6. Parturition Flashcards
(42 cards)
How do you calculate the Estimated Date of Delivery (EDD)?
40 weeks/280 days from the first day of the last menstrual period
How do you calculate actual fetal age?
14 days less than EDD
When is “at term” delivery?
Between 37 and 42 completed weeks
When is “pre-term” delivery?
Before 37 weeks
When is “post-term” delivery?
Beyond 42 weeks
What are the boundaries for the 3 trimesters?
First trimester: Up to 12 weeks
Second trimester: 12-27 weeks
Third trimester: 28 weeks to term
How can the estimated gestational age be calculated?
- From last menstrual period
Things to consider: Memory reliability, cycle length, hormonal contraception (either regular use or emergency) - Clinical examination
- Symptoms e.g. quickening
What features of the first trimester U/S biometry are used to estimate gestational age?
Gestation sac volume for very early gestation
Crown-rump length
What features of the second trimester U/S biometry are used to estimate gestational age?
Head circumference
Biparietal diameter
Abdominal circumference
Femur length
Late pregnancy U/S biometry is for GROWTH not …
Dating
How is the pregnant state maintained?
- Uterine quiescence
- Abdominal arrangement of the cervix (provides barrier)
- Aminion and chorion membranes are intact
Changes to uterus than maintain pregnancy?
Uterine quiescence:
- Gap junction expression down regulated
- Oxytocin receptors down regulated
- Relaxin plays a role
What anatomical arrangements of the cervix help maintain pregnancy?
Collagen fibres predominate over smooth muscle
Glycosaminoglycan ground substance
PROVIDES BARRIER
What do amnion and chorion membranes contribute to maintenance of pregnancy state?
Intact means there is a low level of prostaglandin biosynthesis
How is labour initiated?
[The trigger is unknown]
- Increased oestrogen towards end of pregnancy encourages uterine contraction
- Increased PG production
- Increased cytosol-free calcium needed for muscular contraction
Oxytocin (post-pit)- presenting part presses on pelvic floor
What is the process of cervical ripening?
Prostaglandin biosynthesis increase
Increases water content of glycosaminoglycan matrix
Myometrial activity results in “effacement” and thinning of the cervix.
Relaxin upregulates matrix metalloproteinases (Try to soften everything up and thin out membrane more)
How do uterine contractions change in the initiation of labour?
Start:
Un co-ordinated, non-painful “Braxton Hicks
Progressively…
Regular, frequent, co-ordinated and painful
What are the average times for primiparous and multiparous labours?
Primiparous (first time): Av 14hours
Multiparious: Av 8 hours
What is the first stage of labour?
** Onset of regular contractions to fully dilated cervix **
LATENT PHASE:
-Onset of painful contractions 5-10min intervals
-Cervix ripening and effacement
-Cervix slowly dilating up to 3-4cm
ACTIVE PHASE:
-From cervix 3-4cm dilated, more rapidly 0.5-1cm/hr
-Progressive increase in frequency and strength of contractions
-Cervical dilatation
-Descent of the presenting part
-(Rupture of the membranes)
What is the second stage of labour?
Fully dilated cervix –> Birth
- Cervix fully dilated 10cm
- Contractions stronger 2-5mins
- Presenting part of descends
- Urge to bear down
- “Ferguson reflex” of perineal stretching
- Delivery
What is the ferguson reflex?
The Ferguson reflex is the name given to the neuroendocrine reflex comprising the self-sustaining cycle of uterine contractions initiated by pressure at the cervix or vaginal walls. It is an example of positive feedback
What is the third stage of labour?
**Expulsion of placenta and membranes **
Seperation due to forceful uterine contraction and reduces size of placenta which reduces bleeding
Normally takes 5 mins
Can be managed via..
- Expectantly (traditional or physiological)
- Actively: Oxytocic drugs (or ergotamine) may be used to assist this process. Coupled with physically pulling on umbilical cord.
Factors influencing uterine contractions…
Prostaglandins Oxytocin Relaxin Stretch response Postive feedback
Role of prostaglandins in uterine contraction control?
Prostaglandins: PGF2-alpha and PGE2
Paracrines released from uterine decidual cells
Stimulate uterine contractions
Softe, thin and dilate the cervix
Potentiate contractions induced by oxytocin
Increase gap function numbers