8 - labour and delivery Flashcards
labour is referred to after how many weeks of pregnancy?
24 weeks
define parturition
birth before 24 weeks - it is often called spontaneous miscarriage
what is pre-term labour?
labour that occurs before the 37th week
what are the three stages of labour?
1a - creation of a birth canal
1b - release of the structures that normally keep the fetus in utero
1c - enlargement and realignment of the cervix and vagina
2 - expulsion of the fetus
3 - expulsion of the placenta and changes to minimise blood loss from the mother
what is the lie of the fetus?
the relationship of the long axis of the fetus to the long axis of the uterus (longitudinal/ transverse)
what is the presentation of the fetus?
describes which part of the fetus is adjacent to the pelvic inlet
if laying longitudinally presenting part will be head (cepahlic) or breech (podalic)
what is the pelvic inlet bounded by posteriorly, laterally and anteriorly ?
posterior: sacral promontory
lateral: ilio-pectineal line
anterior: superior pubic rami and pubic symphysis
what retains the fetus in the uterus?
the cervix and inactivity of the myometrium
outline the processes in creating a birth canal
stage 1
1) - softening of the pelvic ligaments
- cervix must dilate and retract anteriorly
- fetal membranes rupture releasing amniotic fluid
- cervical dilatation facilitated by cervical ripening
what is cervical softening (ripening)
stage 1
- reduction in collagen
- increase in glycosaminoglycans GAGs
- decrease the aggregation of collagen fibres
- collagen bundles loosen
- influx of inflammatory cells
- influx of nitric oxide
- changes triggered by prostaglandins (E2 F2a)
describe the properties of uterine smooth muscle which facilitate labour
stage 1
- myometrium is made of smooth muscle - gets thicker over pregnancy
- actin and myosin apparatus (triggered by i[Ca] generates a force
- rise in calcium is produced by APs in the cell membrane
- APs spread from cell to cell creating co-ordinated contractions
- some smooth muscle cells can depolarise spontaneously
- myometrium is therefore always spontaneously motile
- contractions in early pregnancy and then increases in amplitude later on, although frequency decreases, BRAXTON HICKS contractions produced
- increase in frequency and force of contractions = onset of labour
2) BRACHYSTASIS
at each contraction the muscle fibres shorten but do not relax fully.
uterus fundal region shortens progressively
this pushes the presenting part into the birth canal and stretches the cervix over it
what 2 hormones are involved in the onset of labour and what do they do?
stage 1
PROSTAGLANDINS:
enhance the release of calcium from intracellular stores
labour - stimulates more forceful contractions
OXYTOCIN: peptide hormones PP lowers the threshold for triggering APs labour - increased sensitivity to oxytocin
as contractions increase what reflex increases oxytocin secretion massively?
stage 1
FERGUSON REFLEX
positive feedback stimulated by the cervix and vagina stimulates hypothalamus via afferent nerves to release oxytocin
what are the normal physiological processes which initiate labour?
stage 1
increase in prostaglandin production
increase in oxytocin sensitivity
fall in progesterone levels relative to oestrogen
what is the end of the first stage of labour? (cervical dilatation)
10cm
