8. Pregnancy

Question 1

What does implantation involve?

Answer 1

Interaction between trophoblast cells and epithelium of the uterus. Embedding of the blastocyst into the endometrium depending on invasive property of trophoblasts with outer layer synctiotrophoblast and underlying cytotrophoblast.

Question 2

What is meant by implantation being interstitial?

Answer 2

Uterine epithelium is breached and conceptus implants within the stroma.

Question 3

What happens to the placental membrane through pregnancy?

Answer 3

It gets thinner as the needs of the foetus increase.

Question 4

What is meant by the placenta being haemomonochorial?

Answer 4

One layer of trophoblast separates maternal blood from foetal capillary wall.

Question 5

What are the aims of implantation?

Answer 5

Establish the basic unit of exchange, anchor the placenta, establish maternal blood flow within the placenta.

Question 6

What makes up the basic unit of exchange in implantation?

Answer 6

Primary villi - early, finger-like projections of trophoblast.
Secondary villi - invasion of mesenchyme into core.
Tertiary villi - invasion of mesenchyme core by foetal vessels.

Question 7

How is the placenta anchored in implantation?

Answer 7

Establishment of outermost cytotrophoblast shell.

Question 8

What are the two key features of the histology of the endometrium in preparation for implantation?

Answer 8

Decidualisation and remodelling or spiral arteries.

Question 9

What is decidualisation in implantation preparation?

Answer 9

Pre-decidual cells, decidual reaction provides balancing force for invasive force of trophoblast, stimulated by progesterone.

Question 10

What is remodelling of spiral arteries in implantation preparation?

Answer 10

Creation of low resistance vascular bed, maintains high flow required needed to meet foetal demand, particularly in late gestation.

Question 11

What are the possible implantation defects?

Answer 11

Ectopic pregnancy - implantation at site other than uterine body, usually fallopian tube although it can be peritoneal or ovarian.
Placenta praevia - implantation in lower uterine segment.
Incomplete invasion - placental insufficiency -> pre-eclampsia.

Question 12

What is the structure of the placenta by the beginning of the fourth month?

Answer 12

Foetal portion - formed by chorion frondsum and bordered by chorionic plate.
Maternal portion - formed by decidua basalis.
Space between (intervillous spaces) - filled with maternal blood.

Question 13

What happens in the fourth and fifth months to the decidua?

Answer 13

It forms a number of decidual septa which project into intervillous space but don’t reach chorionic plate. They divide the placenta into cotyledons.

Question 14

What is the first trimester placenta like?

Answer 14

Placenta is established, it’s a barrier to diffusion as still relatively thick, complete cytotrophoblast layer beneath the synctiotrophoblast.

Question 15

What is the full term placenta like?

Answer 15

Surface area for exchange dramatically increased, barrier is now thin - cytotrophoblast layer beneath synctiotrophobalst lost.

Question 16

What are the foetal blood vessels within the placenta?

Answer 16

Two umbilical arteries (deoxygenated blood from foetus to placenta) and one umbilical vein (oxygenated blood from placenta to foetus).

Question 17

Where do the cotyledons receive blood from?

Answer 17

Through 80-100 spiral arteries that pierce the decidual plate.

Question 18

What is the role of spiral arteries?

Answer 18

Pressure forces oxygenated blood deep into intervillous spaces and bathe numerous small villi in the villous tree in oxygenated blood. Pressure decreases so blood flows back from chorionic plate to decidua to enter endometrial veins.

Question 19

What are the factors that influence passive diffusion of substance across the placenta?

Answer 19

Concentration gradient - steeper gradients means more diffusion.
Barrier to diffusion - placental membrane gradually thins throughout pregnancy as demands of foetus increases.
Diffusion distance - haemomonochorial.

Question 20

Which substances can transport across the placenta by simple diffusion?

Answer 20

Water, electrolytes, urea and uric acid, gases.

Question 21

Which substance can transport across the placenta by simple diffusion?

Answer 21

Glucose.

Question 22

Which substances can transport across the placenta by active transport?

