Labour and Its problems Flashcards
What are the aims of uterine contractions and what is the main difference between labour contractions and braxton hicks contractions?
The goals of uterine contractions are to dilate the cervix and to push the foetus through the birth canal. Braxton Hicks contraction do not cause the cervix to dilate whilst labour contractions do.
What affect does progesterone, oestrogen, oxytocin, the foetus itself and stretching of uterus and cervix have on myomterium excitability.
Uterine musculature becomes progressively more excitable. Oestrogen/progesterone ratio changes increases excitability. Progesterone inhibits contraction by reducing the excitability of the muscle. Oestrogen increases gap junctional communication between smooth muscle cells - increasing contractility. Oxytocin (maternal posterior pituitary gland) increases excitability. Mechanically stretching uterine smooth muscle increases contractility. Cervical stretching elicits uterine contractions. Foetal effects releasing hormones that stimulate glucocorticoids to be released from the placenta inhibiting progesterone and foetal oxytocin is also produced.
Describe the important role of prostaglandins in pregnancy and labour and what produces them.
Powerful contractors of smooth muscle and are also involved in cervical softening. Increase in oestrogen: progesterone ratio and mechanical damage stimulates prostaglandin synthesis. Placenta, decidua, myometrium and membranes can all synthesis prostaglandins. Increased synthesis of prostaglandins by amnion in third trimester. Levels of prostaglandins in amniotic fluid rise very early in labour. Cervical ripening is due to oestrogen, relaxin and prostaglandins breaking down the connective tissue.
What is the importance of oxytocin and how does the bodies reaction to it change over time?
Initiates uterine contractions, actions inhibited in pregnancy by progesterone, relaxin and low number of oxytocin receptors. Pregnancy = increased number of gap junctions to aid communication between muscle cells (coordinates effective uterine activity). At 36 weeks = increased number of oxytocin receptors in myometrium - therefore uterus can respond to pulsatile release of oxytocin from posterior pituitary gland.
What is special about myometrium?
The myometrium has special properties. Normally muscles contract and relax. Myometrial fibres contract but only partially relax. Myometrial muscle does not return to its original size so there is permanent partial shortening of the muscle fibres. This is called contraction and retraction. The uterine capacity is progressively reduced so the pressure inside uterus becomes stronger and stronger.
Describe how the contractions of the uterus spread?
Symmetry and polarity: the contractions create from two poles of uterus, then go to the fundus and upper part of the uterus, then go down to the lower segment, the forces of the upper segment are more powerful than that of lower segment of uterus.
How does the cervix change towards the end of pregnancy and in labour?
Increasing levels of relaxin during pregnancy causes changes in cervix as enzymes degrade collagen. This occurs over a period of weeks, evident from 36/40. During labour cervix offers less resistance to presenting part this is known as effacement and dilatation.
What is important to take into account about the passenger?
Size of the passenger, number of passengers (because you’re more likely to have an abnormal presentation) and position of the passenger – presentation and lie.
What is particularly dangerous about the foetus being transverse lie?
Transverse lie – umbilical cord may prolapse first and this may cause them to spasm and cause ischemia to the foetus.
What way does the foetus face when it emerges from the vagina?
Rotation of the head from a horizontal facing to looking down position as it engages with the pelvis.
Describe the two phases in the first stage of labour
Interval between the onset of labour and full cervical dilation. Two phases: Latent phase – onset of labour with slow cervical dilation to ~4 cm and variable duration. Active phase – faster rate of cervical change, 1- 1.2 cm /hour, regular uterine contractions.
What happens to the size of the uterus when the baby is born?
Marked reduction in size of uterus due to powerful contraction and retraction (ongoing). Size of placental site therefore reduced (can be up to ½ before separation begins). Inelastic placenta is squeezed by contraction.
What happens to the vasculature of the placenta before is becomes separated?
Blood in intervillous space forced back into veins of spongy layer of decidual basilis. Veins become tense and congested and kept under pressure by underlying muscle layer of uterus. Blood can’t drain back into maternal bloodstream because uterus has retracted and doesn’t allow it.
Describe a C section
Incision is suprapubic through the skin and then through the uterus. One person pushing on the fundus of the uterus acting as contractions.
How can we assist mechanically a vaginal passage of the baby?
Forceps and vacuum extraction are also used when the baby is in the wrong position.
