Maternal adaptations to pregnancy

Question 1

LO

Answer 1

• To explain the concept of ‘foetal autonomy’: how endocrine signals of placental origin alter maternal physiology
• To explain the alterations in the maternal cardiovascular, respiratory, and metabolic systems which optimise the delivery of oxygen and glucose to the foetus
• To examine how the mother’s response to the challenges of pregnancy may be influenced by the environment, with implications for later health of the offspring and the mother

Question 2

What is required to grow a baby?

Answer 2

Question 3

Why must maternal physiology change?

Answer 3

In order to provide for her baby and to provide for herself

Question 4

How must her physiology change to provide for her baby?

Answer 4

There must be an increase in metabolism for oxygen and an increase in nutrients for glucose

Question 5

How must the mothers physiology change to provide for herself?

Answer 5

prepare for metabolic demands of later in pregnancy (fat and protein deposition) - first trimester

prepare for delivery (reproductive tract) and feeding the baby (mammary glands) - later in pregnancy

Question 6

Tell me the hormones that are involved in the foetal anatomy when they signal to the mother

Answer 6

Question 7

How do the levels of the following hormones change over the course of gestation:

hCG

hPL

Progesterone

Estriol

Estrone

Estradiol

Answer 7

Question 8

What are some physiology changes during pregnancy and why do each of those changes occur?

Answer 8

Cardiovascular changes

to supply extra blood to maternal tissues and to the uterine circulation

Renal changes

to achieve expansion of the blood volume and to remove metabolic waste products from the foetus

Respiratory changes

to supply extra oxygen for the increased metabolic demands of both mother and foetus

Metabolic changes

to provide for the mother’s needs and to supply nutrients for the growing foetus

Question 9

Tell me the maternal cardiovascular adaptation and what this helps with

Answer 9

Increase in uterine artery blood flow aids nutrient delivery → ­increase foetal growth

How is this achieved? All about oestrogen

Uterine blood flow increases over the course of pregnancy: this aids foetal growth

This is supported by the graph on the right which shows foetal growth over the course of pregnancy

Question 10

Oestrogen causes blood vessels to do what?

How does it do this?

Answer 10

Vasodilation

Increases the production of locally acting vasodilators e.g., nitric oxide (NO) and prostacyclin

Question 11

What does vasodilation reduce?

Answer 11

Peripheral resistance

Peripheral vascular resistance (systemic vascular resistance, SVR) is the resistance in the circulatory system that is used to create blood pressure, the flow of blood and is also a component of cardiac function. When blood vessels constrict (vasoconstriction) this leads to an increase in SVR.

Question 12

How is cardiac output affected during pregnancy?

What formula is used to show this?

Answer 12

Maternal cardiac output is increased

This adaptation is complete by mid-pregnancy

Cardiac output= blood being pumped out of heart at any one given time

CO= HR (heart rate) X SV (stroke volume- volume of blood being pumped during each heartbeat)

Question 13

Tell me about how maternal systolic and diastolic BP is affected by pregnancy

Answer 13

decreases for most of pregnancy

• decrease in peripheral resistance
• expansion of placental circulation

slight increase to pre-pregnant levels 36 - 40 weeks

BP is monitored during pregnancy - for signs of pre-eclampsia

Decreases systolic and diastolic BP over course of pregnancy- slightly increases at end of pregnancy but never to normal levels

Preeclampsia is when BP gets very high and if left untreated it can lead to seizures and can be fatal

Question 14

How is plasma volume and total body water volume affected during pregnancy?

Answer 14

They are both increased during pregnancy

Increases in blood volume during pregnancy and follows the same pattern as foetal weight gain

Risk of too much fluid in interstitial fluid- due to massive increase of water volume during pregnancy- risk of oedema

Question 15

How is renal function affected during pregnancy?

Answer 15

The achieve maternal plasma volume expansion

1. Change in kidney function

2. Increased activity of the renin-angiotensin-aldosterone system (RAS)

• Regulate retention of sodium and water in kidney

3. Changes in blood osmolality (solute concentration)

• Fluid retention and regulation of thirst

Question 16

How is the maternal kidney function affected during pregnancy?

Answer 16

Increased cardiac output increases renal blood flow

Glomerular filtration rate (GFR) increased by 40%-50%

Sodium and water excretion from the kidney function is regulated by the RAS (renal angiotensin system?)

Question 17

How is the RAS influenced by pregnancy hormones?

Answer 17

Aldosterone from adrenal gland and this regulates sodium and water balance in the kidney

The hormones we see during pregnancy stimulate this whole pathway

Learn the pathway and how a high levels of oestrogen effects the hormonal output of the adrenal gland

All this increases blood volume and fluid retention during pregnancy

Progesterone has an opposite effect but all about balance between the two hormones

Angiotensin II is a vasoconstrictor

Question 18

How is maternal haemodilution affected during pregnancy?

Answer 18

Maternal haemodilution

• Plasma volume increases more than red cell mass

Decreased haemoglobin concentration

• Risk on anaemia- not having enough iron or RBC during pregnancy

Question 19

Tell me that changes that occur in osmoreceptor function

Answer 19

plasma solute concentration (osmolality) is about 10 mOsm/kg less than non-pregnant (more ‘dilute’ blood plasma)

normally, this would decrease anti-diuretic hormone (ADH) secretion to allow more fluid loss

however hypothalamic osmoreceptors have reduced threshold in pregnancy

Question 20

What are the respiratory changes that occur in the mother during pregnancy?

