Physiological changes during

pregnancy

M. Kamil

Clinical Case• You are providing prenatal care for a young couple’s first pregnancy that

has proceeded without complication through 38 weeks of gestational age. They come to your office for urgent consultation, fearful for the mother’s life because of her newly diagnosed heart disease. They request prompt referral to a good cardiologist. Upon taking a careful history, you learn they had traveled to a nearby mountain resort for the weekend, 2,000 feet higher above sea level than here at home. Upon arriving, she had experienced new and very disturbing dyspnea and had been seen in an Urgent Care Clinic where a normal electrocardiogram was obtained, but a chest x-ray was reported as grossly abnormal, with her heart “seriously enlarged and deviated from its normal position” consistent with new, severe heart disease.Beckmann, C., Herbert, W., Laube, D., Ling, F., Smith, R., & American College of Obstetricians Gynecologists. (2014). Obstetrics and gynecology (7th ed.).

Physiology changes in pregnancy– Cardiovascular– Respiratory– Hematology– Renal – Gastrointestinal– Skin

CARDIOVASCULAR SYSTEM

Cardiovascular system: Introduction• The earliest and most dramatic changes.

– Improves fetal oxygenation and nutrition.

Cardiovascular system: Anatomic changes• Heart is displaced upward and to the left• Apex is moved laterally• Increase ventricular muscle mass and sizes increase

Pregnancy-associated changes in the cardiac position on a chest x-ray may be confused with cardiac pathology until the pregnancy is recognized.

Cardiovascular system: Functional changes• Marked increase in cardiac output (CO).

– Overall – Increases from 30% to 50%– Half of the increment occur by 8 weeks of gestation– Maximum reached between 20 and 24 weeks’ gestation –> maintained until delivery– Cause by

• Stroke volume• Heart rate (10-18 bpm over the non-pregnant at term)

• Distribution of cardiac output• First trimester - uterus receives about 2% of the cardiac output in the first • At term – increasing to up to 20% at term

About one-fifth of the cardiac output goes through the uterus at term increasing the risk from postpartum hemorrhage substantially.

Cardiovascular system: Functional changes• Systemic vascular resistance decreases during pregnancy - > decrease arterial blood pressure

– Cause by • Elevated progesterone.• Increase production of vasodilatory substance -> PG, NO, ANP

Article · April 2014 · Journal of the American Heart Association

Cardiovascular system: Functional changes• Blood pressure decrease ->Lowest at 24 weeks• SBP of 5 - 10 mm Hg• DBP of 10 - 15 mm Hg • Gradually returns to non-pregnant values by term.

Cardiovascular system: Symptoms

Dizzinesslight-headedness

syncope

Termed the inferior vena cava syndrome

Ineffective shunting via the paravertebral

circulation whenthe gravid uterus

occludes the inferior vena cava

Cardiovascular system: Physical Findings• Increased second heart sound split with inspiration• Distended neck veins • Low-grade systolic ejection murmurs, • S3 gallop, or 3rd heart sound, after 20 weeks

Cardiovascular system: Diagnostic Tests• Serial BP assessment

– Should not be higher than normal person• CXR – cardiac silhouette can appear enlarged (if performed)• ECGs – a slight left-axis deviation

RESPIRATORY SYSTEM

Respiratory System: Introduction• Pregnancy is associated with an increase in total body oxygen consumption of

approximately 50 mL O2/minute, which is 20% greater than nonpregnant levels. • Increased oxygen demand of the mother and fetus.

– These changes are primarily mediated by progesterone.

Respiratory System: Anatomical changes• Diaphragm is elevated approximately 4 cm by late pregnancy• due to the enlarging uterus.• Subcostal angle widens as the chest diameter and

circumference increase slightly

Respiratory System: Functional Changes

• Total body oxygen consumption is 20% greater than non-pregnant levels.– ~50% of this increase is consumed by the gravid uterus and its

contents– 30% by the heart and kidneys– 18% by the respiratory muscles – Remainder by the mammary tissues

Respiratory System: Functional Changes

Diaphragmatic elevation.• 20% reduction in the RV and FRC• 5% reduction in total lung volume• there is a 30% to 40% increase in tidal volume due

to a 5% increase in inspiratory capacity, -> 30% to 40% increase in minute ventilation

Respiratory System: Symptoms

• Dyspnea – A relative hyperventilation occurs in the first

trimester of pregnancy– Pregnant women with normal respiratory rates

often complain of dyspnea.

Respiratory System: Diagnostic Tests

• ABG – Normally shows compensated respiratory alkalosis.

• CXR - Prominent pulmonary vasculature due to the increased circulating blood volume (if performed)

HEMATOLOGIC SYSTEM

Hematologic System: Introduction• To maximize the oxygen-carrying capacity of the mother

– To enhance oxygen delivery to the fetus– Promoting CO2 exchange from fetus to mother

• To minimize the effects of impaired venous return and blood loss associated with labor and delivery.

