(1) the systolic pressure or the peak arterial pressure at the onset of the cardiac cycle and
(2) the diastolic pressure or lowest pressure representing the resting phase of the cardiac cycle.
Normal values vary among people. In the US for example, the average is 120 mHg for the systolic pressure and 80 mmHg for the diastolic pressure.
Low Blood Pressure a Trick or Treat?
Persistent higher (hypertension) and lower (hypotension) than the average blood pressure value is a sign of a potentially serious condition. However, unlike hypertension, hypotension does not normally pose any immediate risks.
In fact, the value for low blood pressure is very arbitrary what could be low for some is normal for others. It was even found out that most people with lower blood pressure are less likely to have cardiovascular-related diseases. It is the onset of the symptoms that makes low blood pressure quite alarming. However, it cannot be discounted that severe cases may have serious implications on the heart, endocrine system, and/or the brain.
Some of the symptoms for low blood pressure include dizziness, fainting, blurred vision, fatigue, depression, among others. Pregnant women normally experience dizziness and fainting. Hypotension leads to low sources of oxygen in most of the vital organs of the body because of the inability of the heart to pump the required amount of blood to the other parts of the body. While it may not be that serious, medical help should be sought.
What Causes Low Blood Pressure among Pregnant Women?
Changes in the blood pressure amongst pregnant women brought about by the pregnancy usually occur in the beginning of the 24th week or in the onset of the second trimester.
The drop in the systolic pressure and diastolic pressure can be as much as 10 points and at most 15 points, respectively. At this time, a womans circulatory system has to rapidly expand to accommodate the blood requirements of the baby within her womb. This can only be resolved when the babys system has fully developed.
Furthermore, in most cases, low blood pressure among pregnant women is not permanent and life threatening because it can be easily remedied. Unlike hypertension, hypotension in itself is not treated but rather its cause. One most common example is dehydration, which can be resolved immediately by increasing sodium and water intake to promote hydration and water retention.
The expansion of the uterus due to the babys rapid growth puts pressure on the aorta and the vena cava that extends from the right leg to the heart. This is the reason why pregnant women particularly those in their 3rd trimester are asked to lie down on their side to avoid putting pressure on these arteries.
Another source of hypotension among pregnant women is the sudden rise from a sitting position, lying down, or squatting. This happens because standing up rapidly makes the blood from the brain to also drain out of the brain rapidly due to gravity. This can be prevented by getting up slowly from a low-lying position.
Does Low Blood Pressure Have an Effect to Perinatal Outcomes?
Perinatal is period at the end of the 20th to 28th week of pregnancy and about a month post delivery. This period is characterized by rapid physical development of the fetus. Hence, health problems contracted by pregnant women at this stage may have a potential effect on the fetus.
Studies made in 2001 by Dr. Zhang and Dr. Klebanoff, in their article “Low Blood Pressure During Pregnancy and Poor Perinatal Outcomes: An Obstetric Paradox“, proved that low blood pressure during the perinatal stage does not in itself affect the pregnancy or the child itself. They found out that most cases of miscarriages or pre-term labor was due to other conditions that the pregnant women already had (i.e., smoking and drinking even while pregnant, among others).
They were also able to prove in their study that fetal growth is also unaffected by low blood pressure nor would it have any effect on the intelligence of the child.
Another study was conducted in 2004 by the team of Dr. Philips Steer of Academic Department of Obstetrics and Gynaecology, Imperial College London. It also investigated the effect of low diastolic levels to the perinatal outcomes. This study showed that the optimal diastolic pressure to achieve the maximum birth weight is between 70 to 80 mmHg. Lower birth rates are observed in diastolic levels higher and lower than the said range.
They also found that the optimal diastolic blood pressure is about 80mmHg and found about 11% perinatal deaths not equivalent to this rate. It was also observed that most of the 11% deaths were attributed to lower diastolic rates.