Flashcards in Repro Session 10 Deck (61):
Term given to expulsion of products of conception before 24 wks of gestation?
what is premature/pre-term labour?
labour (expulsion of conception products after 24 wks of gestation) occurring before 37th wk of gestation
3 processes expulsion of fetus requires? (3 stages of labour)
creation of birth canal- release of structures which normally retain fetus in utero, and enlargement and realignment of cervix and vagina
expulsion of fetus
expulsion of placenta and changes to minimise blood loss from mother
when does uterus 1st become palpable?
around 12 wks of gestation
when does uterus reach level of umbilicus?
by 20 wks gestation
when does uterus reach xiphisternum?
by 36 wks gestation
boundaries of pelvic inlet?
poster: sacral promontory
laterl: ilio-pectinal line
anter: superior pubic rami and upper margin of PS
commonest lie of fetus?
how is cervical dilatation produced?
forceful contractions of uterine smooth muscle- 1st thin cervix and then dilate it
describe cervical ripening which facilitates cervical dilatation
marked reduction in collagen and increase in GAGs which decreases aggregation of collagen fibres. Keratin sulfate (GAG) increases at expense of dermaton sulfate, so collagen bundles loosen. Also inflammatory cell influx and increase in NO output.
All changes triggered by PGs-E2 and F2x
which 2 hormones cause sudden increase in frequency and force of uterine contractions at labour onset, and how do they work?
PGs and oxytocin
PGs: enhance release of Ca2+ from IC stores
Oxytocin: lowers threshold for triggering APs
how is PG synthesis increased in endometrium?
fall in progesterone or rise in oestrogen, which alters release of phospholipase from liposomes
PG release may also be stimulated by oxytocin
how are uterine smooth muscle cells made more sensitive to oxytocin?
by fall in progesterone levels relative to oestrogen which increases the receptor pop.
how does +ve feedback occur to make uterine contractions more forceful and frequent?
sensory receptors in cervix and vagina are stimulated by contractions, and excitation passes via afferent nerves to hypothalamus to promote massive oxytocin release
what is brachystasis?
property of uterine smooth muscle that means at each contraction, muscle fibres shorten but do not relax fully, so uterus, partic. fundal part, shortens progressively, which pushes presenting part into birth canal and stretches cervix over it
how is progress in labour plotted?
graphically on a partogram
what occurs in the first stage of labour?
creation of birth canal- max size determined by pelvis
what determines max size of birth canal?
pelvis- size of pelvic inlet may be increased by softening of ligaments
normal size of pelvic inlet?
typical diameter of presentaion?
2 requirements for birth canal formation?
structural changes: will enable expansion to take place, =cervical ripening
lot of force: uterine smooth muscle contractions will actually produce birth canal through dilatation of cervix
uterine smooth muscle contractions cause what before dilating the cervix?
effacement= thinning of cervix
PGs causing cervical ripening= structural changes where cervix softened in order to allow dilatation mediated by contractions to form birth canal?
E2 and F2x
what is the Ferguson reflex?
+ve feedback mechanism in which strong uterine contractions mediates increased oxytocin secretion which further stimulates smooth muscle contraction. Contractions stimulate sensory receptors in cervix and vagina, afferent nerves transmit excitation back to hypothalamus, and this promotes massive oxytocin release causing more frequent and forceful myometrial contractions
how can separation of the placenta during the third stage of labour be aided?
administering oxytocin- induces more forceful and frequent myometrial contractions
how is the presentation diameter of the fetus reduced as it reaches the pelvic floor?
which soft tissues must expand to form the birth canal?
to about 10cm
problem of inducing labour too early?
not sufficient cervical ripening so applied force from myometrial contractions can damage cervix significantly, as cervix won't stretch in normal way
3 processes in cervical ripening?
reduced collagen as turnover favours loss
increase in GAGs
aggregation of collagen fibres reduced so less tightly associ. as matrix reduced by action of enzymes
importance of cervix being tough, thick and collagenous prior to labour?
retains fetus, prevents it from dropping down during pregnancy
how are myometrial contractions in labour induced spontaneously?
