85 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
What are the consequences of Pre-term birth?
- Respiratory distress
- Hypothermia
- Cerebral palsy
- Intraventricular haemorrhage
- Hypoglycaemia
- Jaundice
- Sepsis
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 ultrasound biometry are used to estimate gestational age?
- Gestation sac volume for very early gestation
* Crown-rump length
What features of the second trimester ultrasound 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
How does uterine quiescence maintain the pregnant state?
- 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 mechanical barrier
How does intact amnion and chorion membranes contribute to maintenance of pregnancy state?
Intact amnion and chorion membranes:
• Low level of prostaglandin biosynthesis
How is labour initiated?
(Trigger unknown)
- Increased oestrogen towards end of pregnancy encourages uterine contraction
- Increased PG production
- Increased cytosol-free calcium needed for muscular contraction (PG + oxytocin)
- Oxytocin (post-pit)- presenting part presses on pelvic floor
- Increased gap junction numbers at term allow coordinated contractions (PG)
- Cervical ripening
- Uterine contractions
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
How do uterine contractions change in the initiation of labour?
- Initially uncoordinated, non painful ‘Braxton Hicks’
- Progressively regular, frequent, coordinated and painful
- Upper segment (stronger contraction)/lower segment (weaker contraction)
What are the average times for primiparous and multiparous labours?
- Primiparous average 14 hours
- Multiparous average 8 hours
- 1st stage takes up most of this time and 2nd stage is about 1 hour
- 3rd stage delivery of placenta & membranes
What is the first stage of labour?
Onset of regular contractions to fully dilated cervix
- ‘Latent phase’
• Onset of painful contractions 5-10min intervals
• Cervical 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 to birth • Cervix fully dilated (10 cm) • Contractions stronger 2-5 mins • Presenting part descends • Urge to bear down • ‘Ferguson reflex’ of perineal stretching • Delivery
What is the ferguson reflex?
- Example of positive feedback and female body’s response to pressure application in the cervix or vaginal walls
- Upon application of pressure, oxytocin is released and uterine contractions are stimulated (which will in turn increase oxytocin production, and hence, increase contractions even more), until baby is delivered
What is the third stage of labour?
Expulsion of placenta and membranes
• Separation due to forceful uterine contraction and reduces size of placental bed which reduces bleeding
• Normally takes 5 mins
• Can be managed
1. Expectantly (traditional or physiological) (<60mins)
2. Actively - Oxytocic drugs (or ergotamine) may be used to assist this process (promotes contraction to reduce bleeding) coupled with physically pulling on umbilical cord (<30mins§)
What factors influence uterine contractions?
- Prostaglandins
- Oxytocin
- Relaxin
- Stretch response
- Positive feedback
Role of prostaglandins in uterine contraction control?
(PGF2α and PGE2)
- Paracrines released from uterine decidual cells
- Stimulate uterine contractions
- Soften, thin and dilate the cervix
- Potentiate contractions induced by oxytocin
- Increase gap junction numbers
Role of oxytocin (posterior pituitary hormone) in uterine contraction control?
• Triggers the phospholipase C cascade and release of intracellular Ca2+ from smooth muscle SR (OT receptors on smooth muscle cells)
• Stimulates PGF2α 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 (Ferguson reflex)
• Constricts uterine blood vessels at the site of the placenta
Role of relaxin in uterine contraction control?
• Produced by the corpus luteum, 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 of ligaments
• Pregnant women vulnerable to ligamentous strain
• Not just a pregnancy hormone (receptors in heart, smooth muscle and connective tissues)
What is the decidua?
- Uterine lining (endometrium) during a pregnancy, which forms the maternal part of the placenta
- Formed under the influence of progesterone and forms highly characteristic cells
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
- E.g. multiple gestation pregnancy, polyhydramnios
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?
- Characteristics of uterus:
• Quiescent - Physiology:
• Maintained by progesterone and relaxin
What are the characteristics of the uterus and physiology for stage 1?
- Characteristics of uterus:
• Uterine ‘awakening’
• Initiation of parturition –> complete cervical dilation - 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?
- Characteristics of uterus:
• Active labour
• Complete cervical dilation –> delivery - Physiology:
• Oxytocin release triggered by Ferguson reflex
• Prostaglandins
What are the characteristics of the uterus and physiology for stage 3?
- Characteristics of uterus:
• Delivery –> expulsion of placenta + final uterine contractions - Physiology:
• Oxytocin
What is the process of the engagement of head during delivery and labour?
- Engagement of head - ‘lightening’
- 2-4 weeks prior to delivery in primiparous women
- May not happen in multiparous women
- Presenting part descends into the pelvis
What are the different delivery presentations?
- Engagement of and flexion of the head
- Internal rotation
- Delivery by extension of the head - nose scrapes the blanket
- Delivery of the shoulders
What is the normal lie and altitude of the foetus during pregnancy?
- 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/vertex presents first (neck extended would be abnormal)
% of the different presentations (part that is delivered first)?
- ACephalic 97%
- A Breech is buttocks first 3%
- Shoulder <1%
What is external cephalic version?
• Manipulation of fetus through abdomen from breech to cephalic presentation
• Aim to reduce elective C section for breech
• Success rate about 50%
• <5% revert to breech if successful
• From 36 weeks nulliparous or 37 weeks
multiparous
• Can relax uterus with tocolysis (salbutamol
or terbutaline)
Role of tocolytics?
- Relax uterus
* e.g. salbutamol or 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 cardiotocography (CTG)
What does a partograph measure?
- Fetal HR
- Rate of cervical dilatation
- Descent of fetal head
- Contraction characteristics
- If membranes ruptured – colour of amniotic fluid
- Volume of maternal urine
- Record of medications
- Maternal vitals
