10 Flashcards
When do pregnancies end?
With the expulsion of the products of conception (i.e. fetus and placenta)
What is labour?
- process where fetus, placenta and membranes are expelled through birth canal
- when the expulsion of products occurs after 24 weeks of gestation
- normal labour is spontaneous in onset at term (37-42 weeks)
See physiological labour slide 7-8
If expulsion of placenta and fetus occurs before 24 weeks of gestation, what is it called?
- spontaneous abortion (miscarriage)
- parturition
See physiological labour slide 2
What is the term for labour that occurs before the 37th week of gestation?
-premature or pre-term labour
What environment is the most conducive to a normal physiological birth?
- calm, private, oxygenated
- little need for sterility
- need high levels for oxytocin for birth process and for feeding baby
- birth process is a continuum from in-utero to ex-utero for baby
- no break in concentration
See physiological labour slide 3
What are the main processes during the first stage of labour?
- creation of a birth canal
- release of the structures which normally retain the fetus in utero
- enlargement and realignment of the cervix and vagina
What is the main process during the second stage of labour?
-expulsion of the fetus
What is the main process of the third stage of labour?
-expulsion of the placenta and changes to minimize blood loss from the mother
Describe the uterine muscle fibres
- longitudinal muscles: push baby out
- circular muscles: around Fallopian tubes and cervical end for dilation
- oblique muscles that go across the uterus and contracts to cut blood supply of placenta
See physiological labour slide 4-5
What occurs during the first stage of labour?
The fetus, placental membranes and uterus increase dramatically in size during gestation. The uterus first becomes palpable at around 12 weeks of gestation, by 20 weeks it has reached the level of the umbilicus, by 36 Pregnancies end with the expulsion of the products of conception; i.e. weeks it reaches the xiphisternum.
See physiological labour slide 9-10
What is the “lie” of the fetus?
- describes the relationship of the long axis of the fetus to the long axis of the uterus
- commonest lie is longitudinal, with the head/buttocks posterior
- fetus normally has a flexed attitude
What is the “presentation” of the fetus?
- describes which part of fetus is adjacent to the pelvic inlet
- if baby lies longitudinally the presenting part may be the head or the breech
Describe what occurs during pre-labour
- lightening occurs 2-3 weeks prior to to the onset of labour
- expansion of the lower segment
- fetal head engages
- symphysis pubic widens, sarcomere-iliac joints relax
- pelvic floor relaxes
- increased vaginal secretions
- frequency of micturition
- Braxton hicks contractions
- taking up of the cervix
See physiological labour slide 11-12
In what position does the baby usually lie in the fetus?
- commonly lies longitudinally in cephalon presentation
- well flexed so that the vertex presents to the pelvic inlet
- birth canal needs to have a diameter of about 10cm for fetus to pass through
How is the birth canal dilated through cervical softening?
-The cervix has a high connective tissue content made up of collagen fibres embedded in a proteoglycan matrix.
-Ripening involves a marked reduction in collagen and marked increase in glycosaminoglycans (GAGs), which decrease the aggregation of collagen fibres. In consequence collagen bundles ‘loosen’.
-There is also influx of inflammatory cells, and increase in nitric oxide output. All of these
changes are triggered by prostaglandins, namely E2 and F2a
How does the uterine smooth muscle help in dilation of birth canal?
- The myometrium is made up of bundles of smooth muscle cells.
- During pregnancy, the myometrium gets much thicker due primarily to increased cell size (10 fold) and glycogen deposition.
- An intracellular apparatus containing actin and myosin, triggered by a rise in intracellular calcium concentration, generates force.
- The rise in calcium concentration is produced by action potentials in the cell membrane.
- Action potentials spread from cell to cell via specialised gap functions, allowing co-ordinated contractions to spread over the myometrium.
- Some smooth muscle cells are capable of spontaneous depolarization and action potential generation, and so can act as ‘pacemakers’.
- The myometrium is therefore always spontaneously motile. In early pregnancy contractions may occur every 30 minutes or so, but are of low amplitude.
- As pregnancy continues, the frequency falls, with some increase in amplitude, producing noticeable ‘Braxton-Hicks’ contractions. -None of these contractions are normally forceful enough to have any effect on the fetus.
See physiological labour slide 14
What are the two main hormones implicating the sudden increase and force of contractions during labour?
- prostaglandins: enhances the release of calcium from intracellular stores
- oxytocin: secreted from posterior pituitary under the control of neurons in the hypothalamus; acts by lowering the threshold for triggering action potentials
See physiological labour slide 15-23