MATERNAL PHYSIOLOGY

Chukwuma I. Onyeije, M.D.Atlanta Perinatal AssociatesClinical Assoc. Professor

Morehouse School of Medicinehttp://maternalfetalmedicineblog.comhttp://onyeije.net/present

Objectives

• Detail normal physiologic changes in the following maternal systems:– Cardiovascular– Respiratory– Renal– Hematologic– Gastrointestinal– Reproductive systems.

• Describe the implications for these changes for normal and abnormal pregnancies.

Objectives

• Review nutritional requirements normal pregnancy

• Review components and reasons for the medical evaluation at the first prenatal visit

• Give the reason for routine laboratory tests obtained early in pregnancy.

BULLET POINTS:

Dilutional anemia of pregnancy:

Lower hematocrit due to expansion of plasma volume

which is greater than the increase in red blood cell

mass

BULLET POINTS:

Pregnancy is a Hypercoagulable state:

Increased risk for venous clotting episodes

BULLET POINTS:

Hegar's sign:

Cervix appears bluish and engorged

BULLET POINTS:MSAFP

(Maternal serum alpha-fetoprotein)

Screening test of maternal blood

done in the early second trimester to screen pregnant women for fetal

anomalies and chromosomal abnormalities

BULLET POINTS:

Bacterial vaginosis:

Bacterial infection of the vagina associated with preterm labor and birth

BULLET POINTS:

Rhogam:

An antibody preparation of anti-Rh factor given to Rh negative women to

prevent Rh isoimmunization

BULLET POINTS:Neural tube defect (NTD):

An abnormality in closure of the neural tube, resulting in

a spectrum of anomalies from anencephaly (no

cranium or cerebrum) to spina bifida

BULLET POINTS:

Intrauterine growth restriction (IUGR): pathological condition of abnormal

placentation resulting in an undergrown fetus

Small-for-gestational age (SGA): the lower 10% of

birthweights

BULLET POINTS:

Large-for-gestational age (LGA): the upper 10% of

birthweights

Macrosomia: an abnormally large infant

(usually > 4000 gm)

The primary goal of prenatal care is to

deliver a healthy term infant without impairing the mothers health and

to identify and optimally treat the high-risk mother.

The vast majority of pregnancies are uncomplicated.

Excessive intervention during pregnancy can

result in less than optimal outcome

THE THE CARDIOVASCULAR CARDIOVASCULAR

SYSTEM:SYSTEM:

THE CARDIOVASCULAR THE CARDIOVASCULAR SYSTEM:SYSTEM:

• Cardiac output increases 30-50% • Stroke volume increases about 10- 15%• Pulse increases about 15-20 bpm• Systolic ejection murmur and S3 gallop

are seen in 90% of pregnant women

CARDIAC OUTPUT DURING PREGNANCY

Peripheral vascular resistance falls

Blood pressure falls during the second trimester and then returns to normal during the third trimester

CLINICAL SIGNIFICANCE:

Many of the NORMAL effects of pregnancy mimic heart failure

(edema, gallops, dyspnea, distended neck veins,

abnormal cardiac silhouette on CXR, EKG

changes).

THE THE RESPIRATORY RESPIRATORY

SYSTEM:SYSTEM:

Lung volumes changes in pregnancy

NO CHANGE:

Respiratory rate, Vital capacity,

Inspiratory reserve volume

DECREASED:

Functional residual capacity Expiratory reserve volume

Residual volume Total lung capacity

INCREASED:

Inspiratory capacity Tidal volume

BLOOD GASES:CLINICAL

SIGNIFICANCE:

The normal pregnant woman has a

compensated respiratory alkalosis and a diminished

pulmonary reserve.

THE THE RENAL RENAL

SYSTEM:SYSTEM:

ANATOMIC RENAL CHANGES:

Kidneys increase in size and weight,

Dilatation of ureters (R > L)

Bladder becomes an intra-abdominal organ

HEMODYNAMIC RENAL CHANGES:

GFR increases 50%,

Renal plasma flow increases by 75%

Creatinine clearance increases to 150-200

cc/min

METABOLIC RENAL CHANGES

BUN and serum creatinine decrease by 25%

Increase in tubular reabsorption of sodium

Increase in glucose excretion

METABOLIC RENAL CHANGES

Plasma osmolarity decreases about 10 mOsm/kg H2O

Marked increase in renin and angiotensin levels, BUT

markedly reduced vascular sensitivity to their

hypertensive effects

CLINICAL SIGNIFICANCE of RENAL CHANGES

:

Pregnant women are at increased risk for prone to

pyelonephritis

Pregnant women are at increased risk for bladder rupture during abdominal

trauma.

