Maternal Physiology, Pregnancy And The Placenta

Question 1

What are the broad changes that occur to maternal physiology during pregnancy?

Answer 1

Vasodilation, increased respiratory rate, increased insulin resistance and absorption from the gut, increased GFR, immunological sequestration, increased clotting and relaxation of muscles.

Question 2

How does the immune system change to facilitate pregnancy?

Answer 2

Placental progesterone acts upon extravillus trophoblastic cells to cause IL10 release from TR1 cells that mediate suppressive activity of the immune system. As such, immune responses produced to the foetus are TH2 and non cytotoxic

Question 3

How does ventilation increase in pregnancy?

Answer 3

Increase in tidal volume by 30-40%. Note that there should not be an increase in respiratory rate, and this is indicative of pathology.

Question 4

Why does dyspnea occur in 65% of pegnancies?

What factors may exacerbate this?

Answer 4

Hyperventilation due to increased tidal volume resulting in low PaCO2.
Anaemia,
Asthma,
DVT/PE (high risk during pregnancy)

Question 5

What adaptations occur in the CVS during pregnancy?

Answer 5

Increased cardiac output due to increased volume early in pregnancy and increased heart rate later in pregnancy.
Vasodilation aided by smooth muscle relaxing effects of progesterone.
Increased procoagulants, decreased anticoagulants and reduced fibrinolysis.

Question 6

What are the (negative) consequences of the CVS adaptations of pregnancy?

Answer 6

Increased activation of RAAS causing peripheral oedema.
Change in plasma volume resulting in dilutational anaemia.
Hyper coagulase state - risk of DVT and thromboembolism.

Question 7

How is GFR increased by 50% during pregnancy?

What other effects occur in the kidney?

Answer 7

Systemic vasodilation increases renal blood flow.
Decreased PCT absorption of glucose - glucosuria.
Smooth muscle relaxation - increased kidney and ureter size and decreased urine speed.

Question 8

How is transit time slowed in the GI system?

What hormone mediates these changes?

Answer 8

Decreased motility of bowel, decreased gallbladder contractility, decreased tone of the lower oesophageal sphincter.
Progesterone.

Question 9

What negative effects may result from the adaptations made to the GI system?

Answer 9

GORD, constipation, gallstones, aspiration.

Question 10

Why may ALP levels be raised on LFTs during pregnancy?

Answer 10

Placental synthesis results in release of ALP.

Question 11

What occurs in the thyroid during pregnancy?

Answer 11

Oestrogen stimulates thyroglobulin production by the liver that picks up free thyroxine. HCG has a stimulatory effect on thyroid due to similar alpha subunit to TSH. As such, it stimulates production of T4 and T3.
Note: the foetus cannot produce its own thyroid hormones.

Question 12

How does pregnancy influence the function of the parathyroid gland?

Answer 12

Increased PTH secretion acting upon the pathway of vitamin D activation and inhibiting the Ca phosphorus resorption pathway. This results in greater amounts of calcium absorbed from the GI tract.

Question 13

Which hormones found in pregnancy have effects on insulin resistance?

Answer 13

hPL (most prominent),
Oestrogen,
Progesterone.

Question 14

What factors when alongside pregnancy may result in defective action of insulin?

Answer 14

Physical inactivity,
Obesity,
PCOS,
Hypertension.

Question 15

What is gestational diabetes mellitus?

Answer 15

Onset of elevated blood sugar levels during pregnancy. Increased maternal mortality and morbidity for both mother and child.

Question 16

What adaptions occur to the MSK system during pregnancy?

Answer 16

Change in center of gravity, increased lordosis and kyphosis, stretching of abdominal muscles,
Increased mobility of sacroiliac joints and anterior tilt of pelvis.

Question 17

What negative effects may changes in the MSK system have?

Answer 17

Back pain, shoulder pain, tension headaches, Pelvic pain, fluid retention compression of structures eg carpal tunnel.

Question 18

What features may be seen on the skin of pregnant women?

Answer 18

Chloasma or melasma of the face, palmar erythema, vascular spiders, linea nigra.

Question 19

What is preeclampsia?

