Maternal Adaptations for Pregnancy

Question 1

How does menstruation prepare the maternal body for pregnancy?

Answer 1

• The formation of the functional endometrial layer as well as the secretion of progesterone by the corpus luteum prime the body for pregnancy
• Menstruation also allows the uterus to expel all unfertilised eggs and sick, dying or dead embryos to prepare the optimal environment for implantation

Question 2

What organs contribute to the maternal adaptation to pregnancy?

Answer 2

1. Ovaries: prior to 9 weeks of gestation, the corpus luteum in the ovary produces progesterone the growing follicles produce estrogen
2. Placenta:
   - Early in pregnancy the syncytiotrophoblast produces high levels of human chorionic gonadotropin hormone which rescues the corpus luteum and helps maintain progesterone production in the first trimester
   - In the second trimester onwards, the placenta becomes the primary source of hCG, progesterone and estrogen
   - The placenta also produces placental lactogen which increases maternal appetite and fat stores and drives breast development as well as driving maternal insulin resistance

Question 3

What are the fetal needs that must be met during pregnancy?

Answer 3

1. Oxygen
2. Nutrients- fats, glucose, protein, minerals
3. Waste removal
4. Thermoregulation
5. Protection
6. Physical Support
7. Immune Protection

Question 4

What are the categories of maternal adaptations to pregnancy?

Answer 4

1. Hematologic changes
2. Cardiovascular changes
3. Respiratory changes
4. Renal changes
5. Gastrointestinal changes
6. Hepatic changes
7. Metabolic changes

• In summary the maternal organs must function more efficiently to meet the needs to the fetus in terms of nutrient supply and waste removal and the body must also prepare for parturition and lactation

Question 5

Describe the hematologic changes that occur during pregnancy:

Answer 5

1. 40-50% increase in plasma volume
2. 20-30% increase in RBCs

• Both of these are to maintain perfusion of maternal organs and compensate for increased uterine blood flow

3. Increased clotting factors
   - to prevent hemorrhage during delivery

Question 6

Describe the CVS changes that occur during pregnancy:

Answer 6

1. 30-50% increase in cardiac output
   - due to increased stroke volume and HR
   - driven by progesterone, estrogen and fall in vascular resistance (due to placenta)
2. Redistribution of cardiac output:
   - Increase in uterine blood flow (50-750ml/min)
   - Increase in pulmonary blood flow (6-8.5L/min)
   - Increase in renal blood flow (.8-1.2L/min)- due to need to filter fetuses additional waste as well as increased plasma volume
3. Reversible myocardial hypertrophy

Question 7

Describe the respiratory changes that take place during pregnancy:

Answer 7

1. 25-30% increase in oxygen consumption and carbondioxide production
   - due to high metabolic activity of fetus and placenta
2. 30-50% increase in minute ventilation
   - increased progesterone reset breathing centres in the brain so a lower concentration of carbon dioxide in the blood trigger breathing
3. Increased tidal volume
4. Reduction in residual volume
   - compensation for reduced chest cavity size

Question 8

What are the renal changes in pregnancy?

Answer 8

1. Increased renal blood flow
2. Increased GFR- due to greater plasma volume
3. Increased tubular sodium and water reabsorption- to maintain plasma volume
4. Dilated ureters- due to increased progesterone
5. Displacement of bladder

Question 9

Describe the gastrointestinal changes during pregnancy:

Answer 9

1. Decreased motility of intestines and thus increased small intestine time- due to higher progesterone and estrogen levels
2. Increased duodenal villi height and surface area- increased absorptive capacity
3. Increased colonic absorption- helps absorb further water and nutrients

Question 10

Describe the hepatic changes during pregnancy:

Answer 10

1. Increased production of cholesterol and lipids- essential for production of sex hormones
2. Delayed gallbladder contraction- due to progesterone
3. Increased production of clotting factors

Question 11

Describe the metabolic changes that occur during pregnancy:

Answer 11

Placental lactogen is produced by placenta which:

1. Increases appetite, increases fat stores and drives breast development
2. Increases maternal insulin resistance which increases the amount of insulin and thus glucose, amino acids and lipids in maternal circulation

Increased production of maternal thyrotropin:

• Increased metabolic rate
• Increased appetite