OSCE Mechs of Labour Flashcards
- how would you introduce yourself to Ana?
Hi ana, my name is Ayesha, and I am the student midwife. Before we begin can you please confirm your name and date of birth for me thank you. It’s lovely to meet you and congratulations.
So Ana, today my practice supervisor has asked me to explain the mechanisms of labour to you and I’m going to be demonstrating this using a pelvis and baby model as part of preparation for your labour. Is that okay?
I will just take a moment to wash my hands following the five moments of hand hygiene and the seven steps of handwashing. If my hands were visibly clean, I would only use hand santiser and if they were visibly unclean I would have to wash my hands using soap and water.
- Discuss the approach you would take to delivering antenatal education
I would take an assets-based approach. This means asking Ana what she already knows and building on this knowledge in a logical manner. I will correct any misinformation she may have and give her the opportunity to ask questions. I would also use the teach back method to ensure she has correctly understood the information that I have provided her with.I would also want to be patient and empathetic as the mechanisms of labour can be a lot to take in and may bring up new worries or questions in ana about labour pains etc.
- what is the definition of the mechanisms of labour?
The widest diameter of the presenting part of the fetus negotiating its way through the widest diameter of the pelvis.
- describe the basic anatomy of the pelvis?
First, I’m going to tell you a bit about the pelvis.
This here is your pelvis. It enables mobilisation and contains and protects the pelvic organs. It has two parts; above the brim is called the ‘false’ pelvis and this does not play a role in the process of childbirth. Below the false pelvis is the true pelvis which involves the brim, cavity and outlet. During labour the fetus has to negotiate its way through the different diameters of these parts, so we’ll talk about that further.
- beginning with the pelvic brim describe the anatomy and the diameters
To begin with, the pelvic brim is at the very top here and it is bounded by the sacrum at the back which is here which also has a sacral promontory. The sacrum is one of your vertebrae’s and it curves inwards slightly which affects the shape of the pelvic brim. The bottom of the sacrum is hinged with the coccyx which is able to move backwards to increase the diameter of the outlet and assist in labour.
The brim is ovoid in shape and opposite to the sacrum here at the front is the symphysis pubis.
The pelvic brim consists of 8 landmarks;
1 – sacral promontory
2 – sacral alla (wing like structure)
3 – sacroiliac joint
4 – illiopicteal line, not visible line
5 – illiopicteal eminence which is a rough swelling at the end of the illopicteal line
6 – upper border of the superior pubic rami
7 – upper border of the pubic arch
8 – symphysis pubis
We use these landmarks to help us determine which position the baby is lying in.
Diameters of the brim;
Anterior posterior; 11cm
Oblique; 12cm
Transverse; 13cm
- describe the pelvic cavity and the diameters?
The cavity is the inner part, it is almost circular in shape and is shorter at the front because it is boarded by the symphysis pubis and longer at the back because it is boarded by the sacrum. The cavity finishes at the coccyx. As its circular all the diameters are the same; 12cm anterior posterior, 12cm oblique and 12cm transverse. The sacrum forms the curve of carys here.
- describe the pelvic outlet and the diameters?
Moving from the cavity, we have the pelvic outlet which is the last part of the pelvis that the baby must negotiate through during labour. It is partially boarded by the ligaments which are not included in the model here. The ligaments support and give strength to the pelvis and these relax in pregnancy due to the hormone progesterone. The outlet is almost diamond in shape; it is formed by the coccyx, the lower part of the symphysis pubis and the ligaments. The diameter for the pelvic outlet is the anterior posterior 13cm, oblique 12cm and transverse 11cm.
8a. describe and demonstrate the mechanisms of labour in a logical manner?
descent -What we’ll do now is describe the mechanisms of labour to you and use the baby model here to demonstrate. The first stage of the mechanisms of labour is descent, which is the presenting part of the fetus is pushed down into the pelvic brim. This is encouraged by increased abdominal muscle tone. This means that if this is your first baby, so if you are a primigravida.
This tone along with Braxton hicks contractions in the late stages of pregnancy, fundal dominance of the uterine contractions during labour and increased frequency and strength of contractions during labour will push through the fetus and cause the baby to descent towards the pelvic brim.
For someone who is parous, so having a second or subsequent baby, this may not happen until the onset of labour.
When the widest part of the fetal head has entered the maternal pelvis, we say that the baby is engaged. This means that during your antenatal examination, if we can feel three fifths or less on your abdomen, we talk about the fetal head being engaged.
8b. flexion
The next stage in the mechanisms of labour is flexion. This happens with increased descent. Fundal dominance which is the top of your uterus exerting pressure down the fetal spine towards the occiput using fetal axis pressure the baby begins to be pushed downwards and starts to meet the resistance of the pevic floor. This causes the baby to tuck in it’s chin to its chest in order to decrease the presenting diameter of tis head which assists passage through the pelvis. Increased flexion leads to decreased presenting diameters.
8c. internal rotation
Due to the hitting against the pelvic floor, the fetus will internally rotate. It will rotate from a transverse position into an anterior position as it negotiates its way through the pelvic cavity.
8d. crowning
With continued descent, the presenting part of the fetus will become visible at the vulva as the fetus pushes forwards and backwards due to the resistance of the pelvic floor. Eventually this leads to something called crowning which is when the largest diameter of the head is passed through the vulva. It reaches a point where it will no longer travel forwards and backwards but will stay stationary. This is often spoken about as the ring of fire and your midwife will provide you with some soothing methods as to ease the pain.
8e. extension
Following on from crowning, the baby’s head is born by a process of extension. The neck will pivot on the sub-pubic arch and the baby’s head will be born with the sweeping motion of the forehead across the perineum, following the curve of carys.
8f. restitution
Extension is followed by restitution. If the baby has entered the pelvis in a right occipital anterior position then the head and neck need to realign, so they will realign towards the maternal right by turning by about an 8th of a circle.
8g. external rotation of the head and internal rotation of the shoulders
Following restitution, with a couple of strong contractions we would expect to see the external rotation of the head and as this is happening the shoulders will internally rotate. This happens because the shoulders trying to negotiate into the widest diameter of the pelvis in order to be born. The fetal head will completely turn to face the maternal thigh; if the fetus began facing the right hand side, then it will externally turn towards the right maternal thigh.
8h. lateral flexion
At this stage, your baby is nearly born. If the midwife was using a hands-on approach to assisting you with birth, she would help with the final stage of lateral flexion. The baby follows the curve of carys; the curve of the sacrum which we talked about beforehand. The midwife will either use a chin occiput grip or she would hold the side of the baby’s head and would pull downwards until the anterior shoulder is delivered and visible at the vulva. Once the anterior shoulder is visible, she’s going to use an upward motion, so the posterior shoulder slips against the perineum. At this stage the midwife will deliver your baby up onto your abdomen to commence that golden hour if you would wish.
so ana, that was the mechanisms of labour and i hope it was helpful. Do you have nay questions for me?