Answer 19

Defined as combination of new hypertension and proteinuria seen in pregnancy. thought to result due to impaired invasion of trophoblast resulting in shallow spiral arteries and higher resistance. May lead to hypoperfusion and ischaemia.

Question 20

Name risk factors of preeclampsia.

Answer 20

Hypertension,
Diabetes,
Obesity,
First pregnancy.

Question 21

What complications of preeclampsia are there?

Answer 21

Seizure (eclampsia), cerebral haemorrhage, pulmonary oedema, premature delivery, stillbirth, growth restriction, foetal distress.

Question 22

When does the placenta begin to develop?

What aids in its hormonal role until it is formed?

Answer 22

Second week of development,

Corpus luteum.

Question 23

What occurs during the week of twos?

Answer 23

Outer cell mass diverges into syncytiotrophoblast and cytotrophoblast.
Inner cell mass diverges into epiblast and hypoblast.
Syncitiotrophoblast begins secretion of hCG

Question 24

What happens to each of the embryonic spaces as pregnancy continues?

Answer 24

Yolk sac pinches off to form part of the primitive gut.

Amniotic sac enlarges to occupy the chorionic cavity - causes chorionic sac to disappear.

Question 25

Why does the placental membrane become progressively thinner as pregnancy continues?

Answer 25

Demand of the foetus for nutrients grows so a more efficient diffusion/transport pathway is required.
Note: maternal and foetal circulations never mix.

Question 26

What is the placenta formed from?

Answer 26

Chorionic membrane. Forms chorion frondosum - fern shaped projections that increase surface area for exchange.

Question 27

How is invasion of the embryo controlled?

Answer 27

The decidual layer of the endometrium exerts a resistant effect to the syncitiotrophoblasts digestive enzymes, meaning implantation occurs at a correct depth.

Question 28

What is the functional unit of the placenta?

Answer 28

Cotyledon - contain chorionic villi within thin membranes to facilitate diffusion. Highly vascular.

Question 29

What facilitates the thinning of the barrier between the chorionic villi and maternal blood supply?

Answer 29

Loss of the cytotrophoblastic layer.

Question 30

What fetal vessels supply the placenta?

Answer 30

Two umbilical arteries carrying deoxygenated blood from foetus to placenta.
One umbilical vein supplying oxygenated blood from the placenta to the foetus,

Question 31

What steroid hormones are produced by the placenta?

Answer 31

Oestrogen and progesterone.

Question 32

What protein hormones are produced by the placenta?

Answer 32

HCG,
hPL,
Human chorionic thyrotrophin,
Human chorionic corticotrophin.

Question 33

where might HCG be raised?

Answer 33

Molar pregnancy (tumour of the placenta leading to growth of placenta without embryo).
Choriocarcinoma.
Prostate cancer in men.

Question 34

How do placental hormones influence maternal metabolism?

Answer 34

Progesterone - increases appetite

hCS or hPL - increases glucose availability to the fetus

Question 35

Which molecules diffuse freely through the placental barrier?

Answer 35

Water, gases, electrolytes, urea.

Question 36

What must move via facilitated transport into the fetal blood supply?

Answer 36

Glucose

Question 37

Why is gas exchange especially important in the foetus?

When might exchange be occluded?

Answer 37

Fetal oxygen stores are very limited with high demand. As such gas exchange is flow limited.
May become occluded during contractions - causes foetal distress.

Question 38

Which molecules are actively transported by transporters expressed in the syncitiotrophoblast?

Answer 38

Amino acids, iron and vitamins.

Question 39

How are IgG antibodies transferred from mother to fetus?

Answer 39

Receptor mediated exo and endocytosis

Question 40

What can cause haemolytic disease of the newborn?

What test can be done to confirm this?

Answer 40

Transfer of IgG antibodies to a different Rhesus group blood cell type to the fetus.
Group and save

Question 41

What teratogens may cross the placenta?

Answer 41

Thalidomide,
Alcohol,
Antiepileptics,
Warfarin,
ACE inhibitors.

Question 42

What infections can cross the placenta?

Answer 42

Varicella zoster (also increased risk during pregnancy), TB, cytomegalovirus, Rubella virus.