Obstetric Physiology Flashcards
What is the placenta formed from?
Trophoblast
What happens to the placenta at day 6 of gestation?
Trophoblast interact with endometrial decidual epithelia –> invasion into maternal uterine cells
Invasion is interstitial and on the anterior and posterior walls of the body of the uterus
What happens to the placenta at day 8 of gestation?
Differentiation into syncitiotrophoblast and cytotrophoblast
Syncitiotrophoblast send out projections to erode maternal tissue and produce HCG
What happens to the placenta at day 9 gestation?
Lacunae form within syncitiotrophoblast and maternal blood enter from spiral arteries
Cytotophoblast begin to form villi
What are the types of villi in the placenta?
Primary - projections of trophoblast
Secondary - invasion of a mesenchyme core
Tertiary - invasion of fetal vessels
What happens to the maternal circulation in the formation of the placenta?
Spiral arteries remodel forming low resistance, high flow circulation
Cytotrophoblast invade the spiral arteries and replace maternal endothelium - 1 less barrier
What are the key blood vessels in the fetus?
Umbilical vein - carry oxygenated blood
Umbilical artery - carry deoxygenated blood
How do nutrients exchange at the placenta?
Maternal O2 and nutrients exchange at terminal villi into intervillous space
What surrounds the fetal surface?
Chorionic membrane:
- amnion
- umbilical vessels
What is the decidua?
Name given to the endometrium which is modified by progesterone in preparation for pregnancy
What are the parts to the Decidua?
Basalis - where the implantation takes place and the basal plate is formed
Capsularis - Capsule around chorion
Parietalis - Lie on opposite uterus wall
What forms the placental barrier in the first trimester?
Syncitiotrophoblast resting on cytotrophoblast
Relatively thick
What is the placental barrier like in the third trimester?
Thin - cytotrophoblast lost
Huge SA
What happens to the placenta around month 4-5?
Decidua form septal which project into intervillous lacunae
Has core maternal tissue and covered by syncitial cells
Septa divide placenta into cotyledons
What is the function of HCG and what secretes it?
Maintain corpus luteum until placenta can secrete the pregnancy hormones
Secreted by syncitiotrophoblast
What causes most maternal adaptations in pregnancy?
Progesterone
Oestrogen has some effect
What changes are seen in pregnancy?
GI Haematological MSK Renal Biochemical Respiratory Nutrient CVS
What GI changes are seen in pregnancy?
Visceral displacement - appendicitis present as RUQ pain
SM relaxation - heartburn + gall stones
Reduced GI motility - constipation
What haematological changes are seen in pregnancy?
Plasma volume increase - dilution anaemia
Raised fibrinogen and clotting factors and decreased fibrinolysis - Pro-thrombotic state
Immunosuppression - risk of infection
What MSK changes are seen in pregnancy?
Ligament laxity - Pubic symphysis dysfunction
Back pain
What renal changes are seen in pregnancy?
Renal plasma flow and GFR increase - increased creatinine and clearance
SM relax - stasis = UTI
Large uterus - Risk of obstruction
Bicarb excretion (compensate for hyperventilation) - low bicarb reserve so acidosis risk
What biochemical changes are seen in pregnancy?
Calcium req. increase - Increased renal excretion (stones) and more GI absorption
TBG increase - free T3/4 = same but overall T3/4 increase for fetal neural development
What respiratory changes occur in pregnancy?
Diaphragm displaced up - AP and transverse diameter increase to compensate
Increased CO2 from fetus and increased respiratory drive - hyperventilation
What nutrient changes are seen in pregnancy?
Raised lactogen, prolactin and cortisol - increased insulin resistance so maternal FA and glucose saved for fetus
Lipolysis to increase FA as metabolic substrate - risk of ketoacidosis
What CVS changes occur in pregnancy?
Increased blood volume
Increased CO, SV. HR
Peripheral resistance and BP drop in 1st and 2nd trimester
IVC compressed if flat on back
How is dyspepsia due to pregnancy managed?
Sleep propped up
Small frequent meals
Decrease spice, fruit, caffeine
Most antacids can be used
How is constipation due to pregnancy managed?
Increase fluid intake
High fibre food
Plenty of exercise
Laxatives
How is fatigue and insomnia due to pregnancy managed?
Rest and reassure
Avoid sleeping tablets
Peak in first trimester
Explain what must be considered when a pregnant lady has pruritus
Look for rash
Exclude obstetric cholestasis - check LFT’s
Common in last 12 weeks
How is back pain due to pregnancy managed?
Light exercise
Simple analgesia
Physio referral
What happens in pubic symphysis dysfunction?
Pain in suprapubic and lower back area which radiates to thigh and perineum
How is pubic symphysis dysfunction managed?
Education
Physiotherapy
Belts
Crutches
Why do pregnant women get carpel tunnel syndrome and how is it managed?
Fluid retention compresses nerve
Wrist splints and steroid injections
What changes are seen in blood results in pregnancy?
Raised - WCC, ALP, TSH (in 3rd trimester)
Lowered - Hb, Na+, K+, Urea, Creatinine, Ca2+, Albumin, Bilirubin, TSH (1st trimester)
When is the uterus usually palpable in the abdomen?
12 weeks
What could cause a large for date uterus?