Answer 22

Amino acids, iron, vitamins by specific transporters expressed by syncytiotrophoblast.

Question 23

In what dangerous way is the placenta not a true barrier?

Answer 23

Teratogens can cross it and damage the foetus.

Question 24

What are some teratogens?

Answer 24

Thalidomide, alcohol, therapeutic drugs, drugs of abuse, maternal smoking.

Question 25

What pathogens can cross the placenta and which diseases do they cause?

Answer 25

Varicella zoster -> shingles, cytomegalovirus -> herpes, treponema pallidum -> syphilis, toxoplasma gondii -> toxoplasmosis, rubella -> German measles.

Question 26

What are the protein hormones produced by the placenta?

Answer 26

Human chorionic gonadotrophin, human chorionic somatommotrophin, human chorionic thyrotrophin, human chorionic corticotrophin.

Question 27

What is the role of hCG?

Answer 27

Supports secretory function of corpus luteum.

Question 28

Why can hCG be measured to indicate pregnancy?

Answer 28

It’s made in the first two months of pregnancy by the syncytiotrophoblast which is specific to pregnancy. It is secreted in maternal urine so easily measured.

Question 29

What is the role of hCG?

Answer 29

Influences maternal metabolism so there is more glucose available for the foetus.

Question 30

What are the steroid hormones produced by the placenta?

Answer 30

Progesterone and oestrogen.

Question 31

What are the roles of steroid hormones from the placenta in pregnancy?

Answer 31

Maintain pregnancy state. Progesterone influences maternal metabolism by increasing appetite.

Question 32

Apart from protein and steroid hormones, what does the placenta synthesise?

Answer 32

Glycogen, cholesterol, and fatty acids.

Question 33

When does immunological competence begin to develop?

Answer 33

In the first trimester, the foetus makes all the components of complement.

Question 34

When is maternal immunoglobulin transported to the foetus?

Answer 34

At around 14 weeks.

Question 35

How is IgG transported to the foetus in pregnancy?

Answer 35

Via receptor mediated pinocytosis.

Question 36

When are adult levels of IgG attained post birth?

Answer 36

Aged 3.

Question 37

Explain the pathophysiology of haemolytic disease of the newborn.

Answer 37

Rhesus blood group incompatibility of mother and foetus. The mother has been previously sensitised to rhesus antigen from a previous pregnancy. IgG against rhesus crosses the placenta and attacks the foetal RBCs.

Question 38

Why is haemolytic disease of the newborn uncommon now?

Answer 38

Prophylactic treatment given to a rhesus negative mother pregnant with a rhesus positive foetus to prevent sensitisation in the event of exposure to the antigen.

Question 39

What are the physiological cardiovascular system changes in pregnancy?

Answer 39

Blood volume increases, cardiac output increases, stroke volume increases, heart rate increases. Systolic BP shouldn’t increase as systemic vascular resistance decreases enough to outweigh other changes.

Question 40

What is hypotension in pregnancy due to?

Answer 40

Progesterone effects on systemic vascular resistance.

Question 41

Why does BP return to normal in the third trimester?

Answer 41

Aortocaval compression by gravid uterus reduces return to the heart.

Question 42

What are the physiological urinary system changes in pregnancy?

Answer 42

Renal plasma flow increases, glomerular filtration rate increases, filtration capacity stays intact, functional renal reserve decreases.

Question 43

Why is urinary stasis potentially a problem in pregnancy?

Answer 43

Progesterone relaxes the smooth muscle in walls of the ureters which can causes stasis, hydroureter, UTIs, or pyelonephritis. Pyelonephritis can induce pre-term labour.

Question 44

What are the physiological respiratory system changes in pregnancy?

Answer 44

Diaphragm is displaced but the AP and transverse diameters of the thorax increase. So O2 consumption increases by 20%, functional residual capacity decreases, vital capacity is the same, tidal volume increases, respiratory minute volume increases, alveolar ventilation rate increases, respiratory rate is unchanged.

Question 45

What causes physiological hyperventilation in pregnancy?

