Blood Pressure in Pregnancy

I was recently asked some questions regarding blood pressure during pregnancy by my colleagues at Physiquality. In preparing material, I wrote this blog, which includes very basic clinical information and explanations about this topic.

What is the normal range for blood pressure for pregnant women? What readings would fall under high blood pressure?

Blood Pressure (BP) in pregnancy is a complex topic.

First, we need to know: What are the classifications of BP?

The chart below is from the evidence-based 2014 Guidelines of the American Heart Association and the National Heart, Blood and Lung Institute of the NIH. The first number is Systolic BP or during the heart beat. The second number is Diastolic BP or between beats. These numbers are relevant for women of childbearing age.

  • Normal                        <120 mm Hg and <80 mm Hg
  • Pre-hypertensive          120-139 or 80-89
  • High BP Stage 1            140-159 or 90-95
  • High BP Stage 2            ≥ 160 or ≥ 10

Why does low BP (hypotension) occur in a healthy pregnancy?

A healthy pregnant woman with normal BP and no cardiovascular or immune system complications, will have pregnancy BP lower than her non-pregnant BP due to increased progesterone relaxing her vasculature. To create the placental and uterine blood flow, blood volume (V) expands rapidly increasing by around 40%, but stroke volume increases less, so beats per minute (pulse) may increase, systolic BP may drop 5 mm Hg and diastolic may drop 10-15 mm Hg. If V is not adequate with this relaxed vasculature, BP may drop even lower. To help maintain normal BP, women are encouraged to drink sufficient water (about 8 glasses/day) and eat enough protein (about 20-25% of daily intake) to produce a blood volume that will sustain an adequate BP. Other more severe conditions – often genetic – may also be relevant, such as postural orthostatic tachycardia syndrome.

Other causes of hypotension include lying still on the back with legs extended for long periods of time after the first trimester. The weight of the uterus impinges on the vena cava returning blood to the heart, thus reducing BP and blood flow to the uterus and placenta. Also, standing for long periods of time with a minimum of motion, as happens with teachers, cashiers, line workers and nurses in the second half of pregnancy when increasing relaxin and elastin cause further softening of vasculature. This results in difficulty returning blood from the lower limbs and reducing blood flow to the uterus and placenta.

What are hypertensive disorders of pregnancy?

According to the National High Blood Pressure Education Working Group on High Blood Pressure in Pregnancy, hypertensive disorders of pregnancy are presently classified into four categories:

  • Chronic hypertension (pre-existing)
  • Preeclampsia-eclampsia
  • Preeclampsia superimposed on chronic hypertension
  • Gestational hypertension

[The Society of Obstetricians and Gynecologists of Canada categorize these disorders as pre-existing or gestational, with the addition of preeclampsia to either category.]

Chronic hypertension is BP >140/90 prior to pregnancy or before 20 weeks. New onset of high BP after 20 weeks may indicate preeclampsia (PE), which requires further consideration. PE involves other symptoms and organs. It occurs in about 5% of all pregnancies, 10% of first pregnancies and 20-25% of women with a history of chronic hypertension. It is a serious disorder and major cause of adverse maternal and fetal outcomes, including strokes, seizures and restricted fetal growth and development.

The underlying pathogenesis of preeclampsia-ecclampsia is not yet fully understood, but is a fundamental dysfunction of the placenta leading to endothelial dysfunction and vasospasm. Possible causes include pre-existing endothelial dysfunction, metabolic dysfunction, auto-immune responses and infection. It is likely that the placenta is affected very early on, during implantation, trophoblast invasion of the uterus and opening of the spiral arteries to form the blood pool on the maternal side of the placental circulation.

Gestational hypertension is the onset of BP >140/90 after 20 weeks without other features of preeclampsia. About 1/3 of these women develop preeclampsia. Gestational hypertension is highly associated with hypertensive disorders later in life. Diabetes can also be a factor associated with hypertension.

Whenever a woman has elevated BP in pregnancy, she needs to be evaluated and have a follow up course of observation and treatment. At its most severe, a hypertensive disorder can affect all the body’s organs and systems, and can be fatal.

