Maternal Physiology in pregnancy and labour

Question 1

Weight gain in pregnancy

Answer 1

Should be no more than 10-12kg

3.5 fat, 0.4 breasts, 1 uterus, 1.3 blood, 3.4 fetus, 0.7 placenta, 0.8 amniotic fluid, 1.5-4.5 extracellular water

Question 2

Plasma volume in pregnancy

Answer 2

Between 1L minimum and 2.5L in quadruplets

Multigravid women will increase more than primigravid

Question 3

Red blood cell changes in pregnancy

Answer 3

Synthesis is increased due to EPO –> increased No. but dilutional anaemia (Haematocrit 40%–>32%) - increases depends on Fe supplements
30% increase in intracellular 2,3 DPG which facilitates O2 offloading

Question 4

Nutrient changes in pregnancy

Answer 4

Goes up: Triglycerides, phospholipids, cholesterol, copper, carotenoids, glycerol,
Goes down:Vit A, Ca, Mg, glucose, amino acids, Fe, Zinc, albumin, Vit B12, Vit B6, Folate,

Question 5

The process of placentation

Answer 5

Trophoblast invasion –> uterine artery remodelling
This leads to low resistance in the uteropalcental circulation and high blood flow to the placenta
In pre-eclampsia or IUGR the arterial remodelling doesnt reach the myometrium so there is limited blood flow to the placenta

Question 6

Uterine artery doppler

Answer 6

Should always be positive flow –> in abnormal pregnancies the flow is more similar to the non-pregnant state where there is little to no flow in diastole

Question 7

Functions of the placenta (5)

Answer 7

Respiratory organ
Nutrient transfer and excretion
Hormone synthesis
Drug transfer and metabolism
Immune protection

Question 8

Placental transport mechanisms (6,8)

Answer 8

Passive (simple or facilitated diffusion) for water, O2, CO2, Na, K & urea
Active (carrier mediated) for glucose, amino acids, polysaccarides, proteins, fats, iron, Vit B & C and antibodies

Question 9

Respiratory functions of the placenta

Answer 9

Maternal PO2 is 90-100mmHg while fetal is 30-40mmHg
Placenta consumes alot itself
Acid/base balance is regulated by passive diffusion

Question 10

Nutrient transfer and excretion

Answer 10

Carrier mediated transport but complex molecules are broken down and reconstituted by the chorionic villi
Fetal energy is 90% from glucose and 10% from amino acids –> excess is stored as glycogen

Question 11

Movements of drugs across the placenta

Answer 11

Most drugs cross the placenta and into breast milk
Speed of passage controlled by size, solubility and charge
Warfarin & anticonvulsants are teratogenic
Alcohol etc can also cross the placenta

Question 12

Immune functions of the placenta

Answer 12

The fetus is a semi-allograft --> trophoblast expresses class I MHC to prevent recognition by maternal immune system
Failure to do this may lead to recurrent miscarriage

Question 13

Fetoplacental hormones (4)

Answer 13

Lots, including:

Neuropeptides, pituitary hormones, steroid hormones and adrenal peptides

Question 14

Steroid creation in pregnancy

Answer 14

3 compartments (fetal, placental and maternal)
The placenta makes progesterones and estrogens from cholesterol which is released into the maternal circulation --> some of the synthesis occurs in the fetus

Question 15

Role of estrogens in pregnancy

Answer 15

Made in the placenta and increase over the pregnancy. Responsible for: CVS adaptsion, growth of the uterus & priming of it for labour, weak anti-insulin, some impact on cervical ripening

Question 16

Role of progesterone in pregnancy

Answer 16

Made in the corpus luteum then placenta and increases over pregnancy.prepares endometrium for implantation, maintainance of pregnancy by blocking uterine contraction and cervical ripening, immunosuppressive, substrate for fetal adrenal hormone production, induces overbreathing to reduce CO2, breast growth

Question 17

Human chorionic gonadotropin (HCG)

Answer 17

Spikes at 8wks then drops off by 20wk
Maintains the function of the corpus luteum until the placenta can take over at 6th week
stimulates the maternal thyroid by binding to TSH or LH receptors

Question 18

Human placental lactogen (HPL)

Answer 18

Produced from 10wks and increases until term
Causes maternal lipolysis to increase FFAs + diabetogenic action. Potent angiogenic effect which may be important in forming fetal vasculature

Question 19

Role of CRH in pregnancy

Answer 19

Increases from 60 days before birth (+decrease in CRH BP). thought to be involved in the initation of parturition –> increases prostaglandin formation in the placenta, amnion and decidua (placental clock?)

