Physiology of pregnancy

Question 1

What three hormones released from the anterior pituitary gland are increased in pregnancy?

Answer 1

ACTH, prolactin and melanocyte stimulating hormone (MSH)

Question 2

What is the consequence of increased ACTH in pregnancy?

Answer 2

Higher ACTH levels cause a rise in steroid hormones, particularly cortisol and aldosterone. Higher steroid levels lead to an improvement in most autoimmune conditions and a susceptibility to diabetes and infections.

Question 3

What is the consequence of increased prolactin in pregnancy?

Answer 3

Increased prolactin acts to suppress FSH and LH, causing reduced FSH and LH levels.

Question 4

What is the consequence of increased MSH in pregnancy

Answer 4

Increased melanocyte stimulating hormone causes increased pigmentation of the skin during pregnancy, resulting in skin changes such as Linea nigra and melasma.

Question 5

What happens to TSH levels in pregnancy?

Answer 5

TSH remains normal, but T3 and T4 levels rise.

Question 6

What happens to HCG levels in pregnancy

Answer 6

HCG levels rise, roughly doubling every 48 hours until they plateau around 8 – 12 weeks, then gradually start to fall.

Question 7

What is the role of progesterone in pregnancy?

Answer 7

Progesterone levels rise throughout pregnancy. Progesterone acts to maintain the pregnancy, prevent contractions and suppress the mother’s immune reaction to foetal antigens. The corpus luteum produces progesterone until ten weeks gestation. The placenta produces it during the remainder of the pregnancy.

Question 8

What changes happen in the uterus & cervix during pregnancy?

Answer 8

The size of the uterus increases from around 100g to 1.1kg during pregnancy. There is hypertrophy of the myometrium and the blood vessels in the uterus. Increased oestrogen may cause cervical ectropion and increased cervical discharge.

Question 9

What happens to the vagina during pregnancy?

Answer 9

Oestrogen also causes hypertrophy of the vaginal muscles and increased vaginal discharge. The changes in the vagina prepare it for delivery, however they make bacterial and candida infection (thrush) more common.

Question 10

Describe some of the cardiovascular changes that occur during pregnancy

Answer 10

1) Increased blood volume
2) Increased plasma volume
3) Increased cardiac output, with increased stroke volume and heart rate
4) Decreased peripheral vascular resistance
5) Decreased blood pressure in early and middle pregnancy, returning to normal by term
6) Varicose veins can occur due to peripheral vasodilation and obstruction of the inferior vena cava by the uterus
7) Peripheral vasodilation also causes flushing and hot sweats

Question 11

Describe some of the respiratory changes that occur during pregnancy

Answer 11

Tidal volume and respiratory rate increase in later pregnancy, to meet the increased oxygen demands.

Question 12

Describe some of the renal changes that occur during pregnancy

Answer 12

1) Increased blood flow to the kidneys
2) Increased glomerular filtration rate (GFR)
3) Increased aldosterone leads to increased salt and water reabsorption and retention
4) Increased protein excretion from the kidneys (normal is up to 0.3g in 24 hours)
5) Dilatation of the ureters and collecting system, leading to a physiological hydronephrosis (more right-sided)

Question 13

Describe the hematological changes in pregnancy

Answer 13

There is increased red blood cell production in pregnancy, leading to higher iron, folate and B12 requirements. Plasma volume increases more than red blood cell volume, leading to a lower concentration of red blood cells. High plasma volume means the haemoglobin concentration and red cell concentration (haematocrit) fall in pregnancy, resulting in anaemia.

Question 14

What happens to clotting factors in pregnancy and what is the risk of this?

Answer 14

Clotting factors such as fibrinogen and factor VII, VIII and X increase in pregnancy, making women hyper-coagulable. This increases the risk of venous thromboembolism (blood clots developing in the veins). Pregnant women are more likely to develop deep vein thrombosis and pulmonary embolism.

Question 15

Describe some other hematological changes that occur in pregnancy

Answer 15

1) Increased white blood cells
2) Decreased platelet count
3) Increased ESR and D-dimer
4) Increased alkaline phosphatase (ALP), up to 4 times normal, due to secretion by the placenta
5) Reduced albumin due to loss of proteins in the kidneys
6) Calcium requirements increase, but so does gut absorption of calcium, meaning calcium levels remain stable

Question 16

Describe some skin and hair changes that occur during pregnancy

Answer 16

1) Increased skin pigmentation due to increased melanocyte stimulating hormone, with Linea nigra and melasma
2) Striae gravidarum (stretch marks on the expanding abdomen)
3) General itchiness (pruritus) can be normal, but can indicate obstetric cholestasis
4) Spider naevi
5) Palmar erythema