What can pregnant women do (diet, exercise, healthy habits) to keep their blood pressure within a normal range?

Some risk factors for hypotension or hypertensive disorders of pregnancy are inherited, others are a consequence of behavior, and many are a combination.

What can a woman do before pregnancy?

Because the events that pre-dispose a woman to hypertensive disorders may occur before she knows she is pregnant, some efforts at prevention may be helpful in the six months to a year prior to pregnancy. Preparing for the implantation period by maintaining optimal health and fitness is likely the most helpful behavior. Cardiovascular or aerobic fitness, which prevents or reduces the severity of endothelial dysfunction is highly valuable. An adequate daily nutrient intake along with sufficient water, and maintaining a BMI <25 are important factors. Women with elevated blood pressure should discuss with their care provider the balance of sodium and potassium intake, along with the total allowable amounts.

Avoiding infections or illness around the time of conception may be a factor. Hypertensive disorders are mediated by inflammation. Unfortunately, another factor may be the maternal immune response to the fetal DNA. This may also be dependent on combined maternal/paternal immune system responses.

What can a woman do once she is pregnant?

Once a woman is pregnant, maintaining optimal health and fitness continue to be important. Even if there are pre-disposing factors for disorders, she may be able to reduce the severity by staying fit, well nourished and well rested. A balanced and colorful diet, along with avoidance of alcohol, drugs and unsafe behaviors are critical.

The ability to achieve the Relaxation Response, meditation, deep breathing and hypnosis are valuable for acute BP reduction. Each of these skills is mediated by the parasympathetic nervous system response (or alpha brain rhythm) and mitigates the effects of stress on a temporary basis. Cardiovascular or aerobic fitness is effective for long-term BP reduction, as well as cardiovascular health.

Resting on the left side maximizes circulation and – if possible – finding 15 or 20 minutes to rest this way during the day is beneficial, especially if a woman’s work involves standing for long periods of time. Avoiding lying on the back or standing for long periods of time is advisable. Finding a community of support for having a healthy pregnancy can be a great asset, as well.

Pregnancy Pathway, Pregnancy – Maternal Immunological Response

Today: Maternal Immunological Response…or…the Mother/Fetus Dance!

Maternal Immune Response During Pregnancy

Maternal Immune Response During Pregnancy

Back to work! Thank you for your forebearance while we wrote a chapter for a nursing textbook!

During the course of pregnancy, the mother/fetus dance is ongoing. The maternal immune system and the trophoblast cells continue to influence each other even beyond the implantation.

Because the mother’s immune response modulates near the start of each trimester, the fetus is affected to some degree and mounts a response, as well. For a long time it was thought that maternal and fetal DNA material was not exchanged across the placental membrane, however recent findings indicate that there is some exchange of material. Thus, we all carry some portion of our mother’s DNA and our mother carries some of ours.

What is the impact of this chimeric effect? It depends on how well our DNA gets along!

How does this affect the fetus in utero? The fetus may be affected by clotting issues. Depending on maternal health status s/he may be subject to a stronger or weaker immune system.

How does this affect the mother? Women are more likely than men to develop autoimmune disorders (pregnancy playing a role here), and those who bear male offspring are more likely than those who only have girls to have these disorders.

The maternal/fetal dance goes on….

Be Prepared for Birth!

Be Prepared for Birth!

Pregnancy Pathway, Conception – Prior Sperm Exposure

Today:  Sperm!!!

For complete graphic, see Feb. 5 or 23 post.

The mother's prior sperm exposure can affect her pregnancy.

The mother's prior sperm exposure can affect her pregnancy.

Not every sperm is your friend! Sperm exposure – like so many exposures – affects our immune system. Women who have babies with more than one father may be at risk for disorders of pregnancy because the challenges to their immune system have been extensive. And, very young women who become pregnant are at increased risk of some disorders because they have had very little exposure to sperm.

