluid. This is one of the few situations where extra salt can be beneficial, but the amount matters, so it’s worth discussing specifics with your provider rather than salting aggressively on your own.
Move slowly when changing positions. Standing up quickly is one of the most reliable triggers for dizziness. Take a few seconds to sit at the edge of the bed before standing, and pause if you feel lightheaded.
Consider compression stockings. Knee-high compression socks help push blood back toward your heart and reduce pooling in your legs. They’re especially useful if you stand for long periods during the day.
Avoid long periods on your back after 24 weeks. Side-lying, particularly on the left, keeps blood flowing freely through that major vein.
Warning Signs That Need Attention
Occasional lightheadedness is expected, but certain patterns signal something more serious. Ongoing dizziness that lasts for days or keeps returning, fainting with no memory of what happened, vision changes like flashing lights or blind spots, or chest pain with a rapid heartbeat all warrant prompt medical evaluation. In early pregnancy, fainting or severe dizziness can occasionally indicate an ectopic pregnancy, which needs immediate assessment.
Blood pressure is checked at every prenatal visit for good reason. If your readings are consistently low and you’re experiencing symptoms, your provider can track trends over time and monitor your baby’s growth to catch any issues early. For most pregnancies, low blood pressure is simply your body doing exactly what it’s designed to do: opening up to nourish a new life.