Normal Pregnancy

Question 1

Fertilization

Answer 1

Intercourse must occur prior to ovulation for successful fertilization to occur.

• Egg released from ovary in metaphase II surrounded by cumulus oophorus (granulosa cells) and zona pellucida
• At the same time sperm is moving through cervical mucus and uterus
• Sperm undergoes capitation and acrosome reaction
• Sperm and egg meet in the ampulla of the fallopian tube
• Sperm passes the zona pellucida, attaches to the cell membrane and enters the cytoplasm
• Completion of a second meiotic division ⇒ male and female pronucleus (haploid set of chromosomes)
• Nuclear membrane disappears and diploid set of chromosomes is reestablished
• Once the zygote is formed the cells will continue to divide
  
  • Division allows for the potential for twinning
  • Twinning may occur at any stage until the formation of the blastula
  • Occurs by the separation of the two cells produced by cleavage
  • Each cell has the potential to develop into an embryo

Question 2

Types of Twins

Answer 2

• Diamniotic/dichorionic: prior to 3 days post fertilization
• Diamniotic/monochorionic: 4-8 days post fertilization
• Monoamniotic/monochorionic: 9-12 days post fertilization
• Conjoined: 12 days or more post fertilization

The embryo continues to divide as it travels through the fallopian tube

Enters the uterus in 3-4 days after fertilization

Question 3

Implantation

Answer 3

• Implantation can be as early as 6 days after fertilization
• Usually 3 days after embryo enters the uterus
• zona pellucida must be removed prior to implantation
• Endometrial capillaries come in contact w/ invading syncytiotrophoblasts ⇒ engulfed to form venous sinuses (generally 7.5 days after conception)
• ER of the syncytiotrophoblasts is responsible for production of human chorionic gonadotropin (HCG)
• HCG enters maternal circulation ⇒ corpus luteum maintained
• Corpus luteum maintains pregnancy until the placenta takes over
• Progesterone is steroid of greatest importance in maintaining pregnancy
• After 7 wks, placenta becomes the dominate place for steroid production

Question 4

Embryology

Answer 4

• Embryonic period is the first 49 days after conception
  
  • Organogenesis is complete at this time
• Effects of Teratogens:
  
  • Susceptibility to a teratogen depends on:
  • Genotype of the conceptus
  • Manner in which genotype interacts w/ environmental factors
  • Developmental stage at the time of exposure
• Wks 2-8 is when most structural defects occur
• Teratogens act by different mechanisms
  
  • Alter normal cellular or biochemical processes

Question 5

Maternal Cardiovascular Changes

Answer 5

Earliest and most dramatic changes

Changes are to improve the fetal oxygenation and nutrition

• Anatomic changes:
  
  • Heart displaced upward and to the left
  • Assumes more horizontal position
    
    • Result of diaphragmatic elevation from displacement of abdl viscera by expanding uterus
  • ↑ Ventricular mass
  • ↑ LV and LA size d/t ↑ Circulating blood volume
• Functional changes:
  
  • 1° functional change is ↑ cardiac output (CO)
    
    • Overall CO ↑ 30-50%
      
      • ↑ 50% by 8 wks
    • Relative ↓ blood flow→ splanchnic and skeletal muscle (absolute amount ↔︎)
    • 20% of CO (750cc/min) →uterus at term
    • First half of pregnancy
    • ↑ Stroke volume ⇒ ↑ CO
      
      • ∆ SV d/t ∆ circulating blood volume (peak ↑ at 32 wks) and systemic vascular resistance
      • ↑ Progesterone ⇒ ↓ SVR
        
        • ↓ Smooth muscle tone and AV shunting to uteroplacental circulation
        • ↑ Vasodilatory substances (progesterone, NO, and ANP)
    • Second half of pregnancy
      
      • ↑ HR and SV returns to nl ⇒ ↑ CO
  • Blood pressure
    
    • ↓ Through 2^nd trimester
    • Normalizes toward the end of pregnancy
  • Pulse
    