Molar pregnancy
Multiple pregnancy
Polyhydramnios
Fibroids and Cysts
When does the uterus normally reach the umbilicus?
20 weeks
How long does labour usually last?
8 hours in first pregnancy
5 hours in subsequent pregnancies
How many stages are there to labour?
3
What is the latent first stage of labour?
Painful contractions and
Cervical change - effacement and dilatation upto 4cm
What is the established first stage of labour?
Regular painful contractions AND
Progressive cervical dilatation from 4cm to 10cm
What is considered if the first stage of labour is delayed?
Amniotomy
Oxytocin
What must happen to the cervix in labour?
Dilate
Retract anteriorly
Thin
What triggers cervical changes in labour?
Prostaglandins
What happens to the myometrium in labour?
Pacemaker smooth muscle cells generate AP’s which spread across specialised gap junction –> co-ordinated contractions
What are Braxton-Hicks contractions?
High amplitude, low frequency contractions in third trimester
What is brachystasis in relation to pregnancy?
Uterus contract more than it relaxes meaning fibres shorten progressively - push presenting part into birth canal
When do prostaglandins increase and what are its effects?
Increased levels when oestrogen > progesterone
Ripen cervix
Increase forcefulness of contractions
What is the role of oxytocin in pregnancy?
Increase frequency of contractions
Oxytocin receptors increase when oestrogen > progesterone
What are the parts of the second stage of labour?
Passive
Active
What is the passive second stage of labour?
Finding of full dilatation of cervix before or in absence of involuntary expulsive contractions
What happens in the active second stage of labour?
Baby is visible
Expulsive contractions with full dilatation of cervix
Active maternal effort following confirmation of full dilatation
What movements does the baby do when being delivered?
Head flex Head internally rotate Head delivered Head extend Head externally rotate Shoulders rotate and deliver
When is labour considered delayed?
Active stage lasting:
Nulliparous - >2hr
Multiparous - >1hr
What would you do if labour is delayed?
Refer to obstetrician - operative vaginal delivery
How quickly does the cervix dilate?
> 0.5cm/hr in nulliparous
>1cm/hr in multiparous
What grip is used when delivering a baby and why?
Herrell/Finnish grip + hand on head to slow down
Reduce risk of perineal tears
What happens in the third stage of pregnancy?
Uterus contract hard and shear off placenta and expel within 10 mins of delivering baby
What is the active management of the third stage of pregnancy and why?
Routine use of uterotonic drugs
Deferred clamping and cutting of cord
Controlled cord traction after signs of separation of placenta
Decrease risk of PPH
What uterotonic drugs can be used?
Syntocinin
Syntometronin
Carboprost
Ergometrine
What is the physiological management of the third stage of pregnancy?
No routine use of uterotonic drugs
No clamping of cord until pulsation stopped
Delivery of placenta by maternal effort
When is the third stage of pregnancy considered delayed?
Active management - >30 mins
Physiological management - >60mins
What happens to the breasts during pregnancy?
Hypertrophy of ductular-lobular-alveolar system with prominent lobules forming
Alveolar cells differentiate to be able to produce milk from mid gestation
Areolar enlarge and darken
Montgomery tubercles produce sebum and pheromones
What is the purpose of sebum and pheromones?
Sebum - prevent cracking
Pheromones - Baby locate nipple
Why is there little milk secretion in pregnancy?
High progesterone:oestrogen ratio
What is the composition of breast milk?
Water - 88.1% Fat - 3.8% Protein - 0.9% Lactose - 7% Other - 0.2%
What is colostrum?
First secretion from mammary glands
Low in water, fat and sugar
High in protein, IgA,M,G and white cells
How much colostrum is produced?
40ml/day for first 3 days
What are the benefits to breastfeeding?
Baby gets less infections Bonding - oxytocin Reduced risk ovarian and breast cancer Further contract uterus Weight loss
How does milk production start post delivery?
Delivery of placenta remove large amount of progesterone
Alveoli respond to Prolactin and produce milk within 24-48hrs
How is prolactin stimulated?
Suckling
Mechanical stimulation of receptors in nipple inhibit dopamine secretion in hypothalamus. Dopamine inhibit prolactin. Suckling also increase vasoactive intestinal protein which promotes prolactin.
Why is some milk made in the first 24-48 hours?
Prolactin produced by decimal cells which aren’t inhibited by dopamine
How is milk production regulated?
Suckling at one feed promote prolactin release which produces milk ready for next feed - it is a demand based production
Describe the milk let down reflex
Oxytocin released from posterior pituitary in response to suckling
Myoepithelial cells stimulated and contract squeezing milk out of breast (Milk is ejected not sucked out)
What can stimulate/inhibit oxytocin release?
Stimulate - Cry, sight of infant, fondling, anticipation
Inhibited - Pain, embarrassment, alcohol
How does milk production stop?
If suckling stop, milk production gradually ceases
This can be due to:
Turgor induced damage to secretory cells
Low prolactin levels
What drugs should be avoided while breastfeeding?
Antibiotics - cipro, tetracycline, chloramphenicol, sulphonamides Lithium and Benzo's Aspirin Carbimazole Methotrexate Sulfonylureas Cytotoxics Amiodarone Clozapine