Does Pregnancy Lower Blood Pressure? 

During pregnancy, a woman’s body undergoes significant physiological changes to support the growing foetus, and one of the most common shifts occurs within the cardiovascular system. It is very frequent for blood pressure to decrease, particularly during the first and second trimesters, as the circulatory system expands and hormonal levels fluctuate. This article provides a clear, factual overview of why these changes happen, what symptoms you might expect, and how to differentiate between a normal pregnancy response and signs that require clinical attention. You will also learn about safe management strategies and the importance of regular monitoring throughout your pregnancy journey. 

What We’ll Discuss in This Article 

• The physiological reasons why blood pressure typically drops during pregnancy. 

• When these changes usually occur within the three trimesters. 

• Common symptoms of pregnancy-related hypotension, such as dizziness. 

• The role of hormonal shifts and expanded blood volume. 

• Specific triggers that can cause sudden dips in pressure for expectant mothers. 

• How to differentiate between normal low pressure and pre-eclampsia risks. 

• Practical steps for maintaining stable pressure and safety guidance. 

Does Pregnancy Lower Blood Pressure? 

Yes, pregnancy often lowers blood pressure because the circulatory system expands rapidly to provide blood flow to the foetus. Hormonal changes, specifically an increase in progesterone, cause the walls of the blood vessels to relax and widen (vasodilation). This reduced resistance, combined with the fact that blood must now fill a much larger network of vessels, naturally leads to a decrease in systemic blood pressure, which typically reaches its lowest point during the second trimester. 

During the first 24 weeks of pregnancy, it is common for the systolic pressure (the top number) to drop by 5 to 10mmHg and the diastolic pressure (the bottom number) to drop by as much as 15mmHg. For most women, these changes are a normal part of a healthy pregnancy and do not cause significant issues. The body usually begins to adjust, and blood pressure typically returns to pre-pregnancy levels during the third trimester as blood volume continues to increase and the body prepares for labour. 

• Blood pressure usually starts to fall in the first trimester. 

• The lowest readings are often recorded between weeks 18 and 24. 

• Widening blood vessels are the primary cause of this natural drop. 

Causes of Low Blood Pressure in Pregnancy 

The primary causes of low blood pressure during pregnancy are linked to the massive expansion of the mother’s blood vessels and the diversion of blood flow toward the uterus. As the placenta develops, it requires a significant and constant supply of blood, which changes the way pressure is distributed throughout the body. Additionally, the increase in pregnancy hormones acts as a natural vasodilator, causing the arteries to remain more relaxed than they would be in a non-pregnant state. 

While the body eventually increases its total blood volume by about 45 per cent to compensate, this process takes time. During the early and middle stages of pregnancy, the expansion of the ‘pipes’ (the blood vessels) often outpaces the production of the ‘fluid’ (the blood), resulting in a temporary period of hypotension. Clinical factors that can exaggerate this drop include carrying multiples (twins or triplets), being dehydrated, or having certain underlying heart conditions that make it harder for the body to adjust to the increased demand. 

• Hormonal Changes: Higher progesterone levels relax the muscular walls of the blood vessels. 

• Placental Demand: A large volume of blood is redirected to support foetal growth. 

• Expanded Circulatory System: The network of vessels grows significantly to accommodate the placenta. 

• Dehydration: Morning sickness or poor fluid intake can reduce total blood volume further. 

Triggers for Symptomatic Drops 

Expectant mothers may find that certain physical triggers cause their blood pressure to drop sharply, leading to sudden symptoms like lightheadedness or feeling faint. Standing up too quickly is a common trigger, as gravity pulls blood away from the brain more easily when vessels are relaxed. Another specific trigger in later pregnancy is lying flat on the back (the supine position), which can cause the heavy uterus to press against the inferior vena cava, a major vein returning blood to the heart. 

Triggers to be mindful of during pregnancy include: 

• Postural Changes: Moving from a sitting or lying position to standing too fast. 

• Prolonged Standing: Especially in warm environments, which can cause blood to pool in the legs. 

• Hot Baths or Showers: Heat further dilates blood vessels, increasing the risk of a dizzy spell. 

• Lying on the Back: Can reduce blood return to the heart in the second and third trimesters. 

• Large Meals: Blood is diverted to the gut for digestion, potentially lowering systemic pressure. 

Differentiation: Low Pressure vs. High Pressure Risks 

It is important to differentiate between the normal, healthy drop in blood pressure seen in mid-pregnancy and the onset of high blood pressure conditions like gestational hypertension or pre-eclampsia. While low blood pressure is generally harmless and causes dizziness, high blood pressure in pregnancy is a serious clinical concern that requires urgent monitoring. Understanding the difference between ‘feeling faint’ and ‘feeling unwell’ with specific red-flag signs is vital for maternal safety. 

Feature	Pregnancy-Related Hypotension	Pre-eclampsia (High BP Risk)
Typical Timing	Most common in the second trimester.	Usually occurs after 20 weeks.
Key Symptoms	Dizziness, blurred vision when standing.	Severe headache, swelling of hands/face.
Vision Changes	Brief ‘stars’ or blurring that passes.	Persistent blurring or flashing lights.
Associated Pain	Minimal or linked to hunger/thirst.	Pain just below the ribs (upper right).

Conclusion 

Low blood pressure is a very common and usually normal feature of pregnancy, reflecting the incredible adaptations your body makes to support a new life. While the symptoms of dizziness and fatigue can be inconvenient, they are typically manageable by moving slowly, staying well-hydrated, and avoiding lying flat on your back. It is essential to attend all your antenatal appointments so that your blood pressure can be monitored regularly, ensuring that these natural shifts remain within a healthy range for both you and your baby. 

If you experience severe, sudden, or worsening symptoms, call 999 immediately. 

You may find our free Pregnancy Due Date Calculator helpful for understanding or monitoring your symptoms. 

Authority Snapshot (E-E-A-T Block) 

This article was written by Dr. Rebecca Fernandez, a UK-trained physician with an MBBS and extensive experience in gynecology, cardiology, and emergency medicine. Dr. Fernandez has managed critically ill patients and provided comprehensive care for expectant mothers across diverse clinical settings, ensuring this guide provides accurate and safe health information. This content is designed to align with current UK medical frameworks to help the public navigate cardiovascular changes during pregnancy safely.