Question 20

Role of leptin in pregnancy

Answer 20

Secreted by trophoblast cells making maternal levels much higher –> stimulates placental amino acid and fatty acid transport.
Fetal lepin plays a role in development and growth —> strongly correlates with birth-weight

Question 21

The thyroid gland in pregnancy

Answer 21

Increased iodine uptake and follicular hyperplasia
Total T3 and T4 rise but free levels are unchanged
In part due to hCG stimulation in early pregnancy

Question 22

Cardiovascular changes in pregnancy

Answer 22

CO and HR significantly increase

TPR, BP and haematocrit decreases

Question 23

Causes of fluid retention in pregnancy

Answer 23

Oestrogen activates the renin-angiotensin system
Progesterone increases aldosterone
Shunting of blood to uterus activates sympathetics
Na loss due to increased GFR increases Renin
hCG also increases Renin

Question 24

Renal function in pregnancy

Answer 24

Plasma markers (urea and creatinine) decrease due to dilution. May have glycosuria, calciuria, increased frequency and urinary stasis
GFR and renal plasma flow increasse until 26wk (80%) and then falls back to 150% by term

Question 25

Pulmonary function in pregnancy

Answer 25

Tidal volume increases and gravid uterus mainly reduces residual. progesterone stimulates overbreathing to reduce CO2–> HCO3 falls to compensate
RR unchanged but expiratory reserve reduced

Question 26

Coagulation and fibrinolysis in pregnancy

Answer 26

Increase in factors VII,VIII and X.
Increase in fibrinogen leading to increased ESR
Fibrinolytic activity is reduced
Mild increased in coagulability

Question 27

Gastrointestinal changes in pregnancy

Answer 27

Reduction in smooth muscle tone
Decreased motility & cardiac sphincter tone
Increased Billary stasis, reflux, nutrient & water absorption

Question 28

ECG changes in pregnancy

Answer 28

Typical changes include a frontal shift in the QRS axis, and small Q wave and an inverted T wave in lead III

Question 29

Stages of labour

Answer 29

First stage which has both latent and active components
Second stage ending in birth
Third stage while the placenta is delivered

Question 30

First (Latent) stage of labour

Answer 30

Contractions start and the cervix dilates up to 3cm

Question 31

First (Active) stage of labour

Answer 31

Regular contractions steadily dilate the cervix to 10cm

Question 32

Second stage of labour

Answer 32

With the cervix fully effaced the fetus is delivered with strong, voluntary propulsive contractions
Usually takes no more than 1-2hrs

Question 33

Third stage of labour

Answer 33

Placenta delivered

Shit stage really

Question 34

What causes the cervix to ripen?

Answer 34

Progesterone withdrawal leads to inflammation and an influx of immune cells. CRH and oestrogen also play a role. Once this has begun oxytocin starts a positive feedback mechanism (Ferguson reflex)

Question 35

What prepares the myometrium for labour?

Answer 35

CRH, Oxytocin and oestrogen + uterine distension
Progesterone withdrawal leads to inflammation and an influx of immune cells –> induces contraction associated proteins, prostaglandin+oxytocin receptors, Ca signalling proteins, gap junctions and ion channels

Question 36

Role of Oxytocin in labour

Answer 36

An important uterotonin in labour
During labour there is an increase in uterine sensitivity to oxytocin and increased expression of the oxytocin receptor and mRNA

Question 37

Timing of labour

Answer 37

Tightly controlled with 80-90% occuring between 36 and 42wks

Black and asian women tend to labour slightly earlier then white people

Question 38

What initiates labour?

Answer 38

For animals its a drop in progesterone but in humans there is no drop, most likely a functional progesterone withdrawal

Question 39

Milk production from the breast

Answer 39

lobules and alevoli grow during pregnancy to make more milk producing cells –> able to produce milk from 16 weeks but lactation blocked until partum
Milk contains 750Kcal/L, 38g lipids/L, 70g lactose/L

Question 40

What controls lactation?

Answer 40

At birth there is a sudden drop off of Progesterone and estrogen and HPL with a slower decrease in prolactin –> steroids have been blocking prolactin effects on breast, suckling maintains prolactin release leading to milk production

Question 41

How does suckling ensure milk production?

Answer 41

A neuroendcrine reflex decreases dopamine and increases VIP in the pituitary portal circulation increasing prolactin secretion
The same process causes oxytocin release which causes myoepithelial contraction causing milk ejection reflex (MER)

Question 42

What processes ripen the cervix?

Answer 42

iNOS and matrix metalloproteinases 2 and 9

Cox-2 enzymes and cytokines produce prostaglandins

Question 43

WCC in pregnancy

Answer 43

Can be raised physiologically in pregnancy