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Labour: Mechanism and Delivery Minal Patel (Academic FY1)What is labour? The physiological process where a foetus is expelled from the uterus . The onset of regular and painful contractions which are associated with cervical dilatation and descent of the presenting part. Term delivery: 40 weeks (37 to 42 weeks)Stages of labour: Onset of labour: 1- regular, painful uterine contractions 2- Bloody show (shedding of the mucous plug) 3- membrane rupture (breaking of waters) Stage 1: Cervical dilation and shortening- DESCENT Latent phase: 0-4cm Active phase: 4-10cm (full dilation) Rough estimate of timings- 0.5cm/hr for primiparous, 1cm/hr formultipsStages of labour Stage 2: Full dilation to fetus delivery Passive= no urge to push with every contraction Active: Each contraction causes an urge to push - NICE states delivery occurs within 3 hrs from active pushing in primiparous, 2hrs from active pushing in multiparous.Stages of labour Stage 3: From fetal delivery to passage of the placenta and membranes. This stage can consist of active or physiological management. Anterior fontanelle: Diamond shaped Pelvic Anatomy Posterior fontanelle: Triangle shapeKey T erminology Moulding: The extent of overlapping of fetal skull bones. Can affect the shape of the baby's head when born. This occurs to help the passage of the baby's head through the pelvisCaput Succadaneum: (Oedema)swelling of the baby’s head due to pressure from cervical dilation. It can cross the midline of the fetal head. Cephalohaematoma: Accumulation of blood between the periosteum and bone. They do not extend beyond suture lines.The pelvic outlet is narrowest in between the intraspinous diameter. This is important to know as Station: A measurement of the descent of the the ischial spines determine the station of the fetus. fetal head, assessed in relation to ischial spines. At the ischial spines equals: 0Fetal head diameter The fetal head diameter varies depending on the degree of neck flexion. This is important to know with regards to descent and delivery. A: Complete flexion C: Partial extension D: Complete extensionMechanism of labour 1: ENGAGEMENT When the largest diameter of the fetal head descends into the maternal pelvis. This can occur prior to the onset of labour. It is determined by abdominal palpation and measured in fifths. <3/5ths of head palpable on abdomen= engagement2: DESCENT The descent of the fetus into the pelvis. It is a continuous process. Encouraged by: - Fundal dominance of uterine contractions - Increased frequency and strength of contraction - Increased abdominal musculature tone Head descends in L or R occiptotransverse position3: Flexion As the fetal head descends and comes into contact with the pelvic floor, fetal neck flexion occurs. This reduces the fetal head diameter to 9.5cm.4: Internal rotation This is turning of the fetal head from the occiptotransverse position to occipto- anterior. I.e. the occiput (back of fetal head) is now closest to the pubic symphysis This occurs due to the shape of the pelvic floor. This position means the head is now within the longest diameter of the pelvic outlet (AP).5: Crowning The head will become visible at the vulva. This is where the widest part of the fetal head passes through the narrowest part of the maternal bony pelvis. 6: Extension The fetal head has now passed through the suprapubic arch and extends up.7: Restitution The fetal shoulders are now reaching the pelvic floor and will turn to align with the head 8: External rotation The fetal head will turn 45 degrees to face either the L or R medial thigh of the mother. At the same time the shoulders will rotate from the transverse position to the occipito-posterior position. After this the shoulders are delivered, and the rest of the baby soon after. Summary A: Descent B: Engagement C: Internal rotation D: Extension E: External rotation and restitution F: ExpulsionFactors affectinglabour- 3 P’s 1: Power - The force of uterine contractions - Frequency of uterine contractions 2: Passage - The bony pelvis - Cervical dilatation 3: Passenger - Diameters of the fetal head, affected by: - Attitude (degree of flexion) - Position (degree of rotation) - Size of headInstrumental deliveries • 10-13% in the UK 1: Ventouse delivery-attachment of cup to the fetal head via a vacuum - Also known as suction cups or kiwi cups - During contractions, traction is applied 2: Forceps- double bladed instruments - Bladed applied around fetal head - Gentle traction with contractionsIndications for instrumental delivery: 1- Inadequate progress 2- Maternal exhausation 3- Maternal medication conditions 4- Fetal compromise - CTG or fetal blood sample Complications: - Increased risk of tears, incontinence - Cephalohaematoma - PPH - Fetal facial bruising What it involves: Induction of labour Mechanical 1- membrane sweep The process of starting labour artificially, as it it is safer for delivery 2- artificial rupture of than for baby to remain in utero. membranes Indications: 1- Maternal factors Pharmacological 1- Vaginal prostaglandins - Postdates - Preeclampsia,GDM, Obstetric cholestasis 2- Fetal factors - FGR - IUFD Bishop score An assessment of the ‘cervical ripeness’. It determines whether induction of labour is appropriate. It is based on: Table 2– Modified Bishop Score (RCOG 2001) Cervical Feature 0 1 2 3 Dilation (cm) <1 1-2 2-4 >4 Length (cm) >4 2-4 1-2 <1 Station (relative to ischial spine-3 -2 -1/0 +1/+2 Consistency Firm Average Soft – Position Posterior Mid/anterior – –Caesaerean sections Urgency of c-sections: The delivery of a baby through a Category 1: Immediate threat to life of surgical incision in the abdomen and woman or fetus (uterine rupture, major uterus. placental abruption, cord prolapse, fetal hypoxia, persistent fetal bradycardia) Indications- may be elective or planned Category 2: Maternal or fetal compromise which is not immediately - Breech. Malpresentation life threateninh - Placental praevia Category 3: No maternal/fetal - Fetal compromise compromise but needs early birth. - Multiple pregnancy Category 4: Birth timed to suit woman or healthcare provider.Learning points • Stages of labour are characterized in to 3 main categories • The mechanism of labour is defined by the differing fetal movements which result in delivery • There are differing causes for delays during labourMCQs A- Right occipito-posterior B- Left occipito-posterior C- Right occipito-anterior D- Left occipito-anterior E- Occipito-transversMCQs Which of the following in an indication for induction oflabour? - Fetal distress - Placental praevia - Twin pregnancy - Premature rupture of membranes - Gestational diabetesMCQs What anatomical structure is fetal station in relation to? - Pubic tubercle - Pubic symphysis - Ischial spines - Ischial tuberositiesThank you! Any questions?References: • Radiopeadia • RCOG esim • NICE guidelines • Geeky medics • Passmedicine