Physiology of Pregnancy and Labour Flashcards
List the cell stages a fertilised ovum goes through before implantation
Fertilised ovum
Cleavage (4-cell/8-cell stages)
Morula
Blastocyst
During which days following fertilisation does the blastocyst enter the uterus?
Days 3-5
During which days following fertilisation does the blastocyst attach to the lining of the uterus?
Days 5-8
Which surface cells help the blastocyst penetrate and adhere to the endometrium?
Trophoblastic cells
By what day following fertilisation does the blastocyst become fully buried in the endometrium?
Day 12
Which tissue is the placenta derived from?
Trophoblast and decidual tissue
How is the placental cavity formed?
Trophoblastic cells differentiate into syncitotrophoblasts which invade the decidua of the endometrium to form cavities filled with maternal blood
How does the embryo communicate with the placenta?
Placental villi containing capillaries
There is no direct contact between foetal and maternal blood. True/False?
True
By which week of pregnancy are the foetal heart and placenta fully functional?
5th week
HCG stimulates the corpus luteum to secrete what hormone?
Progesterone
Oxygen-saturated blood goes to the foetus via which vessel?
Umbilical vein
Oxygen-poor blood goes from the foetus to the mother via which vessels?
Uterine veins
What 3 factors increase the supply of O2 to a foetus?
Foetal Hb has increases carrying capacity
Higher Hb concn in foetal blood
Foetal Hb can carry more O2 in low PCO2 (Bohr effect)
Drugs can cross the placental barrier - list some teratogens
Thalidomide Carbamazepine Tetracyclines Alcohol Nicotine Heroin, cocaine
What is the effect of human chorionic somatomammotropin (HCS)?
Decreases insulin sensitivity of mother
Protein tissue formation
Breast development
What effect does progesterone have on uterine contractility?
Decreases contractility
What effect does oestrogen have on the uterus?
Increases size of uterus
Relaxation of ligaments
What happens to the cardiac output during pregnancy?
Increases to cope with demands of uteroplacental circulation
Can be up to 50% above normal around 24wks!
When does cardiac output typically decrease in pregnancy?
Last 8 weeks due to uterus compressing vena cava
What happens to Hb levels during pregnancy? What is the consequence?
Decrease due to dilution of blood
Require iron supplements
What effect does progesterone have on CO2 levels?
Stimulates brain to lower CO2 levels by increasing respiratory rate
What is pre-eclampsia?
Pregnancy-induced hypertension and proteinuria
Taking folic acid during pregnancy reduces the risk of what?
Neural tube defects
Taking vitamin B during pregnancy helps what?
Make red blood cells (erythropoeisis)
Taking vitamin K before birthing prevents what?
Intracranial bleeding during labour
Towards the end of pregnancy, how does the ratio of oestrogen:progesterone change?
Ratio increases - oestrogen promotes contractility
Which hormone secreted from the posterior pituitary helps stimulate contractions in labour?
Oxytocin
Give an example of positive feedback from the foetus that increases contractility during labour
Cervical stretch due to foetus head
N.B. also increases oxytocin release
What are the 3 stages of labour?
1: cervical dilation (8-24hrs)
2: passage through birth canal (0-30mins)
3: expulsion of placenta
Oestrogen and progesterone inhibit milk production. True/False?
True
After birth, levels drop to facilitate lactation
Which hormone stimulates lactation?
Prolactin
What 2 stimuli cause lactation in the “milk let-down” reflex?
Baby crying
Baby suckling
What should be expelled from the uterus in normal labour?
Foetus
Membranes
Umbilical cord
Placenta
What is Ferguson’s reflex in labour?
Pressure on the cervix triggers a hormonal pathway that leads to uterine contractions and dilation of cervix
Why might hydrocortisone be given to a pre-term baby?
Help mature its lungs
There are 3 stages in labour. What does stage 1 comprise of?
Latent phase: 3-4 cm cervical dilation
Active phase: 4-10 cm cervical dilation
There are 3 stages in labour. What does stage 2 comprise of?
Full cervical dilation to delivery of baby
There are 3 stages in labour. What does stage 3 comprise of?
Delivery of baby to expulsion of placenta and membranes
Describe the clinical features of the latent phase of stage 1 of labour
Mild irregular intrauterine contractions
Cervix softens and shortens
May last a few days
Describe the clinical features of the active phase of stage 1 of labour
Contractions become more rhythmic and intense
Cervix achieves full dilation
Slow descent of presenting part of baby
When is stage 2 of labour considered prolonged in a nulliparous woman?
If it exceeds 3 hours where there is analgesia
If it exceeds 2 hours where there is no analgesia
When is stage 2 of labour considered prolonged in a multiparous woman?
If it exceeds 2 hours where there is analgesia
If it exceeds 1 hour where there is no analgesia
Why are oxytocic drugs recommended for stage 3 of labour?
Help contractions
Reduce risk of post-partum haemorrhage
What chemical causes cervical softening?
Hyaluronic acid
What causes cervical ripening during labour?
Decrease in collagen fibre alignment and tensile strength
What are Braxton Hicks contractions?
Tightening of the uterine muscles to aid body to prepare for birth
Not usually felt until 2nd/3rd trimester
How long typically are the gaps between “true labour contractions”?
5 minutes
How do Braxton Hicks contractions differ from true labour contractions?
BHC: irregular, do not increase in frequency/intensity, resolve with change in activity
TLC: regular, increasing frequency/intensity, don’t resolve
What does it mean if a baby is “born in a caul”?
Born with some membrane/amniotic sac still surrounding it
Describe the “normal” presentation of a baby as it passes through the pelvic canal
Longitudinal lie, cephalic presentation
Occipito-anterior, then occipito-transverse with flexed head
What presentations are classified as “abnormal” in a baby’s birth?
Transverse/oblique/breech lie
Occipito-posterior engagement
There is a relationship between the clinical state of the cervix and the onset of labour. Which 5 parameters are assessed under the Bishops score?
Effacement Dilation Firmness Position Level of presenting part
List options for analgesia during labour
Paracetamol TENS Entonox Diamorphine Epidural anaesthesia Remifentanyl
What would be considered an abnormal amount of blood loss during labour?
More than 500ml
When does placental expulsion occur following delivery?
5-10 mins
Considered normal up to 30 mins
How long does it take tissues to return to non-pregnant state in puerperium?
6 weeks