In addition, women who have primarily and extensively used barrier methods of contraception may be at risk for disorders for reasons similar to young women with little exposure. Unlike women whose immune system has had too much challenge due to pregnancies by several men, women with little exposure may not have a strong defense against foreign DNA. Please do not take this as a reason to not use a condom – one of the barrier methods along with a diaphragm and cervical cap. Rather, if you use a barrier method of contraception, keep in mind that your body’s adjustment to pregnancy may take time.

For more information on barrier methods, to go the American College of Obstetricians and Gynecologists’ online pamphlet: ACOG Pamphlet on Barrier Contracetption.

Another way sperm can affect the pregnancy is that the combination of the mother’s and father’s natural immune responses may be strong against the trophoblast implantation. This is not something  you can know ahead of time. Also, women are eight times more likely than men to develop autoimmune disorders. One reason may be the prenatal exposure to foreign DNA encountered in pregnancy.

Keep in mind that by getting good prenatal care, exercise, sufficient rest, stress managment and healthy nutrition, you do all within your power to have a healthy pregnancy. Your health care provider will determine your risk factors that may affect pregnancy outcome and treat you in an appropriate manner.

Moms and babies enjoy exercise together!

Moms and babies enjoy exercise together!

Once your baby comes, there will be time to maximize health for both of you. Exercising together is great fun!

Getting there may require some patience, but the reward is well worth it.

When you are looking around for sperm, use your head. The same behavior that protects you from infections you never want to get, protects you from sperm you don’t really want to meet. When the time comes to adopt some sperm, find out about it’s credentials!

Pregnancy Pathway, Preconditions – Genetics

Please refer to February 5 entry for complete graphic. The Precondition we will discuss today is Genetics.

bubblus_preconditions_-_genetics

There are genetic factors totally outside your control that determine things as simple as your offspring’s hair or eye color, how the earlobe attaches to the side of the head and whether or not s/he can roll the tongue. More complex things, such as a predisposition to types of cancers, bleeding disorders or various other diseases, also have a genetic basis.

Because the male contributes the sex of the offspring, once conception happens, the sex off the fetus is determined — at least genetically. But, it turns out not everything genetic is set in stone. In utero, hormone exposures may affect how male and female characteristics develop, so that some girls will be very girlie, some will be tomboys, and some may be gay. A similar effect will influence how boys develop.

Genetic, environmental and behavioral preconditions can be  intertwined. Environmental factors can alter genes, causing them to express proteins that would otherwise be dormant. Likewise, our behavior affects some of our genes. If we have a family propensity for heart disease, but we eat a healthy diet, exercise and avoid risky behaviors, we alter the impact of our genetic code.

Keep in mind that some things will be completely determined by genes. It is not reasonable to hope, for example, that our offspring will be 6’5″ if both parents are short (or vice versa). If the mother has “thrifty genes” — that is, genes that make it easy for her to gain weight — she may well do so during pregnancy, even if she follows a reasonably healthy lifestyle. If the immune systems of both parents have some similarities, it may affect the maternal immune response to the implanting trophoblast cells, thus affecting the placenta and, indeed, the entire pregnancy.

So, how do we advise people who are thinking of pregnancy to prepare themselves for a healthy pregnancy genetically? Surely, to determine all the potential genetic possibilities is not feasible or affordable at this point. Maybe in another century! But, we can know some factors:  Is there sickle cell anemia in both families? Is there a Mediterranean type of sickle cell disorder? What about clotting factors or differences in Rh? What about diseases or disorders that are not common, like ALS? These are things that potential parents may want to discuss.

Like so much of life, we can’t know everything. There are no guarantees. There is a lot to be learned still about human genes and how they work.

This blog has at its heart the notion that physical activity has tremendous benefits for mother and offspring…and for partners, too. How does the genetic component affect this? First, preconception fitness lowers some risk factors for mothers and babies. Second, each mother’s genes will make it easier or more difficult for her to enjoy or benefit from the activity of exercise. We appreciate this and encourage young moms-to-be to find something enjoyable that you like doing and find people or situations that support you in being active now before you become pregnant.

If you need assistance or advice, please go to http://www.dancingthrupregnancy.com (use the BlogRoll)

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