Table 1-1. Estrogens Throughout a Woman’s Life



Estradiol Nonpregnant Follicle
  reproductive years Granulosa
     
Estriol Pregnancy Placenta
    from fetal adrenal DHEAS
     
Estrone After menopause Adipose
    from adrenal steroids
     

 

 

PHYSIOLOGIC CHANGES IN PREGNANCY

 

Skin

 

Striae gravidarum—“Stretch marks” that develop in genetically predisposed women on theabdomen and buttocks.

 

Spider angiomata and palmer erythema—From increased skin vascularity.

 

Chadwick sign—Bluish or purplish discoloration of the vagina and cervix as a result ofincreased vascularity.

 

Linea nigra—Increased pigmentation of the lower abdominal midline from the pubis to theumbilicus.

 

Chloasma—Blotchy pigmentation of the nose and face.


 

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Cardiovascular

Arterial blood pressure—Systolic and diastolic values both decline early in the first trimester,reaching a nadir by 24–28 weeks, then they gradually rise toward term but never return quite to prepregnancy baseline. Diastolic falls more than systolic, as much as 15 mm Hg. Arterial blood pressure is never normally elevated in pregnancy.

 

Venous blood pressure—Central venous pressure (CVP) is unchanged with pregnancy, butfemoral venous pressure (FVP) increases two- to threefold by 30 weeks’ gestation.

 

Plasma volume—Plasma volume increases up to 50% with a significant increase by the firsttrimester. Maximum increase is by 30 weeks. This increase is even greater with multiple fetuses.

 

Systemic vascular resistance (SVR)—SVR equals blood pressure (BP) divided by cardiac out-put (CO). Because BP decreases and CO increases, SVR declines by 30%, reaching its nadir by 20 weeks. This enhances uteroplacental perfusion.

 

Cardiac output (CO)—CO increases up to 50% with the major increase by 20 weeks. CO isthe product of heart rate (HR) and stroke volume (SV), and both increase in pregnancy. HR increases by 20 beats/min by the third trimester. SV increases by 30% by the end of the first tri-mester. CO is dependent on maternal position. CO is the lowest in the supine position because of inferior vena cava compression resulting in decreased cardiac return. CO is the highest in the left lateral position. CO increases progressively through the three stages of labor.

 

Murmurs—A systolic ejection murmur along the left sternal border is normal in pregnancyowing to increased CO passing through the aortic and pulmonary valves. Diastolic murmurs are never normal in pregnancy and must be investigated.

Table 1-2. Cardiovascular Changes

Arterial blood pressure Systolic
     
  Diastolic ↓↓
     
Venous pressure Central Unchanged
     
  Femoral
     
Peripheral vascular resistance  
     

 

 

Hematologic

 

Red blood cells (RBC)—RBC mass increases by 30% in pregnancy; thus, oxygen-carryingcapacity increases. However, because plasma volume increases by 50%, the calculated hemo-globin and hematocrit values decrease by 15%. The nadir of the hemoglobin value is at 28–30 weeks’ gestation. This is a physiologic dilutional effect, not a manifestation of anemia.

 

White blood cells (WBC)—WBC count increases progressively during pregnancy with a meanvalue of up to 16,000/mm3 in the third trimester.

 

Erythrocyte sedimentation rate (ESR)—ESR increases in pregnancy because of the increasein gamma globulins.

 

Platelet count—Platelet count normal reference range is unchanged in pregnancy.

 

Coagulation factors—Factors V, VII, VIII, IX, XII, and von Willebrand Factor increase pro-gressively in pregnancy, leading to a hypercoagulable state.

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Gastrointestinal

Stomach—Gastric motility decreases and emptying time increases from the progesteroneeffect on smooth muscle. This increase in stomach residual volume, along with upward dis-placement of intraabdominal contents by the gravid uterus, predisposes to aspiration pneumo-nia with general anesthesia at delivery.

 

Large bowel—Colonic motility decreases and transit time increases from the progesterone effecton smooth muscle. This predisposes to increased colonic fluid absorption resulting in constipation.

 

 

Pulmonary

 

Tidal volume (Vt)—Vt is volume of air that moves in and out of the lungs at rest. Vt increases with pregnancy to 40%. It is the only lung volume that does not decrease with pregnancy.

 

• •                                                                             

 

Minute ventilation (Ve)—Ve increases up to 40% with the major increase by 20 weeks. Ve isthe product of respiratory rate (RR) and Vt. RR remains unchanged with Vt increasing steadily throughout the pregnancy into the third trimester.

 

Residual volume (RV)—RV is the volume of air trapped in the lungs after deepest expiration.RV decreases up to 20% by the third trimester. To a great extent this is because of the upward displacement of intraabdominal contents against the diaphragm by the gravid uterus.

 

Blood gases—The rise in Vt produces a respiratory alkalosis with a decrease in Pco2from 40to 35 mm Hg and an increase in pH from 7.40 to 7.45. An increased renal loss of bicarbonate helps compensate, resulting in an alkalotic urine.

 

Nonpregnant

Pregnant

 

Deepest

       

Inspiratory

     
             
       

reserve

     
breath in        

volume

     
possible                  

Breathing

       

Tidal volume

     
             
at rest                  

Deepest breath

                 
                 

out possible

       

Expiratory

       
               

Air you can’t

       

reserve volume

 

 

 

 
         
                 

exhale out

 

 

 

 

Residual volume

 

 

 

 
   

Figure I-1-1. Changes in Pulmonary System

 

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Renal

Kidneys—The kidneys increase in size because of the increase in renal blood flow. This hyper-trophy doesn’t reverse until 3 months postpartum.

