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
Prevention of preterm labour
Offer a choice of prophylactic vaginal progesterone or prophylactic cervical cerclage to women with:
* A history of spontaneous preterm birth (up to 34+0 weeks) or loss (from 16+0 weeks)
AND
* Results from a TVUSS carried out between 16+0 and 24+0 weeks of pregnancy that show a cervical length of 25mm or less
(Can also consider prophylactic vaginal progesterone only where a women has one or the other)
* When using vaginal progesterone, start treatment between 16+0 and 24+0 weeks and continue until at least 30+0 weeks
* Can be given as a gel or pessary
* Decreases activity of the myometrium and prevents cervical remodelling
* Can also consider prophylactic cervical cerclage where a woman has suspicious TVUSS + history of cervical trauma or previous P-PROM
Emergency ‘rescue’ cervical cerclage:
* DO NOT offer to women with signs of infection, active vaginal bleeding or uterine contractions
* Appropriate in women between 16+0 and 27+6 weeks with a dilated cervix and exposed, unruptured foetal membranes (benefits are likely to be greater at early gestation)
* Should be done under advice of consultant and needs a plan in place to remove suture
* 50-70% ‘take home baby’ rate
Management of preterm labour
- If < 29 weeks DO NOT INVESTIGATE, continue with management straight away: tocolysis, corticosteroids, magnesium sulphate
Tocolysis:
* Nifedipine, a CCB is the medication of choice, however, Atosiban can be used as an alternative where nifedipine is contraindicated (oxytocin receptor antagonist)
* Consider nifedipine for women between 24+0 and 33+6 weeks of pregnancy who have intact membranes and are in suspected PTL (buy time)
* Rarely used (should be short term- 48 hrs for transfer of care etc)
Antenatal corticosteroids:
* Used for lung maturation (e.g. IM betamethasone)- 2 doses 12-24hrs apart, has maximal benefit if delivery is within 7 days. Can be used from ~23-34 weeks to reduce RDS
IV magnesium sulphate:
* Used for neuroprotection, since it reduces the risk of cerebral palsy
* Mothers close monitoring for magnesium toxicity at least four hourly. This involve close monitoring of observations, tendon reflexes (will cause reduced RR, BP and reflexes)
* ANTIDOTE= 10ml 10% calcium gluconate over 10 minutes
* Used for women between 24+0 and 29+6 weeks of pregnancy who are in established preterm labour OR having a planned preterm birth within 24 hours. (CAN CONSIDER between 30 and 33+6 weeks or even before 24 weeks)
* Give a 4 g IV bolus of magnesium sulfate over 15 minutes, followed by an infusion of 1 g per hour until the birth or for 24 hours
Consider intrapartum antibiotics e.g benzylpenecillin
Foetal monitoring: CTG or intermittent auscultation
What is the preferred mode of birth in preterm delivery
Mode of birth:
* There are no known benefits or harms for the baby from caesarean birth, but the evidence is very limited
* There is an increased risk of needing a vertical uterine (classical) incision (contraindicates VBAC)
* Consider caesarean birth for women presenting in suspected, diagnosed or established preterm labour between 26+0 and 36+6 weeks of pregnancy with breech presentation
* Wait at least 60 seconds before clamping the cord of preterm babies unless there are specific indications against delay
Management of preterm birth with significant meconium staining, pyrexia or known GBS
- > 34 weeks: Expedite delivery immediately (Abx if known GBS/pyrexia)
- Post-natal: observe the baby for 12 hours
Management of P-PROM
- As prophylaxis for intrauterine infection, offer women with P-PROM oral erythromycin 250mg QDS for a maximum of 10 days or until the woman is in established labour
- Can consider oral penicillin if contraindicated
- DO NOT offer co-amoxiclav
- Intense clinical surveillance for signs of chorioamnionitis and pre-term labour (may be inpatient or outpatient but at imperial- admit until 28 weeks, after which 2-3 x/week outpatient monitoring until delivery)
- Offer maternal corticosteroids (to accelerate foetal lung maturation)- 1 st line = IM betamethasone 24mg in 2 divided doses 12 hours apart
- Offer IV magnesium sulphate (for neuroprotection of the neonate) if birth is expected within the next 24 hours.
- Do not administer tocolytics (due to increased risk of infection)
- Induction of labour may be offered from 34 weeks (need to expedite delivery if non-reassuring foetal testing, infection, GBS)
- Should induce at 37 weeks
Complications of P-PROM
- Maternal: umbilical cord prolapse, placental abruption, risk of retained placenta and PPH, chorioamnionitis, oligohydramnios in early pregnancy
- Neonate: prematurity, sepsis, pulmonary hypoplasia
Definition of prelabour rupture of membranes (PROM) and prolonged rupture of membranes
Rupture of membranes which occurs at least one hour before the onset of contractions, after 37 weeks gestation.
Prolonged rupture of membranes: rupture that occurs more than 24 hours before the onset of labour
* Occurs in 10% of pregnancies
Presentation of PROM
A gush of clear fluid followed by uncontrollable intermittent trickle
Factors associated with PROM
- Associated with smoking, APH, trauma, UTI, previous PROM, uterine abnormalities, cervical incompetence, smoking, multiple pregnancy, polyhydramnios
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Pre-existing Maternal Disease60
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Cardiac Disease in Pregnancy15
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VTE and PE24
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Preterm Labour28
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Shoulder Dystocia13
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Breech Presentation24
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Induction of Labour18
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Vaginal Birth after C-section7
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Umbilical Cord Prolapse12
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Uterine Rupture8
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Perineal Tears10
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Postpartum Haemorrhage19
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Gestational Hypertension and PET30
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Gestational Diabetes19
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Anaemia11
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Obstetric Cholestasis and Acute Fatty Liver of Pregnancy23
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Foetal Growth Restriction and Large for Dates26
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Abnormalities in placentation29
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Placental Abruption8
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Amniotic Fluid Embolism7
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Rhesus Disease8
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Urinary Tract Infection14
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Syphilis, Toxoplasmosis and CMV36
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Chickenpox, Parvovirus B19, Listeria Monocytogenes35
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HSV, Rubella, GBS35
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HIV, Hepatitis29
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Labour0
