Session 10 - Birth Flashcards
What occurs in the first stage of labour?
- Creation of birth canal
- Onset of labour –> full cervical dilation
What occurs in the second stage of labour?
- Expulsion of the fetus
- Can take up to 1 hr
- Head flexes, rotates, and then stretches vagina and perineum with a risk of tearing. After head is delivered, the shoulders rotate and deliver and the rest follows.
What occurs in the 3rd stage of labour?
- Expulsion of placenta
- Contraction of uterus to compress blood vessels and reduce haemorrhage
- lasts up to 15 mins
What soft tisseues need to expand to create a birth canal?
- Cervix
- Vagina
- Perineum
To what size does the birth canal expand to?
~10 cm
What is the maximum size of the birth canal and the normal diameter of the fetal head?
head - 9.5 cm
pelvic inlet - 11 cm after softening of ligaments
What is cervical ripening? What triggers it?
Cervix made of tough thick coiled collagen
ripening involves - reduction in collagen production, increase in glycosaminoglycans (dirupts matrix), and uncoiling.
Triggered - prostaglandins PG E2 and F2x.
How is myometrial contractions triggered?
triggered by pacemakers and force generated by increased intracellular calcium
What substances strengthen and suppress the myometriums contractions?
strengthens - prostaglandins, oxytocin
suppresses - progesterone
How does the uterus contract during early and late pregnancy?
Early - low amplitude every 30 mins
Late - higher amplitude, less frequent. Braxton-Hicks contractions
How is prostaglandin production controlled?
by oestrogen:progesterone ratio
Progesterone > oestrogen = low prostaglandins, throughout pregnancy
Oestrogen > progesterone = high prostanglandins, end of pregnancy
What is the ferguson reflex?
Upon application of pressure to the internal end of the cervix, oxytocin is released, which stimulates uterine contractions, which in turn increases pressure on the cervix (thereby increasing oxytocin release, etc.), until the baby is delivered.
What is brachystasis?
Uterine smooth muscle relaxes less than it contracts which shortens the body of the uterus over time and forces the baby out
What happens to fetal cortisol, oestrogen and progesterone, prostaglandins, cervix, oxytocin during labour?
- Fetal cortisol increases
- Oestrogen > progesterone
- Increased prostaglandins
- Cervix stretched
- Oxytocin released from post pit - ferguson reflex
What is the apgar score?
Score assessing condition of neonate
How is maternal blood loss limited post birth? How is this process enhanced?
- uterus contracts post birth, shearing off and expeling placenta
- uterine contractions compresses blood vessels and closes them
- Can be enhanced by giving oxytocic drug
What is the most common position that the baby lies?
longitudinally, cephalic presentation and well flexed
How can inadequate power, passahe or abnormalities of the passenger lead to failure to progress in labour?
- Inadequate power - insufficient uterine contraction
- Inadequate passage - abnormal bony pelvis, rigid perineum
- Abnormalities of passenger - fetus too big or breech presentation
How can you induce labour?
giving prostaglandins and oxytocic drugs
What instruments are used for operative delivery?
forceps or vaccuum extraction
Where is a c section made?
suprapubic or hypogastric
What are the effects of oestrogen on oxytocin receptor production in the myometrium?
increases
What effect does progesterone have on the responsiveness of the uterus to oxytocin and prostaglandin release?
reduces both
Why is progesterone necessary to avoid spontaneous abortions?
Prevents oxytocin from evokning contractions during pregnancy and positive feedback mechanism of oxytocin
What postural change could occur from ostrogen mediated softening of the ligaments in the pelvis?
lordosis
what anatomical landmark gives an estimate for 20 weeks of gestation?
mothers umbilicus
What fetal landmark is used to assess fetal head position in the birth canal?
fetal fontanelles
What spinal segments does the epidural block?
T9-S4
Define post partum hemorrhage
>500 ml blood loss after delivery
what is the most common cause of PPH?
uterine atony