by pacemaker cells= myometrium
how are myometrial contractions suppressed prior to labour?
by progesterone- oestrogen to progesterone ratio increases for labour to occur
why must the second stage of labour occur quickly?
fetus becomes separated from placenta but is not yet able to breathe as not yet out in air where cold and physical trauma mediate baby to take first breath- lungs fill with air- massive decrease in pulmonary resistance (lose hypoxic pulm vasoconstriction?), DA closes and FO closes instantaneously as pressure increases closes flap like valve, and increase pO2 causes smooth muscle contraction in DA.
how is force generated to expel fetus
smooth muscle contraction in myometrium due to burst of APs
why do APs only have to be generated in 1 place of uterus?
cells connected to 1 another so APs spread across all cells
where are pacemaker cells of uterus located?
smooth muscle cells of myometrium in fundus and body of uterus
how could temporary interruptions in placental blood flow during forceful uterine contractions be detected?
reductions in fetal heart rate which can be measured, if flow reductions are greater than usual, larger 'dips' occur as the fetus become 'distressed'.
what does the 'lie' of the fetus mean?
relationship to long axis of uterus
fetus normally flexed
what is the 'presentation' of a fetus?
which part is adjacent to the pelvic inlet= entrance to pelvic cavity, bordered by pubic symphysis, coccyx, inferior pubic and ischial rami and sacrotuberous ligaments.
normally head 'cephalic'
sometimes buttock (podalic)- breech presentation
most common position of fetus towards end of pregnancy?
vertex to pelvic inlet at min. diameter
timings of early uterine contractions?
low amplitude- every 30 min
what are braxton-hicks contractions?
less frequent, higher amplitude contractions of late preganancy
painful but don't progress to labour
which cells does oxytocin part. act upon?
pacemaker cells of myometrium of fundus and body of uterus
where are PGs mainly produced?
what mediates increased PG levels in late pregnancy?
high oestrogen to progesterone ratio
what mediates the continuation of oxytocin release in late pregnancy?
where does oxytocin act?
smooth muscle receptors- more receptors if high oestrogen to progesterone ratio
why is brachystasis important for labour?
ensures birth canal created as fetus would never be delivered if the smooth muscles cells had to contract all the way back again each time the muscle relaxed but instead, relaxation is less than contraction so fibres progressively shorten in body of uterus to drive presenting part to cervix which gets wider and thinner
urge in second stage of labour?
to 'bear down'
delivery process of fetus in second stage of labour?
head rotates internally
head stretches vagina and perineum
head rotates and extends so that shoulder can be delivered
followed rapidly by rest
describe the 3rd stage of labour
effect of uterine contractions dramatically increased by fetus expulsion
uterus contracts down hard under continued oxytocin secretion, and b.vessles compressed to limit haemorrhage- oxytocic drug enhances this
shears off placenta
and expels its
normally within 10 mins
why does pressure in LA increase after birth?
low resistance pulmonary circulation established with increased blood flow through lungs meaning increased blood flow to left atrium via pulmonary vein so LA pressure increases, closing flap like valve of septum primum against foramen ovale of septum secundum where septum failed to meet endocardial cushions
3 elements of labour?
in what terms can uterine contractions be assessed?
frequency, amplitude and duration
create force necessary for birth canal formation and expulsion of fetus
POWER of labour
how can fetal HR be assessed during labour?
using a fetal scalp electrode
how can caesarean section facilitate fetal delivery?
o Linea alba and anterior layers of the rectus sheaths are transected and resected superiorly,
o Rectus muscles are retracted laterally or divided through their tendinous parts allowing reattachment without muscle fibre injury.
2 types of operative delivery for fetus?
vacuum extraction- ventouse
how is the condition of the neonate scored?
Apgar score: no from 0 to 10 soon after delivery and a few mins later
describe an apgar score of 0
white, flaccid tone, impalpable pulse, absent resp and repsonse
describe an apgar score of 1
blue, rigid tone, <100bmp pulse, irregular resp, poor response