Preterm Labour Flashcards
Definition of suspected preterm labour
Women who have reported symptoms of preterm labour + clinical assessment (speculum or digital vaginal exam) confirm its possibly, but rules our established labour
Definition of established preterm labour
Progressive cervical dilatation from 4 cm with regular contractions before 37+0 weeks
Definition of preterm prelabour rupture of membranes (P-PROM)
Where a woman has ruptured membranes before 37+0 weeks but is not in established labour
* Complicates 3% of pregnancies and is associated with 30-40% of preterm births
Definitions of extreme preterm, very preterm and moderate to late preterm
Under 28 weeks: extreme preterm, 28 – 32 weeks: very preterm, 32 – 37 weeks: moderate to late preterm
Incidence of preterm labour
15 million babies are born preterm worldwide (worldwide: 4-18%, UK: 7%)
Presentation of preterm labour
- Regular or frequent sensations of abdominal tightening (contractions) and abdominal cramps
- Constant low, dull backache and a sensation of pelvic or lower abdominal pressure
- Preterm rupture of membranes- in a gush or continuous trickle of fluid after the membrane around the baby breaks
- Vaginal spotting or light bleeding
- P-PROM
- A change in type of vaginal discharge- water, mucus-like or bloody
Describe the biochemistry of labour
- Throughout pregnancy, pro-pregnancy factors such as progesterone, relaxin, hCG and pro-relaxation prostaglandins (e.g. prostacyclin) will inhibit myometrial contractility
- Onset of labour involves synchronisation of myometrial activity through greater expression of gap junctions connecting myometrial cells
- Chances in the cervix occur due to: Breakdown of collagen, changes in proteoglycan concentration, infiltration of leukocytes and macrophages, increases in water content
- Labour is associated with a global increase in a number of proinflammatory factors (prostaglandins, cytokines, chemokines)- influx of inflammatory cells into uterine tissue may result in increased levels of pro-inflammatory cytokines
- Inflammation is also therefore implicated in infection-driven preterm labour
What is the role of oxytocin and prostoglandins in labour
Oxytocin stimulates contractions and production of prostaglandins via increased expression of the oxytocin receptor during labour (rather than increased circulating oxytocin)
Prostaglandins promote cervical ripening and myocardial contractility:
* Formulations of prostaglandins are used to induce labour
* Prostaglandin inhibitors are conversely used as tocolytics
Specifics:
* The PG synthesis enzymes PGHS-2 is the rate-limiting step in PG synthesis
* The amnion is the dominant site of PG synthesis
* The myometrium is the main site of PG action
* The chorion lies in between these two and expresses the enzyme responsible for PG metabolism PGDH
* The expression of PGDH falls with the onset of labour, thus facilitating the transfer of PGs from the amnion to the myometrium
What are the causes of preterm labour
Cervical weakness: The cervix usually acts as a barrier to keep the pregnancy in the uterus and as a barrier to ascending infection (via mucus plug) since it has bactericidal properties.
* Cervical weakness is associated with painless premature cervical dilatation and a history of painless second trimester pregnancy loss
* Cervical surgery e.g LLETZ, biopsy linked to shortened cervix
* Can also predispose to infection
Infection: 20-40% of preterm partuition syndromes are related to infection. Usually, infections are ascending via bacteria that are usually found in the vagina
* May be introduced by invasive procedures
* Descending spread occurs from another primary source in the body (e.g transplacental)
* Bacteria that make up the normal vaginal flora include: gram negative lactobacilli, anaerobic bacteria and group B streptococcus, which can induce two types of infection:
* Endometritis: infection of the endometrium
* Chorioamnionitis: infection of the amniotic sac and foetal membranes- A major cause of preterm birth. Associated with foetal brain damage due to a foetal inflammatory response (high amniotic IL-6 -> intraventricular haemorrhage and periventricular leukomalacia
* 70% of P-PROMs are associated with intraamniotic infections (either pre or post)
Multiple pregnancy and uterine distension: Risk of preterm delivery rises with foetal number (most multiple births will deliver < 37 weeks) Also associated with polyhydramnios, FGR etc.
Haemorrhage: Antepartum haemorrhage, placental abruption or ischaemia may lead to spontaneous PTL. Acute bleeding leads to thrombin release which directly stimulates myometrial contraction
Stress: Maternal of foetal stress, could implicate CRH
Describe some uterine anomalies that may lead to preterm labour. What is the pathophysiology of these defects
Occur due to abnormal embryological fusion and canalisation of the Mullerian ducts- leads to abnormally formed uterine cavity
* Arcuate Uterus= minimal indentation
* Uterine didelphys= complete failure of fusion
* Septate uterus= septum runs down uterus
Risk factors for preterm labour
- Previous preterm labour or premature birth, particularly in the most recent pregnancy
- Multiple pregnancy, previous cervical surgery, uterine malformation, smoking or drug use, infection, HTN, T2DM, AI disease, polyhydramnios, increased maternal age, ethnicity, interval of less than 12 months between pregnancies
Potential complications of preterm birth
- Immediate- IVH (intraventricular haemorrhage of the newborn), NEC (Necrotising enterocolitis), retinopathy, RDS, sepsis
Long term- PTB is the leading cause of neonatal death and morbidity
* 1 in 19 preterm babies will have permanent disability
* 1 in 2 of < 26 weeks will have some sort of disability
* Impact on patient/ family
Investigations required from women reporting symptoms of P-PROM
Offer a speculum examination to look for pooling of amniotic fluid and:
If pooling of amniotic fluid is observed, do not perform any further testing (presume P-PROM)
* If not, perform an IGF-1 test or placental alpha-microglobulin-1 test of vaginal fluid (amnisure). Do not use results in isolation (look at RFs)
* IF P-PROM diagnosed test for infection using FBC, CRP, cultures etc.
* Do not perform bimanual due to risk of introducing ascending infection
What investigations are required for women reporting symptoms of preterm labour who have intact membranes
- Clinical history taking (look at antenatal notes)
- Abdominal palpation and observations
- Speculum examination (followed by a digital VE if cervical dilatation cannot be assessed- fibronectin should be taken before this)
- Foetal monitoring (CTG, USS)
- Infection screen (Urine MCS, blood culture if suggested by FBC, CRP)
- IF suspected PTL and < 29+6 weeks, advise that treatment is necessary
- IF suspected PTL and 30+0 weeks or more:
- Consider TVUSS measurement of cervical length to determine likelihood of birth within 48 hours (more than 15mm= unlikely to be in preterm labour)
Use foetal fibronectin testing to determine likelihood of birth within 48 hours for women who are 30+0 weeks or more in whom TVUSS is not accepted
* < 50ng/ml= unlikely to be in preterm labour
* Foetal fibronectin is produced at the chorionic membranes (DO NOT use in combination with TVUSS. Presence of blood, sexual intercourse, prior vaginal manoeuvres/ examination, use of lubricating gel can give false positive result)
* Produced from ~7 weeks to hold the pregnancy in place and stops being produced ~22 weeks. If detected after 22 weeks, suggests ‘glue’ is being broken down
* Very good sensitivity, poor specificity
In general what observations would trigger transfer to obstetric led care
In general, transfer to obstetric led care if: HR >120, HTN, 2+ protein, temp >38, vaginal blood loss other than show, PROM (more than 24 hours before labour), significant meconium
