Low Blood Pressure During Pregnancy

Introduction

Blood pressure is the force by which blood circulates in the arteries, and consists of two subtypes: systolic and diastolic. Both are needed to contribute to the patient's overall blood pressure measurement. A systolic pressure of less than 120 and a diastolic pressure of less than 80 are known to be the optimum levels for healthy functioning of the body. 

Healthy blood pressure during pregnancy is within the range stated above. If there is a deviation from this point, serious complications, such as preeclampsia, may develop.¹ Hence, it is important to track and manage blood pressure throughout pregnancy. Low blood pressure can occur due to hormonal changes and fluctuations, and the fact that nutrients are being absorbed by both the baby and the mother.

Effect of pressure during pregnancy

Low blood pressure (also known as hypotension) is categorised if your reading is 90/60 mmHg or lower. This can occur due to excess secretion of the hormone progesterone, which causes blood vessels to dilate and expands the circulatory system in late-stage pregnancy.² 

Symptoms of low blood pressure

Symptoms include nausea, dizziness, fainting, rapid heartbeat, weakness, fatigue, and sleeplessness. Some cases can also include dehydration, anaemia, internal bleeding, heart conditions, nutritional deficiencies, feelings of constant thirst, and allergic reactions.³ Excess protein in the urine, severe headaches, blurred vision, nausea and vomiting, shortness of breath, and decreased urination are also all symptoms of hypertension.⁴

Dangers of low blood pressure during pregnancy

It is very common for those who are pregnant to experience a drop during the first 2 weeks.¹³ For a healthy individual, most of the symptoms will disappear in the last trimester. Severe nausea or vomiting can also occur.⁵ 

Can low blood pressure be harmful to the baby?

For the most part, low blood pressure does not cause much harm, but when the pressure falls below a certain point, both the mother and the foetus will be affected. Food supply to the foetus is reduced, which may cause brain death or the child being stillborn.⁶ In some cases, it causes organ failure,  changes to the cardiovascular system, and increased prostaglandin activity, which in turn increases angiotensin activity. 

Vasodilation occurs, which further lowers blood pressure and causes high ventricular attacks.¹⁰ In certain cases, low blood pressure causes preeclampsia and eclampsia which indicates blindness; while regional blood flow blocks cause pregnancy-induced hypertension.¹⁴ 

Some women experience issues of low blood pressure even before pregnancy. Diagnosis can be done using echocardiography on infants and is treated by prescribing drugs dopamine and vasopressin. Certain immune system conditions are also caused by low blood pressure. 

Research studies show that increased birth weight is directly associated with low blood pressure, but underweight babies have little connection. Extremely low birth weight, under 1000gms, due to blood pressure may cause certain neurological conditions in infants. Babies with symptomatic hypotension have delayed movement development, hearing loss, and, in some cases, even serious complications that can lead to death. 

Infants that are born with low blood pressure are more likely to have symptomatic hypotension. It has been recognized that all these symptoms are due to perfusion pressure at the cerebrum. Hearing loss is caused by ischemic nerves causing injury at the cochleae, associated with the auditory nerve. Infants may experience cardiovascular impacts, for which steroids can be prescribed. The treatment has its own potential side effects, including hyperglycemia and hypotension in adulthood. Seizures in infants are very common, and magnesium sulphate is given to reduce them, which causes poor growth and prematurity. 

Other factors that can contribute to low blood pressure

There are some other factors that contribute to low blood pressure. Anaemia during pregnancy is associated with hemorrhagic tension, which causes uteroplacental perfusion and affects the growth of the placenta. In most instances, pregnancy hypotension is temporary, consisting of postural hypotension and supine hypotension. 

• Postural hypotension is when blood pressure remains low after sitting or whilst in a standing position as blood flow has a delayed arrival to the brain. 
• Supine hypotension causes tensions in the vena porta, leading to expansion of the uterus around the second and third trimester. 

Other causes that lead to low blood pressure during pregnancy are dehydration, which causes dizziness and accumulation of blood in the legs.⁹ Certain vitamin deficiencies such as B12 and folic acid may also be contributing factors. 

Diagnosis

Low blood pressure can be diagnosed in several ways. Your health care provider will assess the prevalence of hypertension using an electrocardiogram as well as physical and stress tests.¹¹ There are certain ways in which you can handle blood pressure at home. There are easily available at-home testing kits that give you an accurate reading of your blood pressure. 

Tips on dealing with low blood pressure during pregnancy

Natural remedies, such as drinking large amounts of liquid, exercising regularly, eating small and low-carb meals, and increasing vitamin K intake have been shown to be effective for maintaining blood pressure. Eating red meat could help resolve hypertensive symptoms, however eating it when experiencing low blood pressure could increase blood flow and negatively impact long-term health. If the dizziness or nausea continues, speak to your GP about potential treatments. Intaking a good amount of vitamins could be helpful. 

Increased salt usage is generally used as a preventative measure, along with wearing compressible stockings.¹⁶ Certain foods should not be consumed by someone who suffers from low blood pressure, such as foods rich in carbohydrates, bread, and alcohol. Dark chocolate should also be completely avoided. People with postprandial hypotension should rest for an hour after eating to prevent cramps and remain hydrated in warm weather. Agitation may also be observed in those who are affected. Certain medications are used to treat low blood pressure, such as steroids, and fluro corticosteroids.17

Postpartum blood pressure

Postpartum high blood pressure is a condition that is caused in women right after childbirth, which can lead to stroke and even death. If it lasts more than 12 weeks, then make an appointment with your GP. There isn’t much research on postpartum eclampsia, however it is understood that certain complications may occur, including heart diseases and pulmonary oedema, stroke, HELLP syndrome, and diabetes.⁸ This also may include temporary loss of vision. Hemolysis causes the destruction of red blood cells, elevated liver enzymes, and low platelet count which leads to bleeding and haemorrhage. Diagnosis of postpartum blood pressure can be done using blood pressure and urine samples. 

Treatment of postpartum preeclampsia consists of taking magnesium sulphate before delivery. Beta blockers may help to reduce heart rate.¹⁵ Diuretics can be used to help reduce excess blood pressure in the body. Women who breastfeed their babies, may experience more intense symptoms. Hemolysis, placenta abruption, and poor blood flow to the placenta are some of the complications of preeclampsia. Antihypertensives, antifoulants, and corticosteroids are helpful to increase blood pressure after childbirth.¹⁸

Summary

Low blood pressure is very common among pregnant women in their last trimester. Symptoms such as dizziness, fatigue, rapid heartbeat, preeclampsia, and heart disease may occur. This is usually due to ventricular contractions and expansion of the uterus. 

Certain immune distortions also cause low blood pressure. Usually, this lasts for 12 weeks and goes after pregnancy. While this is a common experience, if symptoms exceed a duration of 12 weeks, then you should contact your GP to discuss a treatment plan. Symptoms are used as the first point of investigation for diagnosis. 

The foetus is equally impacted by low blood pressure and experiences a reduction in  blood and food supply. Infants which are born from a mother with low blood pressure tend to have delayed motor movements, difficulty speaking and hearing loss.¹⁴ They often have a low birth weight of less than 1000gms. Certain steroids like corticosteroids, vasopressin, and fluro corticoids can be used as treatment. Home remedies include taking ample amounts of rest, staying hydrated, taking proper medications, and avoiding stressful movements.