Physiological Changes in Pregnancy
Sandy Warner RNC – OB, MSN
Adaptations
• Nurses must understand the normal anatomical and physiological changes in pregnancy to recognize any deviation from normal.
• In addition to physical changes, there are also psychological changes that occur with pregnancy.
Body system alterations• Cardiovascular • Hematological• Respiratory• Genitourinary• Gastrointestinal• Immunological• Musculoskeletal• Endocrine
Cardiovascular
• Cardiovascular adaptation affects all organ systems.
• Cardiovascular anatomy and physiology changes to accommodate increasing maternal and fetal circulatory needs.
Heart
• Anatomic changes:
– Heart is enlarged, displaced upward and rotates to the left.
– PMI (point of maximal impulse) shifts to 4th
intercostal space and closer to the midclavicular line.
Heart sounds and rate:
• Audible splitting of S1 and S2; S 3 becomes audible.
• Benign systolic murmurs are common.
• Heart rate increases 15-20 beats as pregnancy progresses.
Cardiac Output
• Defined as the amount of blood pumped from the left ventricle into the aorta each minute.– (heart rate x stroke volume = CO)
• In pregnancy increased by 40% by 36-38 wks.
• Influenced by: • Blood volume• Stroke volume• Heart rate
TIME FRAME CARDIAC OUTPUT CHANGE
1st Trimester Increased 22% > pre-pregnancy values due to increased stroke volume
3rd Trimester Increased 30-50% > pre-pregnancy values due to increased heart rate and stroke
Labor Increased 12%-49% during 1st and 2nd stage due to shunting of blood from uterus to maternal circulation with ctxs and pushing
Blood Pressure
• Due to decreased systemic vascular resistance, blood pressure is lower at end
of 1st trimester and throughout 2nd, returning to baseline in 3rd trimester.
Also affected by renin-angiotensin-aldosterone system from kidneys.
Hematological Changes
• Increase in WBCs and RBCs.
• Increase blood volume for uterus, fetus and increased perfusion of other organs, especially kidneys.
• Increased plasma volume ratio to RBC volume leads to hemodilution.
Hematological changes cont.
• Hypercoagulation
• Decreased fibrinolytic activity
• Platelets remain normal or might decrease slightly
• Increased need for iron related to RBCs
Respiratory
• Anatomic changes:– Diaphragm elevation
– Chest expansion
– Capillary dilation early in pregnancy causes• Engorgement of entire tract from nares to bronchi• Voice changes
Respiratory
• Physiological changes:– Increased need for oxygen
– Improved oxygen delivery
– Hyperventilation
– Compensatory respiratory alkalosis
Genitourinary
• Kidneys – increase in size and GFR.
• Ureters – dilate and elongate, becoming compressed by uterus.
Bladder – tone decreases due to progesterone, becomes displaces as uterus grows.
Genitourinary
• Urine flow accumulates and slows.• Increased renal excretion of BUN,
creatinine and glucose.• Decreased serum BUN, creatinine and
glucose.• Decreased tubular reabsorption of
glucose.• Increased tubular reabsoption of sodium.
Genitourinary
• Uterus – rises out of pelvis during 1st trimester.
• Weight increases from 70 gms to 1100 gms.• Volume at term averages 5 L but may be as
much as 20 L.
Individual cells increase 100 fold in length by term,
allowing for contractions and involution.
Genitourinary
• Cervix:– Increases in mass and fluid content.– 85% connective tissue and 15% smooth
muscle.– Ripening occurs via softening and effacement
with the influence of hormones.
Gastrointestinal
• Mouth – changes in tastes, increase in saliva production, gums swell and bleed easier.
• Esophagus – decreased tone leads to reflux.
• Stomach – decreased tone and motility.• Intestines – smooth muscle relaxation and
decreased tone and motility - constipation
Gastrointestinal
• Esophagus, stomach and intestines move as uterus grows.
• Round ligament stretches as uterus expands.
• Gallbladder –decrease tone and motilitycombined with increased emptying time can
cause increased risk of gallstones.
Gastrointestinal
• Hyperemesis – common in first trimester.– Strong sense of smell.– Increased saliva production.– Can persist throughout pregnancy.
Immunological
• Placenta functions to help protect the fetus from infection with IgG.
• Decreased Tcell activity with pregnancy that increases susceptibility to viral infections.
• Immunity is enhanced by sleep/rest and decreased stress.
Musculoskeletal
• Abdominal muscles relax and pelvis tilts forward.
• Center of gravity shifts.• Joints relax – waddling.• Muscle aches from increasing weight of
uterus.• Posture change due to lumbodorsal curve
of spine.
Musculoskeletal
• Normal weight gain 25-35#.
• Slight weight loss in 1st trimester from
nausea and vomiting.
Average 1#/wk weight gain in 2nd and 3rd trimesters.
Endocrine
• Thyroid:• Function increases to meet metabolic and growth
needs.
• Parathyroid:• Helps regulate calcium, phosphorus, Vit. D and
magnesium concentration.• Increases in pregnancy to help skeletal growth.