Answer 20

supply of oxygen to maternal tissues must increase

oxygen transfer across the placenta to the foetus must be increased

Question 21

How is the increased oxygen demand met?

Answer 21

No change in respiratory rate, vital capacity, or inspiratory reserve volume, but:

1. tidal volume ­ increased by up to 40%: (tidal volume= breathing in and out)

deeper breathing, ­ increased air flow resulting in increased O2 alveoli absorption

leads to decreased maternal [CO2]- changes metabolics of the mother

2. maternal pulmonary blood flow increase­ by 40% (due to increased­ CO)

per time, more blood available to absorb O2 across lungs

progesterone:

increases sensitivity to decreased [CO2]

causes dilation of airways to get more air into the lungs during pregnancy

­ 3. increased red blood cells → ­increased O2 carrying capacity of the blood

­ 4. Increased 2,3-diphosphoglycerate - an anion which displaces O2 from haemoglobin → more O2 release to tissues

5. foetal Hb has greater affinity for O2 than maternal Hb → enhanced placental O2 transfer

Question 22

How is the maternal metabolism affected during pregnancy?

Answer 22

increase in maternal protein reserved, mothers own metabolism for growth of tissues that will be in use i.e., uterus, muscles and breast tissues towards end of breast feeding at end of birth

–> growth of uterus, musculature, and breast tissue

Early increased in maternal fat reserves- particularly in the first part of pregnancy

Energy store during first part of pregnancy and energy release during the latter part of pregnancy

Fatty acids important- maternal tissues become more insulin resistant in late pregnancy

Question 23

Tell me about maternal insulin resistance during pregnancy

Answer 23

relative insulin resistance results in increase in circulating glucose levels in late pregnancy

• glucose promotes foetal growth

placenta produces anti-insulin factors

• hPL, placental growth hormone, oestrogen, and progesterone

gestational diabetes

Question 24

What if adaptations are not optimal?

Answer 24

What might influence these adaptations?

Problems for mother and/or baby?

Metabolic:

maternal glucose supply

Cardiovascular (CV):

uterine artery blood flow

Placenta

Question 25

Why is pregnancy considered a cardiovascular stress test?

Answer 25

**Pregnancy is a cardiovascular stress test** impaired maternal ability to adjust CV system may increase­ risk of placental dysfunction, poor perfusion - intrauterine growth restriction (IUGR)

Question 26

Impaired cardiovascular adaptations during pregnancy can increase the risk of what?

Answer 26

Later cardiovascular diseases of the mother

Question 27

study of Swedish women categorized by presence of small for gestational age (SGA) and preterm birth in their first delivery (n = 923 686).

Answer 27

Question 28

uterine artery blood flow and foetal growth

Answer 28

Question 29

In a study done on rats about maternal nutrient restriction, they were fed 50% of total nutrient requirement during pregnancy, what outcomes were seen?

Answer 29

33% lower total cardiac output reduced proportion going to uterus 30% reduction in placental blood flow

Question 30

In a study done on rats about maternal protein restriction, they were fed 50% of the protein requirements from day 1, what outcomes were seen?

Answer 30

rats fed 50% of protein requirements from day 1 gestation - decreased sensitivity to vasodilation also associated with reduced plasma volume during gestation maternal nutrient restriction reduces placental perfusion

Question 31

Tell me the effects on maternal nutrient restriction if oestrogen is involved

Answer 31

rats fed 50% requirements last 7 days gestation have reduced oestrogen which had effects on cardiovascular system (Gonzalez et al. (1997) J. Endocrinol. Invest. 20: 397-403) blockade of oestrogen receptor during pregnancy abolishes normally enhanced vasodilation (Bird et al. (2003) Am. J. Physiol. 282: R245-58)

Question 32

What percentage of women have diabetes during pregnancy?

Answer 32

2% 50% are already diabetic 50% become diabetic during pregnancy **(gestational diabetes**) these women are unable to respond to the metabolic 'stress' of pregnancy

Question 33

What does maternal hyperglycaemia result in?

Answer 33

Foetal hyperglycaemia

Question 34

if a mother has hyperglycaemia, what effects can this have?

Answer 34

Increased foetal insulin secretion which promotes excess foetal growth This presents a risk for both mother and baby This may be due to **insulin deficiency, hyperinsulinemia, insulin resistance, obesity?**

Question 35

The increasing prevalence amongst pregnancy women can have what effects?

Answer 35

**increased fat reserves** prior to pregnancy **insulin resistant** compared to normal weight pregnant mothers **gestational diabetes** more common **larger babies but sometimes smaller** i.e., congenital defects **hyperglycaemia** (can cause issues in the foetus)

Question 36

How does maternal obesity affect vascular function?

Answer 36

increased maternal body mass index associated with reduced endothelium-dependent vasodilation implications for foetal nutrient delivery? risk of pre-eclampsia and later hypertension for mother

Question 37

Take home messages

Answer 37

* Oxygen and nutrient supply to the foetus are increased through specific maternal adaptations initiated through endocrine signals originating from the placenta * Maternal cardiac output & blood volume are increased * Blood flow from the mother to the placenta is increased * Maternal inspiratory capacity is increased * Fat reserves in the mother are increased * Maternal blood glucose concentrations are increased * Disturbances in these adaptations may lead to altered fetal growth and to an increased risk of disease in later life for the baby, as well as increased health risks for the mother in her later life