It is quite common to have low blood pressure while pregnant due to the numerous body changes occurring at this period. Most women begin to experience a drop in their BP early in the first trimester with the middle of the second trimester often marking the point when the blood pressure is lowest . It does not generally lead to any adverse outcome, but severe cases may be dangerous for both the mother and baby.
What is considered low blood pressure during pregnancy?
The systolic (the top number) blood pressure reading ranging around 120 and the diastolic (the bottom number) pressure ranging around 80 is normal in a healthy individual. You are considered to have low blood pressure if either one of the readings is lower than normal . In most pregnant women, the systolic reading drops by 5-10 mmHg while the diastolic pressure drops about 10-15 mmHg. However, these readings may vary depending on your medical history and overall health .
Low Blood Pressure during Pregnancy Chart
|Severity Level ||Systolic Pressure||Diastolic Pressure|
|Borderline low BP||90 mmHg||60 mmHg|
|Low BP (mild)||60 mmHg||40 mmHg|
|Extremely low BP||50 mmHg||33 mmHg|
Is low blood pressure a sign of pregnancy?
Although commonly occurring in pregnant women, low BP is not a sign of pregnancy as it often remains asymptomatic in early first trimester.
What causes low blood pressure in pregnancy?
The rapid expansion in your blood volume for supplying enough oxygen and nutrients to the baby dilates the blood vessels, causing your blood pressure to drop . This is the most common cause of hypotension in pregnancy while other possible causes include carrying twins, a history of low BP or having underlying health issues like dehydration, anemia, endocrine problems and certain heart disorders . Other risk factors such as folic acid and/or vitamin B12 deficiency or being on a prolonged bed rest  may also be responsible. Administration of epidural often leads to sudden drop in blood pressure during labor .
What are the signs and symptoms of low blood pressure in pregnancy?
- Lightheadedness and dizziness (especially if you suddenly get up from a sitting or lying position) 
- Blurred vision
- Difficulty concentrating 
- Excessive thirst
- Pale, cold and clammy skin
- Weakness and fatigue
- Elevated heart rate
How to prevent low blood pressure in pregnancy?
- Including ample amounts of salt in your diet (excessive salt intake may affect the fetus or lead to high BP) 
- Drinking lots of fluids 
- Following a healthy balanced diet
- Taking your prenatal vitamins and folic acid supplements daily
Low Blood Pressure during Pregnancy Diagnosis
It is usually diagnosed during your regular prenatal checkup as your doctor routinely checks your BP for any abnormalities. Additional tests may be ordered to detect the exact causes:
- Blood Tests: Helps to determine whether you have diabetes, high blood sugar, anemia or any other blood disorder. A blood test also ensures the wellbeing of your baby.
- Ultrasound Tests: Allows your doctor to detect any irregularities in your heart’s structure and functioning .
Low Blood Pressure during Pregnancy Treatment and Management
Majority of cases do not need any treatment as the blood pressure starts to go up automatically during the third trimester, becoming normal after childbirth . Those refusing to resolve on their own may be managed at home with certain dietary and other health measures. Here are some tips for raising your BP levels and avoiding the symptoms:
- Lying on your left side as it increases the blood flow to your heart 
- Avoiding sudden rapid movements, especially when standing up
- Wearing support stockings (compression stockings) as the extra pressure provided by their tight-fitting elastic to your legs and abdomen helps to stimulate the blood circulation and increase your BP  (make sure to consult your physician to find out if they are suitable for you)
- Avoiding standing for extended periods of time (helps to prevent low BP due to miscommunication between the brain and heart) 
- Avoiding caffeine (especially at night) and alcohol
- Eating several small meals instead of three large ones (helps to avoid postprandial hypotension or low BP after eating) 
- Sitting still or lying down for a while after eating
- Avoiding lying on your back (especially after the 16th week) as this makes the uterus press on the principal blood vessels in your body, decreasing the blood flow to various organs and tissues 
- Avoiding strenuous exercises as your BP tends to drop lower after a strenuous workout session
Drugs and medications are not used unless there are serious symptoms or significant threat of complications for the mother or baby .
When to call the doctor?
Watch out for the following symptoms as they may indicate serious underlying problems when occurring along with low BP:
- Fainting feeling that worsens over time
- Severe headache
- Vision changes (blurred vision) 
- Excessive vomiting
- Shortness of breath
- Extremely high pulse rate
- Chest pain
- Numbness on just one side of your body
Low Blood Pressure and Pregnancy Possible Complications
Extremely low blood pressure may increase the risks of key organ damage in the mother . In some rare cases, it may also be associated with complications like ectopic pregnancy .
There is a lack of adequate research regarding the effects of maternal low BP on the baby. But, some studies show it to increase the risks of low birth weight and learning difficulties in the child as well as fetal death due to inadequate blood flow .
Low Blood Pressure ICD-9 and ICD-10 Code
The ICD-9 codes used for hypotension are 796.3 and 458  while its ICD-10 code is I95 .[ref]
- http://www.disabled-world.com/artman/publish/bloodpressurechart.shtml [/ref]