Answer 45

Progesterone drive it causing the mother to blow off the extra CO2 that the foetus produces.

Question 46

How does the mother’s body respond to physiological hyperventilation in pregnancy?

Answer 46

Respiratory alkalosis means the kidneys respond by producing and reabsorbing less HCO3-.

Question 47

What are the physiological carbohydrate metabolic changes in pregnancy?

Answer 47

Glucose and amino acid metabolism are altered to favour nutritional supply to the foetus. Fat is laid down in the first half of pregnancy to meet the later demands of the foetus. Progesterone stimulates appetite in the first half and changes glucose into fat synthesis. Oestrogen stimulates increase prolactin increase to cause maternal resistance to insulin leading to less glucose usage by the mother and more gluconeogenesis, maximising availability of glucose to foetus. Mother’s energy needs are met later by metabolising peripheral fatty acids.

Question 48

How is glucose transported to the foetus?

Answer 48

Across the placenta by facilitated diffusion.

Question 49

What is gestational diabetes?

Answer 49

Carbohydrate intolerance first recognised in pregnancy and not persisting after delivery.

Question 50

What are the risks associated with poor control of gestational diabetes?

Answer 50

Macrosomic foetus, stillbirth, increased risk of congenital defects.

Question 51

What is the pathophysiology of gestational diabetes?

Answer 51

Maternal insulin secretion rate usually increases as pregnancy proceeds. The pancreatic B-cells meet the demand with B-cell hyperplasia and hypertrophy as well as increased rate of insulin synthesis in the B-cell. In some women, the pancreas can’t respond to the increased demand so there isn’t enough insulin -> loss of control of metabolism -> diabetes.

Question 52

What happens to women with gestational diabetes after childbirth?

Answer 52

Metabolic demands of pregnancy are removed and hormone levels change so the endocrine pancreas responds adequately and diabetes disappears.

Question 53

What are the physiological changes to lipid metabolism in pregnancy?

Answer 53

Increased lipolysis from T2 so increased fatty acid concentration on fasting - substrate for maternal metabolims.

Question 54

What is a risk with increased use of fatty acids in pregnancy?

Answer 54

Ketoacidosis, which combined with compensatory respiratory alkalosis.

Question 55

What are the physiological changes to the thyroid in pregnancy?

Answer 55

Thyroid binding globulin production increases, T3 and T4 increase but T4 stays within the normal range from increased binding globulin. hCG has an effect on the thyroid meaning T3/4 production is stimulated. TSH is decreased due to negative feedback.

Question 56

What are the physiological changes to the gastrointestinal system in pregnancy?

Answer 56

Anatomical changes - alterations in positions of viscera, e.g. appendix moves from RLQ to RUQ as uterus enlarges.
Physiological changes - smooth muscles relaxation by progesterone leads to delayed emptying in GI tract, stasis in biliary tract, and increased risk of pancreatitis.

Question 57

What are the physiological changes to the haematological system in pregnancy?

Answer 57

Pregnancy is a pro-thrombotic state - high amount of fibrin at site of implantation (increased fibrinogen and clotting factors, decreased fibrinolysis), stasis and venodilation -> thromboembolic disease in pregnancy.
Anaemia due to increase in plasma volume. RBC mass also increase but not to the same degree => physiological anaemia from mismatch or from iron/folate deficiency.

Question 58

What are the physiological changes to the immune system in pregnancy?

Answer 58

Foetus is an allograft so there is non-specific suppression of the local immune response at materno-foetal interface. Also transfer of antibodies (IgG or rhesus, can also stimulate TSH receptors of destroy developing foetal thyroid -> Graves or Hashimoto’s).

Question 59

What is involved in antenatal screening?

Answer 59

History and examination, blood test, urinalysis.

Question 60

How is a pre-eclamptic pregnancy different to a normal pregnancy?

Answer 60

Vasoconstricted instead of vasodilated, plasma contracted instead of plasma expanded, raised blood pressure vs blood pressure lowered or normal, proteinuria, and pitting oedema.