Hematologic System: Anatomic Changes• Increase maternal plasma volume

– Increase around the sixth week of pregnancy.– Maximum at 30 to 34 weeks of gestation -> stabilizes.

• Increase Red cell volume (by 20-30%)– Leads to a decrease in the hematocrit, or dilutional

anemia. – Important for mother to have adequate iron intake.

The mean increase in plasma volume is approximately 50% in singleton gestations and greater in multiplegestations.

Hematologic System: Anemia management

– Iron from dietary sources usually not sufficient.– Requirement: A total of 1,000 mg of additional iron

• 500 mg is used to increase maternal red cell mass• 300 mg is transported to the fetus• 200 mg is used to compensate for normal iron loss

– National Academy of Sciences recommends:• An iron supplement of 27 mg (present in most prenatal vitamins). • In the form of ferrous sulfate, 60 mg of iron is a dosage of 300 mg. • Patients who are anemic should receive 60 to 120 mg of iron.

Hematologic System: Anatomic Changes• WBC counts

– Typically increase slightly and return to non-pregnant levels during the puerperium. – During labor, the white blood cell count may further increase (Granulocytes)

• Platelet counts - May decline slightly• Other coagulations:

– Increase by 50%• Fibrinogen (factor I) increases by 50%,• Fibrin split products• Factors VII, VIII, IX, and X.

– Remain unchanged• Prothrombin (factor II) • Factors V and XII

– Decreases• activated protein C and protein S

Hematologic System: Functional Changes• Increase O2 delivery to the lungs and Hb in the blood -> Increase in total oxygen carrying capacity.• The compensated respiratory alkalosis of pregnancy

– Causes a shift in the maternal oxygen dissociation curve to the left (Bohr effect). – Result:

• Maternal lungs, Hb affinity for oxygen increases -> Gets more oxygen into the blood• Placenta, the CO2 gradient between fetus and mother is increased -> enhance transfer of CO2

from fetus to mother• The risk of thromboembolism doubles during pregnancy (hypercoagulable state)

– Increases to 5.5 times the normal risk during the puerperium

Hematologic System: Symptoms and physical Findings• Edema

– swelling of the hands, face, legs, ankles, and feet may occur. – Tends to be worse late in pregnancy.

Hematologic System: Diagnostic tests• Physiologic anemia.

– Disproportionate increase in plasma volume, compared with red cell volume, results in a decrease in Hb concentration and hematocrit.

– Average Hb is 12.5 g/dL, (nl 14 g/dL )• Values less than 11.0 g/dL are usually due to iron deficiency.

• Need investigation and should be treated• WBC counts can range from 5,000 to 12,000/L

– Increase to as much as 30,000/L during labor and the puerperium• Coagulation system

– Most notable - Increased concentration of fibrinogen ranges from 300 to 600 mg/dL (nl 200 to 400)

Follow-up• Your patient is 20 years old and has a completely negative medical history. On

physical examination, her blood pressure and pulse rate are normal as is auscultation of her heart and lungs. After this examination, you explain that shortness of breath (dyspnea) is normal in pregnancy because of a lowered CO2 level. In her case, it is probable that she had not noted this until her abrupt introduction into a high-altitude environment. You also show her a picture of a chest x-ray during pregnancy, explaining that her heart is quite normal, simply displaced upward, and somewhat sideways by her growing baby. Reassured, they continue prenatal care and subsequently she has a normal vaginal delivery of a healthy daughter 2 weeks after this visit.Beckmann, C., Herbert, W., Laube, D., Ling, F., Smith, R., & American College of Obstetricians Gynecologists. (2014). Obstetrics and gynecology (7th ed.).

Refrences• Gronowski AM. Handbook of Clinical Laboratory Testing During Pregnancy. Totowa, NJ: Humana

Press; 2004.• World Health Organization. Iron Deficiency Anaemia. Assessment, Prevention, and Control. A guide

for programme managers. 2001. http://www.who.int/nutrition/publications/en/ida_assessment_prevention_control.pdf (Accessed on September 06, 2011).

• Beckmann, C., Herbert, W., Laube, D., Ling, F., Smith, R., & American College of Obstetricians Gynecologists. (2014). Obstetrics and gynecology (7th ed.).

• Callahan, T., & Caughey, A. (2007). Blueprints obstetrics & gynecology (4th ed. / Tamara L. Callahan, Aaron B. Caughey. ed., Blueprints). Philadelphia ; London: Lippincott Williams & Wilkins.

• Lim VS, Katz AI, Lindheimer MD. Acid-base regulation in pregnancy. Am J Physiol 1976; 231:1764.• http://www.uptodate.com/contents/maternal-cardiovascular-and-hemodynamic-adaptations-to-

pregnancy?source=search_result&search=pregnancy+cardiovascular&selectedTitle=1~150