 

Ureters—Ureteral diameter increases owing to the progesterone effect on smooth muscle. Theright side dilates more than the left in 90% of patients.

 

Glomerular filtration rate (GFR)—GFR, renal plasma flow, and creatinine clearance all increase by 50% as early as the end of the first trimester. This results in a 25% decrease in serumblood urea nitrogen (BUN), creatinine, and uric acid.

 

Glucosuria—Urine glucose normally increases. Glucose is freely filtered and actively reab-sorbed. However, the tubal reabsorption threshold falls from 195 to 155 mg/dL.

 

Proteinuria—Urine protein remains unchanged.

 

 

Endocrine

 

Pituitary—Pituitary size increases by 100% by term from increasing vascularity. This makes itsusceptible to ischemic injury (Sheehan syndrome) from postpartum hypotension.

 

Adrenals—Adrenal gland size is unchanged, but production of cortisol increases two- tothreefold.

 

Thyroid—Thyroid size increases 15% from increased vascularity. Thyroid binding globulin(TBG) increases, resulting in increased total T3 and T4, although free T3 and free T4 remain unchanged.

 

Fetal Circulation

 

Three in utero shunts exist within the fetus. The ductus venosus carries blood from the umbilical vein to the inferior vena cava. The foramen ovale carries blood from the right to the left atrium, and the ductus arteriosus shunts blood from the pulmonary artery to the descending aorta.

 

Ductus venosus Umbilical vein → inferior vena cava
   
Foramen ovale Right atrium → left atrium
   
Ductus arteriosus Pulmonary artery → descending aorta
   

 

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OB Triad

Fetal Circulation Shunts

 

• Ductus venosus (UA → IVC)

 

• Foramen ovale (RA → LA)

 

• Ductus arteriosus (PA → DA)

 

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PHYSIOLOGY OF LACTATION

 

 

  Subcutaneous fat  
Chest wall Suspensory ligaments  

Pectoralis

Gland lobules  
   
muscles Lactiferous duct  
  Lactiferous sinus  

 

 

Figure I-1-2. Sagittal View of Breast

 

Embryology

 

Breasts begin developing in the embryo about 7 to 8 weeks after conception, consisting only of a thickening or ridge of tissue.

 

• From weeks 12 to 16, tiny groupings of cells begin to branch out, laying the foundation for future ducts and milk-producing glands. Other tissues develop into muscle cells that will form the nipple (the protruding point of the breast) and areola (the darkened tissue surrounding the nipple).

 

• In the later stages of pregnancy, maternal hormones cause breast cells to organize into branching, tubelike structures, thus forming the milk ducts. In the final 8 weeks, lobules (milk-producing glands) mature and actually begin to secrete a liquid substance called colostrum.

 

• In both female and male newborns, swellings underneath the nipples and areolae can easily be felt and a clear liquid discharge (colostrum) can be seen.

 

 

Puberty

 

From infancy to just before puberty, there is no difference between female and male breasts.

 

• With the beginning of female puberty, however, the release of estrogen—at first alone, and then in combination with progesterone when the ovaries functionally mature— causes the breasts to undergo dramatic changes which culminate in the fully mature form.

 

• This process, on average, takes 3 to 4 years and is usually complete by age 16.

 

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Anatomy

The breast is made of lobes of glandular tissue with associated ducts for transfer of milk to the exterior and supportive fibrous and fatty tissue. On average, there are 15 to 20 lobes in each breast, arranged roughly in a wheel-spoke pattern emanating from the nipple area. The distri-bution of the lobes, however, is not even.

 

• There is a preponderance of glandular tissue in the upper outer portion of the breast.

 

This is responsible for the tenderness in this region that many women experience prior to their menstrual cycle.

 

• About 80–85% of normal breast tissue is fat during the reproductive years. The 15 to 20 lobes are further divided into lobules containing alveoli (small saclike features) of secre-tory cells with smaller ducts that conduct milk to larger ducts and finally to a reservoir that lies just under the nipple. In the nonpregnant, nonlactating breast, the alveoli are small.

 

• During pregnancy, the alveoli enlarge; and during lactation, the cells secrete milk substances (proteins and lipids). With the release of oxytocin, the muscular cells sur-rounding the alveoli contract to express the milk during lactation.

 

• Ligaments called Cooper’s ligaments, which keep the breasts in their characteristic shape and position, support breast tissue. In the elderly or during pregnancy, these ligaments become loose or stretched, respectively, and the breasts sag.

 

• The lymphatic system drains excess fluid from the tissues of the breast into the axillary nodes. Lymph nodes along the pathway of drainage screen for foreign bodies such as bacteria or viruses.

 

Hormones

 

Reproductive hormones are important in the development of the breast in puberty and in lactation.

 

Estrogen, released from the ovarian follicle, promotes the growth ducts.

 

Progesterone, released from the corpus luteum, stimulates the development of milk-producing alveolar cells.

 

Prolactin, released from the anterior pituitary gland, stimulates milk production.

 

Oxytocin, released from the posterior pituitary in response to suckling, causes milkejection from the lactating breast.

 

 


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