Lecture 18: Labour and preterm birth Flashcards
What is parturition?
The process of giving birth
What defines preterm;
Less than 37 weeks of gestation
Define term;
37-40 weeks of gestation
Define post term;
41-42 weeks of gestation
Describe the correct/best orientation of baby or birth;
Placenta not blocking the cervix
Spine facing anteriorly
Head inferiorly
What is the feotus surrounded by?
Two membranes that rupture prior to birth
What are some potentially bad foetal orientation?
Spine against spine = increased risk of tearing face first (not crown of head) = larger SA
Breech
Transverse
What are the types of breech presentation?
Complete breech (butt + feet) Extended breech ( Butt , but feet by head) - most common Footling breech (feet first)
What does footling breech result in?
High chance of hip dislocation upon delivery
What are the two major physiological changes required for birth?
- Co-ordinated contractions of the uterine myometrium
- Cervical softening and compliance to allow passage of the feotus
How can labour be devided?
Into three stages
What is the first stage of labour;
Can be divided into;
- Latent phase
- Active phase
Describe the latent phase of labours first stage;
- Slow cervical dilation to 3cm.
- 30-60s contractions
- 5-20min apart
- Can last more than 24hrs
Describe the active phase of labours first stage;
More rapid cervical dilation to 10cm (fully dilated)
More than 5 strong contractions every 10 minutes
>60 seconds in duration
Describe the first and second stages in labour;
Second stage; Delivery of the fetus
Third Stage; Delivery of the placenta
What is happening in the first stage of labour?
Myometrial contractions raise intrauterine pressure, resulting in two actions;
- push the baby down
- Pull the cervix open
Cervical effacement ; thinning of the cervix
Cervical dilation; Opening of the cervix
Describe the normal cervix;
~3.5cm
- Composed predominantly of connective tissue (collagen) + (10-15%) Smooth muscle
Changes little during menstrual cycle, only during cervical ripening
What is cervical ripening?
Cervix softens and becomes more distensible
When does cervical ripening occur?
This begins prior to the onset of labour/contractions and is necessary for subsequent cervical dilation
What does cervical ripening result from?
ECM changes
Describe the ECM changes in cervical ripening;
- Hyaluronic acid content increases in the cervix , in turn increasing the water content in collagen
- Decreased dermatan sulphate reduces bridging between collagen fibres
- Increased decorin leads to collagen fibre separation
- Increased activity of the matrix metalloproteinases 2 and 9 that degrade ECM proteins.
What do the changes of cervical ECM result in?
These changes combine to decrease collagen cross linking and allow collagen fibres in the cervix to re-align in the direction of stress to allow cervical effacement and dilation when contraction begins.
What regulating factors increase in cervical ripening?
Cervical ripening results in 100 fold increase in:
- IL 6, IL 8
- Granulocyte Colony Stimulating Factor (GCSF)
What do these increased regulating factors result in?
These cytokines recruit and activate neutrophils and macrophages which secrete MMPs (metalloproteinsases)
Inflammatory cytokines also stimulate prostaglandin production which promotes cervical compliance.
What is unique about the change in uterus size?
There is no cell proliferation, just myometrial stretch
What happens during pregnancy that allows myometrium to stretch?
During pregnancy, hormones produced by the placenta suppress myometrial contractility, allowing the myometrial fibres to stretch
What are the hormones that help the uterus stretch?
Progesterone
hCG
Corticotrophin-releasing hormone
Describe the action of progesterone on the myometrium in pregnancy;
Suppresses production of prostaglandins that stimulate myocyte depolarisation, acts to reduce gap junctions that allow myometrial coupling
Describe the action of hCG on the myometrium in pregnancy;
Decreases the myosin-actin cross bridge cycling that underlies muscle contraction
Describe the action of corticotrophin releasing hormone on the myometrium in pregnancy;
Increases exponentially through pregnancy and promotes relaxation of myometrial myocytes through cAMP dependant pathways
What are two major hormones of labour onset?
CRH
cortisol
estrogen
Oxytocin
Describe cortisol function in the beginning of pregnancy;
The onset of labour is associated with increasing cortisol in fetal circulation which promotes fetal lung maturation
Describe CRH function in the beginning of pregnancy;
In humans, placental production of CRH is linked tot he onset of labour, this stimulates fetal pituitary ACTH production and fetal cortisol synthesis, potentially linking the onset of labor fetal lung maturation.
What changes to induce contractions;
Processes occur at the end of pregnancy increases;
- Maternal and fetal production of progesterone (increases precipitating labour) (only decline after the delivery of the placenta)
Rather;
- Estrogen action may increase to override the actions of progesterone
Describe the types of estrogen in pregnancy;
Estriol and estradiol present at the same concentration in pregnancy form heterodimers and negate activity.
Late in pregnancy estriol becomes dominant in concentration and forms estriol heterodimers that allows the environment to become estrogenic.
How does estrogen contribute to the onset of labour?
Estrogen;progesterone ratio increases, overriding the progesterone break by increasing production of arachidonic acid, and hence prostaglandin synthesis.
Estrogen: Progesterone ratio is key in inducing labour
What causes oxytocin production?
Tactile stimulation of the cervix+myometrium causes oxytocin release
What is the function of oxytocin?
Acts on steroid hormones, prostaglandins and NO to promote cervical softening and myometrial contractions
Describe the synchronisation of contractions in pregnancy;
Patches of myometrium contract simultaneously like a syncytium
Like a soccer crowd not entire uterus thus it generates the intrauterine pressure.
What is the second stage of labour;
- Pushing stage
- Begins when the cervix is 10cm dilated, ends with the birth of the baby
- Generally lasts less than an hour.
How can fetal heart monitoring occur?
External; Surface of mothers belly
Internal; Sensor on babies scalp (bones not fused so HB can be detected)
Describe normal fetal hear rates;
110-160 is normal BMP, increasing during contractions and rapidly returning to normal after
<110 = bradycardic >160 = Tachycardic
Low HR = forceps and emergency C-section
What is the third stage of labour?
Waiting for the placenta to deliver and physiological management of the patient.
What may be given to induce placental delivery?
“Active management”- Injection of an ecbolic/uterotonic drug into the mothers leg as the babies shoulders are delivered.
What may indicate the need for labour induction?
- Waters have broken but the onset of labour is delayed
- Gestational diabtetes
- Overdue
- Fetal concerns
- Bleeding
- High maternal blood pressure
How may labour be induced?
1) Vaginal prostaglandin administration
2) Syntocinon (mimics oxytocin effects) may be given by IV once labour has started to help contractions become strong and regular
What is extreme prematurity associated with?
Mortality and morbidity are high
What can preterm birth causes be divided into?
- Latrogenic (indicated) due to maternal-fetal complications
- Spontaneous, patients present with contractions or preterm ruptured membranes
What causes preterm labour?
Spontaneous labour seems to be the common end point of different clinical manifestations and mechanisms;
- Infection
- Stress
- Placental abruption
- Mechanical pressure
What is a common cause of preterm?
Infection and microbe invasion resulting in choriomanionitis.
Results in inflammatory cascade response in the fetal membranes
Whats another cause of preterm?
Placental abruption
What is placental abruption associated with?
Haemorrhage in the decidua basalis and localised placental infarction
Inflammation as immune system and coagulation systems are linked.
Is preterm genetic?
Potentially a group of genes may cause preterm
Treatments of preterm;
Progesterone (increases break, prior to 21 weeks for high risk women) Tocolytic meds (delays delivery up to 7 days) Prenatal corticosteroids (matures lungs) Antibiotics (improves outcomes in women with ruptured membranes)
