Labour and Delivery Flashcards
Define Labour
What is Micarriage/ Spontaneous abortion?
What is Pre-term labour?
- Expulsion of Fetus and Placenta after 24 weeks of gestation
- “” Before 24 weeks of gestation
- Labour that occurs before week 37 of Gestation
What 3 processes happen in Stage 1 of Labour?
Regular contrations until cervix is dilated
- Creation of birth canal
- Release of structures which normally retain fetus in utero
- Enlargement and realignment of cervix
What process happens in Stage 2 of Labour?
Expulsion of fetus
What process happens in Stage 3 of Labour?
Expulsion of placenta and changes to minimise maternal blood loss
When does the uterus first become palpable?
Week 12
Reaches Umbilicus at W20, Xiphisternum at W36
What is the ‘Lie’ of the fetus?
What is the commonest ‘Lie’?
Relationship of long axis of fetus to long axis of uterus
Longitudinal, with head or buttocks posterior (Normally has a flexed attitude)
What is the ’Presentation of the fetus’?
This describes which part of fetus is adjacent to the pelvic inlet
(May be Head/ Cephalic or Breech/ Podial if lie is longitudinal)
Most commonly the baby lies longitudinally, in a Cephalic presentation, well flexed.
What is the diameter of presentation in this case?
9.5 cm
The birth canal cannot dilate beyond the limits determined by the Pelvis (True diameter is 11cm)
What are the Posterior, Lateral and Anterior boundaries of the Pelvic Inlet?
Posterior: Sacral Promontory
Lateral: Ilio-Pectineal line
Anterior: Superior Pubic Rami and upper margin of Pubic Symphysis
Softening of pelvic ligaments allows some expansion of the pelvic inlet.
What are 2 important things that must happen for a birth canal to be created?
- Cervical dilation
- Anterior retraction of cervix
(During this creation process, Fetal membranes rupture and amniotic fluid is released)
How is Cervical Dilation facilitated and produced?
- Facilitated by structural changes known as Cervical Ripening/ Softening
- Produced by forceful contractions of uterine smooth muscle, which first thin the cervix (EFFACEMENT), then dilate it
The cervix has a high CT content and is made up of collagen fibres embedded in a proteoglycan matrix.
How does Cervical Ripening/ Softening change this?
What does this lead to?
- Reduction in Collagen, Increase in GAGs-> Reduced aggregation of collagen fibres
- This leads to Collagen Bundles ‘loosening’
Other than changes to the CT content of the Cervix, what changes occur in Cervical Ripening/ Softening
- Influx of inflammatory cells
- Increased NO output
What triggers all the changes in Cervical Ripening?
Prostaglandins (namely E2 and F2-Alpha)
What 2 factors cause increased thickness of the myometrium in pregnancy?
What generates force? (Hint: it’s smooth muscle)
- Glycogen deposition
- Increased cell size (10x)
An intracellular apparatus containing actin and myosin, triggered by a rise in [Ca]i
Why can some parts of the Myometrium act as ‘Pacemakers’?
Hence the myometrium is spontaneously motile
Some Smooth Muscle Cells are capable of spontaneous depolarization and AP generation
Describe the contractions in early pregnancy and as it continues
(None are forceful enough to have an effect on the fetus)
Early;
- May occur every 30mins
- Low amplitude
As pregnancy continues;
- Frequency falls
- Increase in amplitude-> ‘Braxton-Hicks’ contractions
The onset of labour is a relatively sudden increase in frequency and amplitude of contractions.
What are 2 hormones involved in this change and how do they work?
- Prostaglandins: Enhance Ca release from intracellular stores
- Oxytocin: Lowers threshold for triggering APs
(Onset of labour is associated with increased prostaglandin synthesis and release, in conjunctival with increased oxytocin sensitivity)
As contractions increase, the Ferguson Reflex increases Oxytocin secretion. Describe this
- Sensory receptors in Cervix and Vagina are stimulated by contractions
- Excitation-> Hypothalamus by Afferents-> Oxytocin release
(This +ve feedback makes contractions more forceful and frequent)
Uterine smooth muscle has a property called Brachystasis.
Describe this
- At each contraction, muscle fibres shorten but do not relax fully
- The uterus (especially the fundus) shortens progressively, pushing the fetus downwards and stretching the cervix
(Thus, descent of the fetus occurs during labour)
Although unclear in humans, evidence from animals suggests that labour is initiated by what?
- Increased Prostaglandin production and Oxytocin sensitivity
- Triggered by a fall in Progesterone levels relative to Oestrogen
Will prostaglandins induce labour when given medically?
Yes
Explain how can labour progression affect placental blood flow.
What can this lead to?
- Increasingly forceful uterine contraction may temporarily reduce placental blood flow, reducing O2 supply to Fetus
- May lead to brief reductions in fetal heart rate
- If flow reductions are greater than usual, larger ‘dips’ may occur, and the Fetus becomes ‘Distressed’
When does the First Stage of Labour end?
How long does the Second Stage last in the Multiparous woman and in Primigravida? (Ends with delivery of fetus)
When cervical dilation reaches 10cm
Multiparous;
- Up to an hour
Primgravida;
- Up to 2 hours
