Maternal Physiology in pregnancy and labour Flashcards
Weight gain in pregnancy
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
Plasma volume in pregnancy
Between 1L minimum and 2.5L in quadruplets
Multigravid women will increase more than primigravid
Red blood cell changes in pregnancy
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
Nutrient changes in pregnancy
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,
The process of placentation
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
Uterine artery doppler
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
Functions of the placenta (5)
Respiratory organ Nutrient transfer and excretion Hormone synthesis Drug transfer and metabolism Immune protection
Placental transport mechanisms (6,8)
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
Respiratory functions of the placenta
Maternal PO2 is 90-100mmHg while fetal is 30-40mmHg
Placenta consumes alot itself
Acid/base balance is regulated by passive diffusion
Nutrient transfer and excretion
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
Movements of drugs across the placenta
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
Immune functions of the placenta
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
Fetoplacental hormones (4)
Lots, including:
Neuropeptides, pituitary hormones, steroid hormones and adrenal peptides
Steroid creation in pregnancy
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
Role of estrogens in pregnancy
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
Role of progesterone in pregnancy
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
Human chorionic gonadotropin (HCG)
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
Human placental lactogen (HPL)
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
Role of CRH in pregnancy
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?)
Role of leptin in pregnancy
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
The thyroid gland in pregnancy
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
Cardiovascular changes in pregnancy
CO and HR significantly increase
TPR, BP and haematocrit decreases
Causes of fluid retention in pregnancy
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
Renal function in pregnancy
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
Pulmonary function in pregnancy
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
Coagulation and fibrinolysis in pregnancy
Increase in factors VII,VIII and X.
Increase in fibrinogen leading to increased ESR
Fibrinolytic activity is reduced
Mild increased in coagulability
Gastrointestinal changes in pregnancy
Reduction in smooth muscle tone
Decreased motility & cardiac sphincter tone
Increased Billary stasis, reflux, nutrient & water absorption
ECG changes in pregnancy
Typical changes include a frontal shift in the QRS axis, and small Q wave and an inverted T wave in lead III
Stages of labour
First stage which has both latent and active components
Second stage ending in birth
Third stage while the placenta is delivered
First (Latent) stage of labour
Contractions start and the cervix dilates up to 3cm
First (Active) stage of labour
Regular contractions steadily dilate the cervix to 10cm
Second stage of labour
With the cervix fully effaced the fetus is delivered with strong, voluntary propulsive contractions
Usually takes no more than 1-2hrs
Third stage of labour
Placenta delivered
Shit stage really
What causes the cervix to ripen?
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)
What prepares the myometrium for labour?
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
Role of Oxytocin in labour
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
Timing of labour
Tightly controlled with 80-90% occuring between 36 and 42wks
Black and asian women tend to labour slightly earlier then white people
What initiates labour?
For animals its a drop in progesterone but in humans there is no drop, most likely a functional progesterone withdrawal
Milk production from the breast
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
What controls lactation?
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
How does suckling ensure milk production?
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)
What processes ripen the cervix?
iNOS and matrix metalloproteinases 2 and 9
Cox-2 enzymes and cytokines produce prostaglandins
WCC in pregnancy
Can be raised physiologically in pregnancy
