6. Parturition Flashcards
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
Role of oxytocin (posterior pituitary hormone) in uterine contraction control?
Trigger the phospholipase C cascade and release of intracellular Ca2+ from smooth muscle
Also..
- Stimulates PGF2alpha production
- Fetal oxytocin (moving to maternal circulation) involved in the onset of labour
- Maternal oxytocin is released in bursts as a consequence of dilation of the cervix (in the Ferguson reflex)
- Constricts uterine blood vessels at the site of the placenta
Role of relaxin in uterine contraction control?
- Produced by the CL, placenta and decidua
- Contributes to uterine quiescence during pregnancy
- Release increases immediately before labour
- Softens and helps cervix dilate during labour
- Affects collagen metabolism, softening the ligaments
- Pregnant women vulnerable to ligamentous strain
- Receptors also in heart, smooth muscle and connective tissue
What is the decidua?
Thick layer of uterus mucus membrane during pregnancy
Role of mechanical stretch in uterine contraction control?
Increase in uterine contents to critical level may stimulate uterine contractions via a uterine smooth muscle stretch reflex
Role of positive feedback in uterine contraction control?
- Uterine contractions stimulate prostaglandin release which increases the intensity of uterine contractions
- Uterine contractions stretch the cervix which stimulates oxytocin release (Ferguson reflex) and stimulates further uterine contractions
What are the characteristics of the uterus and physiology for stage 0?
Characteristic of the uterus: Quiescent
Physiology: Maintained by progesterone and relaxin
What are the characteristics of the uterus and physiology for stage 1?
Characteristic of the uterus: Uterine “awakening”, initiation of parturition, extending to complete cervical dilatation
Physiology: Increase in gap junction connectivity (prostaglandins), increase in oxytocin receptor numbers (oestrogen)
What are the characteristics of the uterus and physiology for stage 2?
Characteristic of the uterus: Active labour, from complete cervical dilatation to delivery
Physiology: Oxytocin release triggered by the Ferguson reflex, prostaglandins
What are the characteristics of the uterus and physiology for stage 3?
Characteristics of the uterus: From delivery to expulsion of the placenta and final uterine contractions
Physiology: Oxytocin
What is the process of the engagement during delivery and labour?
2-4 weeks prior to delivery in primiparous women
May not happen in multiparous women
Presenting part descends into the pelvis
Stages:
- Engagement of and flexion of the head
- Internal rotation
- Delivery be extension of the head
- Delivery of the shoulders
What are the different delivery presentations?
– Cephalic 97%
– Breech is buttocks first 3%
– Shoulder 1%
Presentation i.e. part that is delivered first
what is the normal lie and altitude of the foetus during pregnancy?
(longitudinal axis) Lie: 99.5% are longitudinal – spines of mother and baby are parallel (transverse would be abnormal more common in preterm and multiple pregnancies)
Attitude: baby normally lies in the ‘fetal’ position – head tucked into the chest - crown of head/verte presents first (neck extended would be abnormal)
What is external cephalic version?
Manipulation of fetus through abdomen from breech to cephalic presentation
Aims to reduce elective C section for breech
Success rate is about 50%
From 36 weeks for the nulliparous or 37 weeks multiparous
Can relax uterus with tocolysis
Role of tocolytics?
Suppress premature birth
e.g. Salbutamol and terbutaline
During intrapartum monitoring, what are you watching in the mother and foetus?
Maternal:
- Vital signs, increasing in frequency as labour progresses
- Progress (partograph)
Fetal:
- Auscultation of the fetal heart rate and pattern
- Inspection of the liquor once membranes are ruptured
How is Auscultation of the fetal heart rate and pattern performed?
Intermittent with pinard stethoscope or hand held Doppler
Continuous electronic monitoring with cardiotocogrpahy (CTG)
What does a parograph measure?
- FetalHR
- Rate of cervical dilatation
- Descentoffetalhead
- Contractioncharacteristics
- If membranes ruptured, what is the colour of amniotic fluid
- Volume of maternal urine
- Record of medications
- Maternal vitals
Consequences of pre-term birth
Respiratory distress Hypothermia Cerebral palsy: Intraventricular haemorrhage Hypoglycaemia Jaundice: Due to immature B/B barrier Sepsis
