According to the March of Dimes, between 65 million and 75 million women are of child
bearing age at any given time in the US. Furthermore, there are approximately 2.25 million
women that are currently pregnant at any given time. This averages out to about 450,000
pregnant women per state. Pregnancy related changes place a very large demand on a
woman’s body. Almost every organ system experiences some degree of change at one point
during this period. These changes will often either uncover undiagnosed medical conditions or
can make pre-existing conditions worse. Today we are going to look at the two body systems
that are most affected.
The cardiovascular system is most extensively affected after a woman becomes
pregnant. Fluid volume (primarily plasma) increases by 40-50% while the red blood cell count
only increases by around 33%. This often leads to a pseudo-anemic state. Hematocrit levels
decrease, this decrease peaks around 32-34 weeks gestation. Albumin, the most abundant
protein in human blood, helps to maintain fluid pressure of the blood. It aids in preventing fluid
from leaking out of the vascular system and into the extravascular space. As albumin levels
decrease during the gestational period, the pregnant female often experiences generalized
edema that is not directly related to fluid overload. Hypercoagulability can cause them to be
more prone to blood clots as the fibrinogen levels increase by 2-3 times her normal level.
Elevated Pt and PTT levels are not unusual during pregnancy. Hormonal changes will decrease
vascular resistance by causing systemic vasodilation. This often equates to an overall systolic
blood pressure decrease of 5-10 mm/Hg and a diastolic decrease of 10-15 mm/Hg. The blood
pressure decrease tends to peak during the second trimester and will often partially resolve by
30-36 weeks gestation. This lowering of blood pressure can often be misinterpreted as or
mask a hypotensive state. It is not unusual to see 12 lead ECG changes due to the fact the
gravid uterus pushes up on the diaphragm and this can elevate the apex (ventricles) of the
heart. A left axis deviation is often a benign finding due to this change. Third heart sounds and
an average increase in pulse rate of 10-15 beats per minute is not unusual.
The respiratory system is probably the second most severely affected organ system.
Normal non-pregnant minute ventilation (Mve) is approximately 4-6 lpm. Do to the gestational
changes necessary to support fetal development, this number increases to around 6-9 lpm.
Remember the formula for ventilatory minute ventilation is Mve=Tidal Volume x Ventilation
Rate. Increased minute ventilation is often due to an overall increase in tidal volume, primarily
in the first and second trimesters. In the third trimester, the gravid uterus often will elevate the
diaphragm and necessitate an increase in ventilatory rate to maintain minute ventilation. This
can often cause a relative respiratory alkalosis. Arterial Blood Gases will tend to trend towards
a lower PaC02 level due to this increased breathing rate. Hormonal changes will lead to
capillary engorgement and generalized airway swelling that can complicate airway
management. Mallampati scores of 3-4 are not unusual so a high index of suspicion for a
difficult airway have to be anticipated. These same hormonal changes that relax the body’s
smooth muscle will also affect the gastroesophageal sphincter (cardiac sphincter). This
smooth muscle relaxation in conduction with an elevation of the diaphragm can lead to an
increased probability of vomiting during invasive and noninvasive airway maneuvers.
The anatomic and physiologic changes that occur during pregnancy can be significant
and often can either uncover or exacerbate underlying or pre-existing medical conditions.
Health care providers that are familiar with these gestational changes can be better prepared to
manage these unique patients. A high index of suspicion aids the provider with staying ahead
and anticipating changes while treating the pregnant female. While most pregnancies progress
to term and eventual delivery, it is important to identify and respect the changes that occur in
the human body during this gestational period. Being aware of these changes allow the
provider to provide the best care po