THE HEMATOLOGIC

SYSTEM

Plasma volume Plasma volume and RBC massand RBC mass

Plasma volume increases by about 50%

RBC volume increases by about 30%

Plasma volume Plasma volume and RBC massand RBC mass

END RESULT:END RESULT:

”Dilutional anemia of pregnancy",

Average hemoglobin during pregnancy is 11.5 g/dl

Plasma volume Plasma volume and RBC massand RBC mass

OTHER HEMATOLOGIC

CHANGES:

WBC count increases

Platelet count decreases, but stays within normal limits

COAGULATION SYSTEM:

Pregnancy is a "hypercoagulable state"

Increased levels of fibrinogen, factor VII-X

The placenta produces a plasminogen activator inhibitor

CLINICAL SIGNIFICANCE:

Blood loss is well-tolerated during labor.

However: maternal vital signs DO NOT change for blood loss of up to 1500 cc,

Therefore: vital signs cannot be trusted as an indicator of blood loss.

THE GASTROINTESTINAL AND REPRODUCTIVE

SYSTEMS

Gastrointestinal System

Decreased motility, due to influence of progesterone

Reduced gastric acid secretion

Gastrointestinal System

CLINICAL SIGNIFICANCE:

A pregnant woman is considered to have a full stomach even if she has had nothing to eat or drink for several hours.

Peptic ulceration is rare during pregnancy.

Reproductive System

Weight of the Uterus increases from 70 gm to

1100 gm

Blood flow: increases to about 750 cc/min, or 10-

15% of cardiac output

NUTRITIONAL CONSIDERATIONS

DURING PREGNANCY

PREGNANCY WEIGHT GAIN BY PREGNANCY WEIGHT GAIN BY ORGAN SYSTEM: ORGAN SYSTEM:

Fetus: 7 poundsPlacenta and amniotic fluid-- 3 poundsBlood volume-- 4 poundsBreasts-- 2 poundsMaternal fat-- 4 pounds

ANTICIPATED TOTAL: 20 pounds

Average weight gain

THERE IS NO SUCH THING AS “OPTIMAL”

WEIGHT GAIN

Normal BMI: 20 lbsUnderweight BMI: 30 lbsOverweight BMI 16 lbs

Daily dietary requirements

Calories: Increased 15% to ~ 2200 cal/day

Protein: An additional 10 to 30 gm /day ~ 75 gm/day total

Iron supplementation 30 to 60 mg per day

Calcium: 1200 mg needed per day, usually provided by a quart of milk per day or 2 Tums/day,

Folate: supplement 200 to 400 mcg per day

In women with a prior history of having a baby with a neural tube defect, supplementing with 4 mg per day (4000 mcg) has been shown to decrease the risk of a recurrence in the next pregnancy

The pregnant patient is best served by having a

healthy balanced diet with iron and folate supplementation.

Only rarely are other vitamin supplements

necessary

PRENATAL CARE

The first prenatal visit

Decide: Is this patient normal or high-risk?

RISK FOR DOWN SYNDROME (AND OTHER CHROMOSOMAL ABNORMALITIES)

BASED ON MOTHER'S AGE

1/7

1/9

1/50 1/

40

1/30

1/24

1/20

1/15

1/12

1/27

0

1/20

0

1/34

0

1/32

0

1/38

5

1/37

0

1/50

0

1/45

0

1/65

1/80

1/10

0

1/13

0

1/17

0

0.0%

4.0%

8.0%

12.0%

16.0%

15-24

25-29

30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49

#REF!

COMMON COMPLAINTS

OFPREGNANCY

Nausea and vomiting: usually dissipates by 15 weeks

Constipation: common throughout pregnancy

Heartburn: often worsens as pregnancy progresses

Vaginitis: treat only if

symptomatic

Varicose veins: treat symptomatically

Headaches

Lower extremity edema is very common

Backache: Lordosis is common with change in the center of

gravity

Faintness and light-headedness

Carpal tunnel

syndrome

REVIEW QUESTIONS:

Which of the following INCREASES in pregnancy?FRCERVRVTV

During which of the following states is the blood pressure lowest?First trimesterSecond trimesterThird trimesterNon pregnant

All of the following are increased in pregnancy except:Renal plasma flowGFRSerum creatinineTubular sodium resorption

CONCLUSION:

–Understanding maternal physiology is crucial in understanding the changes associated in pregnancy

CONCLUSION:

–This knowledge will help us distinguish the physiologic and pathologic processes during pregnancy

–This knowledge is also necessary to improve patient education about pregnancy

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