    • ↑ Resting HR throughout pregnancy
• Physical findings:
  
  • ↑ 2^nd heart sound split
  • Inspiration ⇒ distended neck veins
  • Low grade systolic ejection murmurs
• Symptoms:
  
  • Some women have dizziness and syncope

Question 6

Maternal Respiratory Changes

Answer 6

1° mediated by progesterone

Changes occur d/t ↑ oxygen demand of mother and fetus

• Anatomic changes
  
  • Elevation of diaphragm ~ 4 cm
  • ↑ Chest diameter and circumference
• Functional changes
  
  • ↑ Total body oxygen consumption
    
    • Gravid uterus, Respiratory muscles, Heart and kidneys, Mammary tissue, Elevated diaphragm
  • ↓ Residual volume
  • ↓ Functional residual volume
  • ↓ Total lung volume
  • ↑ Tidal volume
  • ↑ Inspiratory capacity and minute ventilation
    
    • ↑ ventilation and ↓ PCO₂
      
      • Respiratory alkalosis
        
        • Compensated by ↑ excretion of bicarbonate via kidneys
        • Maintains normal maternal arterial pH
• Physical findings: no change
• Symptoms: Dyspnea

Question 7

Maternal Hematologic Changes

Answer 7

• ↑ Plasma volume (50%)
• ↑ Red cell volume
• ↑ Coagulation factors
• ↑ total oxygen carrying capacity
  
  • D/t ↑ oxygen delivery to lungs and [Hb] in blood
• Physiologic anemia
  
  • ↑ Plasma volume > ↑ RBC volume ⇒ normal anemia ass. w/ pregnancy
  • Worse around 30-34 wks
• Lungs
  
  • ↑ Hb affinity for O₂
• Placenta
  
  • ↑ CO₂ gradient b/t fetus and mother ⇒ allows for transfer of CO2 from fetus → mother
• Symptoms: edema

Question 8

Maternal Immune Changes

Answer 8

Physiologic ↑ in WBCs

Question 9

Maternal Coagulation Changes

Answer 9

Hypercoagulable state

↑ Procoagulant factors

↑ Venous stasis

Question 10

Maternal Renal Changes

Answer 10

• Kidneys enlarge
• Dilation of ureters
• ↑ Renal plasma flow
  
  • ↓ BUN and creatinine

Question 11

Maternal GI Changes

Answer 11

• ↓ Tone and motility of stomach
• ↑ GERD
• ↑ Constipation
• ↑ Risk of gallstones

Question 12

Maternal Breast Changes

Answer 12

Initially enlarge d/t vascular engorgement

Further enlarge d/t ↑ mass

Question 13

Maternal Skin Changes

Answer 13

• Hirsutism
• Striae
• Hyperpigmentation
  
  • Linea nigra
  • Melasma

Question 14

Maternal Physiological Changes

Summary

Answer 14

Question 15

Placenta

Functions

Answer 15

• Respiratory exchange
  
  • All gases cross placenta via simple diffusion
  • Dependent on blood carrying capacity of mother and fetus
  • Uterine and umbilical blood flow
• Metabolite exchange
  
  • Glucose is the single primary metabolic substrate for placental metabolism
    
    • Facilitated diffusion
  • Other solutes dependent on concentration gradient, degree of ionization, size and lipid solubility
• Hormone production
  
  • Estrogen
  • Progesterone
  • Human chorionic gonadotropin
  • Human placental lactogen

Question 16

Fetal Circulation

Answer 16

• Oxygenation of fetal blood occurs in the placenta
• Oxygenated blood carried by umbilical vein → portal system
• 50% of blood flows through ductus venosus → foramen ovale → left ventricle
• Blood from proximal aorta → brain and upper body
• Blood from distal aorta → lower body and umbilical arteries
• Blood is deoxygenated and returns to the placenta

