Maternal Changes in Pregnancy

Question 1

Describe ovulation.

Answer 1

• Ovarian follicle (oocyte and surrounding tissue) matures and is ejected.
• Surrounding structure becomes corpus luteum, which quickly starts to make oestrogen and progesterone.

Question 2

What happens on day 1 of pregnancy?

Answer 2

• Fertilisation
• Egg is usually fertilised in 12-24 hours to form a zygote.

Question 3

What has the zygote become by day 4?

Answer 3

Blastocyst

Question 4

Describe what happens on day 5.

Answer 4

• Implantation​
• Corpus luteum makes more progesterone than oestrogen.
• This low oestrogen : progesterone ratio is necessary for implantation.

Question 5

Describe what happens to the blastocyst.

Answer 5

• The inner cells will eventually become the foetus.
• The outer cells become the trophoblast which differentiates to become the placenta. This happens on day 6.

Question 6

What is the action of trophoblastic cells?

Answer 6

• Differentiate to become the placenta. ​
• Cells start to produce HCG ~ day 8.
• This has 2 actions:
  
  • Tells the corpus luteum there has been successful implantation and that it should keep producing oestrogen and progesterone.
  • The continued presence of oestrogen and progesterone suppresses the development of other ovarian follicles.

Question 7

What would happen without the rise of HCG on day 8?

Answer 7

• Corpus luteum would shrivel by day 10 and oestrogen and progesterone levels would fall.
• This would cause endometrial sloughing (menses).

Question 8

What happens to HCG levels in week 9?

Answer 8

• HCG levels peak in week 9, then drop off.
• This is the signal for the corpus luteum to degenetate.
• As this happens, the placenta takes over.

Question 9

What is produced by syncytiotrophoblast cells?

Answer 9

• Progesterone
• Estriol (most abundant oestrogen)
• Placenta also makes some HCG and human placental lactogen (hPL).

Question 10

What is the effect of human placental lactogen (hPL)?

Answer 10

• Counters the effect of maternal insulin to ensure there is plenty of glucose available for the foetus.

Question 11

What happens to blood volume during pregnancy?

Answer 11

• Increases by 30-50%
• 5L of blood becomes 7.5L by the 3rd trimester
• There is a little increase in RBCs and a large increase in plasma, so Hb is reduced.
  
  • This is called the physiological anaemia of pregnancy.

Question 12

What happens to HR during pegnancy?

Answer 12

• Increases by ~20bpm
• This causes mild hypertrophy of the heart which disappears after pregnancy.

Question 13

Describe the changes in heart sounds associated with pregnancy.

Answer 13

• 3rd heart sound (physiological S3)
• Split S1 due to mitral valve closing slightly faster than tricuspid valve)

Question 14

What happens to BP during a normal pregnancy?

What happens to it when lying down in later pregnancy?

Answer 14

• Decreases
• Even although there is an increased volume, BP decreases because progesterone causes vasodilation.
• When lying down in later pregnancy, IVC is compressed resulting in less blood entering the right atrium and therefore hypotension.

Question 15

Describe the changes to the kidneys which occur during pregnancy.

Answer 15

• Increased blood flow, therefore increases in GFR and urine output.
• Kidneys compensate for this by increasing in size:
  
  • dilation of calyces
  • dilation of renal pelvis
• This causes physiologic hydronephrosis, resulting in increased size of ureters (physiologic hydroureter).
• Progesterone causes hypomotility of ureters.
• The increased capacity to store urine and hypomotility of ureters cause urinary stasis in the kidney which increases the risk of upper UTIs.

Question 16

Describe what happens to the respiratory tract during pregnancy.

Answer 16

• Uterus pushes up on the diaphragm, making it harder to breathe comfortably.
• There is some compensation for this because progesterone relaxes the ligaments in the thorax, which increases transverse and anteroposterior diameter of the rib cage.
  
  • This causes increased tidal volume and increased minute volume and therefore decreased CO₂.
• Decreased CO₂ causes mild respiratory alkalosis.
  
  • ​This enhances gas exchange across the placenta making it easier for the foetus to get O₂.

Question 17

What effect does oestrogen have on the upper respiratory tract?

Answer 17

• Increased vascularisation
• Increased capillary engorgement
• These can result in:
  
  • Nasal stuffiness
  • Sinus congestion
  • Nosebleeds

Question 18

Describe the preparation of the skeletal structures in the pelvis for delivery.

Answer 18

• Progesterone and relaxin loosen the ligaments in the sacroiliac joints and pubic symphysis.
• However, this can cause pain in other joints.

Question 19

Describe the GI changes associated with pregnancy.

Answer 19

• In GIT, hormones cause smooth muscle relaxation and decreased peristalsis.
  
  • Can cause constipation and bloating.
• Also causes relaxation of the lower oesophageal sphincter.
  
  • Gastric reflux and heartburn - manage with PPIs (be careful, some CI in pregnancy).
• Morning sickness (any time of day) - nausea and vomiting due to increased HCG.
• Changes in taste - some women develop pica (craving for non-food items).

Question 20

What are the effects of pregnancy on the brain?

Answer 20

• Increases in oestrogen and progesterone can cause:
  
  • Irritability
  • Anxiety
  • Depression
  • Mental foginess
  • Decreased concentration
  • Fatigue and sleep deprivation

Question 21

Describe the hormonal changes which promote lactation.

Answer 21

• Oestrogen and progesterone promote breast development.
• Increased blood flow to the breast.
• Oestrogen stimulates the anterior pituitary to produce prolactin.
• High progesterone during pregnancy inhibits prolactin’s ‘milk letdown’ effect until te baby is born and oestrogen and progesterone levels decrease.

Question 22

What happens to the thyroid gland during pregnancy?

Answer 22

Increased thyroid hormone production causes increased cellular basal rate in order to meet the demands of pregnancy.

Question 23

What happens to the blood during pregnancy in terms of coagulation?

Answer 23

• Oestrogen promotes clotting by increasing plasma fibrinogen and activity of coagulation factors, plus it enhances platelet aggregation.
• Simultaneously, oestrogen decreases the activity of antithrombin III which normal inhibits coagulation.
• Pregnancy is a hypercoagulable state.
• Pro - decreased bleeding at delivery
• Con - increased risk of VTE, especially in lower legs where there is already venous stasis.

Question 24

What is the level of weight gain associated with pregnancy?

Answer 24

• ~25-35lbs
• Due to:
  
  • Increased blood volume
  • Foetus
  • Fat stores
  • Uterus
  • Placenta
• These factors, plus the forward shift in COG can cause lumbar lordosis.