Physiology of Pregnancy

Question 1

Structure of hCG

what it is produced by

Answer 1

Two chain hormone, with the alpha chain the same as TSH, LH and FSH
Produced by STB of placenta and trophectoderm of preimplantation blastocyst

Question 2

How is BhCG used?

Answer 2

To detect pregnancy by urine or blood if need be

levels raise to about 10 weeks gestation, then start to drop

Question 3

Function of b hCG

important for maintaining pregnancy!

Answer 3

Transmits signals similar to LH

Causes the corpus luteum to produce progesterone and estrogen in the first 6-8 weeks. Prevents regression, and size will double.

After 6-8 weeks, placenta takes over as main source of progesterone, so hCG function is to keep uterus from returning to normal cyclic pattern by keeping CL producing P and E

Question 4

hCG and cancer
hCG and male sexual diff
thyroid

Answer 4

Cancer: levels can be monitored in things like choriocarcinoma and hyaditiform mole

Sex diff.: hCG targets leydig cells prior to pituitary development to produce testosterone

Thyroid: similar to TSH, can stimulate thyroid hyperthyroidism

Question 5

Progesterone:
Synthesis
Fetus role
Receptor location
Concentration on graph

Answer 5

Synthesis: STB (thus in cancers present). Can not from from acetate so use LDL from circulation (LDL receptors)

Fetus: Does not partake in production. (note ovaries can be removed after 6 weeks)

Receptor location: Endometrial glands and stroma

On graph, slight increase (CL) then after 10 weeks steady increase

Question 6

Function of progesterone

Answer 6

• Maintain uterine quiescence (relaxes myometrium)
• Along with oestrogen, provide uterine environment adapt for pregnancy
• induces decidual formation (remember decidua not necessary for implantation) and maintains

Question 7

What requirements are there for oestrogen production in pregnancy?

note 1000 fold increase during pregnancy

Answer 7

1) Live fetus
2) Fetal adrenals functioning
3) intact feto-placental circulation
4) functioning placenta

Question 8

Why can’t the placenta make estrogen?

Answer 8

It does not contain the enzyme 17 alpha hydroxylase
(moles and choriocarcinomas can not produce)
However can aromatise testosterone, just can not form androgens

Question 9

How are oestrogens made in pregnancy?

Answer 9

Placenta makes progesterones, which travel into fetal circulation.
In the fetal adrenals and liver, these are converted to androgens
Androgens travel back in fetal circulation to the placenta
Are aromatised in the STB into free oestrogens which are secreted in maternal blood

Question 10

What can be said about the STB and steroid production/release?

Answer 10

Most oestrogens and progesterone end up in maternal circulation due to close contact.

However maternal blood to fetus is a longer distance

Question 11

What is preeclampsia?

Answer 11

A dangerously elevated maternal blood pressure associated with proteinurea or multiorgan dysfunction.

Affects most maternal organs; only in pregnancy; triggered by placenta; inflammatory response leading to vascular failure; normal vasculature fails to adapt, typically vasculature relaxes, so in this, higher peripheral resistance

Question 12

What are the cardiovascular adaptations to pregnancy?

when do they occur?

Answer 12

Increase cardiac ouput (10% SV and 10-15% HR); starts early in gestation
Reduced peripheral vascular resistance to compensate for increased BP (if it does not preeclampsia?)

9 weeks

Question 13

What causes the CV change in pregnancy (4 hormones)

NB idea of placental vesicles preventing endothelial cll activation

Answer 13

Oestrogen: Reduces vascular resistance; changes ratio of type 1 and 3 collagen in vessel wall. However fetal adrenals not making much at 9 weeks

Progesterone: may induce vascular relaxation in the placenta only. However low at 9/10 weeks also

Angiotensin: uteroplacental unit produces a lot, vasoconstricting effect. However effect is blunted in pregnancy

NO: made by endothelium. Nitric oxide synthetase activity is increased in some tissues in preg

Question 14

What are the haemotological changes in pregnancy?

Answer 14

An increase in blood volume. the plasma increases at a much faster rate (1250 mL on average), resulting in a declining haemotocrit. (note this occurs after the CV changes, as increase in CO preceeds the volume change, showing it is not more blood that needs pumping around). Stable at 30 weeks

Question 15

Lecture take home message

Answer 15

Pregnancy is a physiological state, not a disease. When looking at results check the normals for pregnancy not the standard norms

Question 16

What is the purpose of the haematological change?

Answer 16

During delivery loss of 500mL roughly of blood.

The hypervolaemia accounts for this. Haemtocrit retuns slowly

Question 17

How does the immune system adapt in pregnancy?

Answer 17

*- Seminal plasma dulls effects of immune response (immunosuppressive to a degree) tolerises to a degree

• some evidence of immune diminuition in pregnancy to some organisms meaning first encounter infection dealt with poorly
• Increase in white cell count, due to luteal phase, does not stop. Neutrophils peak at 30 weeks, then rise at labour.
• lymphocyte count does not change, bias towards TH2 cells, that drive towards antibody mediated response

Question 18

What is special about the decidua’s immune system?

Answer 18

• No B cells and resident T cell population
• Has uterine NK cells. NK cells produce antibody dependent cell mediated cytotoxicity
• uNK cells lack the CD16, and instead produce growth factors

Question 19

How does the uterus grow during pregnancy?

Answer 19

Growth is attributed to cell stretching.

Cell length goes from 50 microns to 400-600 microns

Question 20

Cervical change during pregnancy

Answer 20

Softens and glands form to make up half the mass.
Water and GAG’s increase, collagen is lost.
Incompetent cervix associated with recurrent miscarriage

Question 21

How does uteroplacental blood flow change during pregnancy

Answer 21

• First trimester: very limited due to trophoblast plugs (so as to make spiral arteries eroded, and have no tone). Remains like this for up to 10 weeks
• At about 13 weeks, flow into intervillous spaces can be recorded. Increases all the way up to term (10 weeks 50, 28 week 185, term 500-700)

Question 22

Changes to abdominal wall and skin

Answer 22

Increased blood flow to skin, hands (peripheries)
Clammy hands
Skin pigmentation changes: Nipple and areola; linea nigra (belly); chloasma;
Hair loss reduced in pregnancy, but is then lost afterwards