Question 17

Prenatal Care

Timeline

Answer 17

Question 18

Diagnosis of Pregnancy

Answer 18

• History
  
  • Amenorrhea
  • Fatigue, N/V, breast tenderness
• Physical
  
  • Enlarged, softened uterus
  • Chadwick’s sign: bluish discoloration of vagina and cervix
  • Hegar’s sign: softening of the cervix
• Laboratory
  
  • UPT: measures HCG
    
    • HCG shares alpha subunit w/ LH, test must differentiate
      
      • Tests for beta subunit of HCG
    • ⊕ by 4 wks, best on early morning urine (highest concentration)
  • Serum pregnancy test: measures HCG
    
    • More sensitive and specific than urine
    • Can get a quantitative result
• Ultrasound
  
  • Transvaginal: able to see at beta HCG of 1000-2000 mIU/mL
  • Transabdominal: able to see at beta HCG of 5000-6000 mIU/mL
  • Cardiac activity detectable at > 4000 MIU/mL (~12 wks)

Question 19

Dating

Answer 19

• Gestational age
  
  • Number of wks since last period
  • Not conceptual age
• Naegle’s rule
  
  • LMP + 7 days – 3 months = Estimated Delivery Date (EDD)
  • 1^st day of LNM is crucial
• Gestation is 40 +/- 2 wks

Question 20

Initial Labs

Answer 20

• Blood type
  
  • Rh status is important
• Antibody screen
• CBC: H&H and Platelets
• Maternal infections or immunity
  
  • Rubella; Hepatitis B surface antigen; Hepatitis C antibody; RPR; HIV; Gonorrhea; Chlamydia; Varicella
• Pap for evaluation of cervical dysplasia/cancer
• Cystic fibrosis and spinal muscular atrophy (SMA) carrier screening
• Hemoglobin electrophoresis to look for Sickle Cell trait and other hemoglobinopathies
• Urinalysis and Urine culture

Question 21

Prenatal Care

Summary

Answer 21

Question 22

Normal Labor

Answer 22

• Progressive change in a woman’s cervix in the setting of regular, rhythmic uterine contractions.
• Spontaneous contractions occur throughout pregnancy, most go unperceived
• Contractions become stronger and more frequent toward term
• Braxton-Hicks: contractions that are perceived but not associated w/ cervical change
  
  • False labor
  • Typically shorter and less intense than true labor

Question 23

Evaluation of Labor

Historical Aspects

Answer 23

• Contractions every 5 minutes for 1 hour
• Leaking of vaginal fluid
• Significant vaginal bleeding
• ↓ Fetal movement

Question 24

Evaluation of Labor

Physical Exam

Answer 24

• Fetal heart tracing
• Tocodynamometer: measurement of contractions
• Cervical exam
  
  • Dilation
  • Effacement
  • Station
  • Fetal lie
  • Presentation
  • Position

Question 25

Cervical

Effacement and Dilation

Answer 25

• Dilation: opening of cervical os
  
  • Measured in cm from 0-10
• Effacement: shortening of cervical canal
  
  • Expressed as a percentage

Question 26

Station

Answer 26

Level of fetal presenting part in the birth canal in relation to ischial spines.

• Measured as a 6- or 10-point scale
• Zero station ⇒ fetal presenting part at the level of the ischial spines
• Positive numbers ⇒ fetal presenting part below the level of the ischial spines
• Negative numbers ⇒ fetal presenting part above the level of the ischial spines

Question 27

Fetal Lie & Presentation

Answer 27

• Fetal Lie: relation of long axis of fetus w/ maternal long axis
  
  • Longitudinal
  • Transverse
  • Oblique
• Presentation: what is the presenting part lowest in the birth canal
  
  • Vertex
  • Breech

Question 28

Position

Answer 28

Relation of presenting part to the right or left side of maternal pelvis.

Question 29

Physiology of Labor

Answer 29