Threatened preterm birth without rupture of membranes

  • Overview/procedure description

    When faced with possible labour prior to 34 weeks gestation, the principal aim is to effectively suppress labour with tocolytic therapy (unless contra-indicated) for at least 48 hours to enable administration of steroids to accelerate fetal lung maturity, and if not at a site equipped to safely delivery prior to 34w, if possible arrange safe in utero transfer.  There is no evidence of benefit from prolonged use of tocolytic therapy.

    Related Policy

    Nil

    Definition of Terms

    PIPER     Paediatric Infant Perinatal Emergency Retrieval

    Procedure details

    1.       Confirm the diagnosis

    2.       Defer delivery for at least 48 hours (to enable steroids to take effect) and if possible until >34 weeks gestation

    3.       If not at a site equipped to safely deliver prior to 34 weeks, if possible arrange safe in utero transfer

    4.       If in utero transfer not feasible due to the progress of labour, facilitate support/retrieval by PIPER Neonatal.

    Confirming the diagnosis

    The mother has made a presumptive self-diagnosis when she presents reporting the onset of contractions. Note that 50% of these women will actually still deliver at term.

    The diagnosis is confirmed if, after a period of observation, regular painful contractions are observed, AND these have resulted in progressive effacement and/or dilatation of the cervix. But even in the presence of an effaced and partly dilated cervix, a substantial proportion of these women will still go on to deliver at term.

    However the diagnosis may be presumed if, on speculum examination and performance of a fetal fibronectin test, the test result is positive. Although ‘false positive’ results may occur after coitus, intercourse or digital vaginal examination, a fFN test should still be performed, as its principal value lies in its negative predictive value—while only 30% of women with a positive fFN will birth within 7 days, 98+% of women with a negative fFN will not birth within the next 7 days. The combination of a positive fFN and a cervical length <15mm increases the positive prediction of delivery occurring, as does a history of previous preterm birth.

    Admission and Initial Assessment

    History                            –   note especially previous preterm births, known multiple pregnancy, known prior cervical surgery and/or shortening of cervix of prior ultrasound cervical surveillance, cervical cerclage in place.

    Observations                  –   vital signs, noting particular maternal fever.

    Abdominal examination –    uterine tone and tenderness, fetal size and presentation, adequacy of liquor.

    Sterile speculum examination in the absence of ruptured membranes or bleeding, if the cervix is closed proceed to a fFN test, and take the opportunity to perform a low vaginal swab (for GBS, trichomonas, mycoplasma).  If the cervix is dilated and forewaters visible, try to avoid digital vaginal examination if possible and consider placing the patient semi-prone with a pillow under her hips, to take pressure off the forewaters. Ultrasound may be helpful in confirming presentation and estimating fetal weight.

    Fetal well-being should be evaluated by CTG.

    An MSU should also be sent, and consideration given to uPCR screening for chlamydia/gonorrhea/ureaplasma.

    Initial treatment

       
    1. Administration of corticosteroids

    Betamethasone 11.4mg IM, repeated in 24 hours

    Although this may make glycaemic control more difficult in women with diabetes, this can usually be accommodated by adding or increasing insulin short-term.

       
    1. Tocolysis

    Nifedipine (not Nifedipine SR) 20mg orally chewed and taken with orange juice, repeated in 20 mins and again 20 minutes after that, then maintain on 20mg three times a day x 48 hours.

    Nifedipine may cause flushing, headaches, tachycardia and uncommonly, hypotension and left ventricular failure. IV access should be established and baseline bloods (FBE, U&Es, LFTs) taken.

    The onset of action is usually within 30-60 minutes, and second-line therapy should not be considered within the first 2 hours.

    Nifedipine is contraindicated in the presence of pre-existing hypotension, left ventricular failure, cardiac conduction defects, and concurrently with magnesium sulphate infusion as profound hypotension may result.

    The recommended maximum daily dose is 120mg.

    GTN patch 5-10mg may be used as an alternative, or a second-line therapy if contractions persist for 2 hours after commencing nifedipine.

    GTN also causes headache, flushing, tachycardia and hypotension, the onset of peak action is 1-2 hours after administration, and it is NOT recommended for routine first-line use. However it is part of the standard drug supplies available to an ambulance crew, so may be used as an alternative when patients are being transferred directly to hospital from home.

    A repeat dose may be administered after 1 hour if necessary, up to a maximum dose of 20mg in 24 hours.

    IV salbutomol infusion is not commonly used now, as it may lead to severe maternal tachycardia and hypotension, pulmonary oedema and cardiac failure. One ampoule of salbutomol, 5mg in 5 mL, is added to 100 mL saline, the infusion commenced at 12 mL/hr and increased every 30 minutes by 4 mL/hr to a maximum infusion rate of 36 mL/hr.

    It should not be used concurrently with nifedipine, as the side-effects tend to be additive. It may also cause significant hyperglycaemia in diabetic patients.

       
    1. Antibiotics administration

    If labour is progressing and GBS status is unknown, prophylactic antibiotics may be administered IV according to local protocols.

    Call PIPER on 1300 137 650

    Unless already at a site with appropriate neonatal facilities to manage a potential preterm birth at the gestation presenting, in utero transfer is usually required.

    A midwife escort is NOT usually required, as the skill set of the paramedics are sufficient to provide safe care in most cases, and delivery in transit is not anticipated.

    In most cases, you will be asked to reassess cervical dilatation before the patient leaves by ambulance, and if there has been further cervical dilatation despite tocolysis, call back the PIPER Perinatal consultant immediately, as in utero transfer may no longer be a safe option.

    While extremely preterm infants are significantly advantaged by being born in a tertiary centre after a successful in utero transfer, delivery in transit is to be avoided as it will seriously compromise the infant.  The PIPER Perinatal on-call consultants are all senior clinicians, and will be assisted in determining the safety of a particular transfer by receiving timely and accurate information from referring clinicians, as well as input from the duty PIPER Neonatal consultant. If transfer is not considered feasible, PIPER Neonatal will provide neonatal support and retrieval.

    Use of magnesium sulphate as prophylaxis against cerebral palsy

    While there is evidence that pre-birth administration of magnesium sulphate reduces the incidence of cerebral palsy in surviving extremely premature infants, it is NOT recommended that this be administered prior to in utero transfer.

       
    • The concurrent use of nifedipine and magnesium sulphate may result in profound maternal hypotension. 
    • Safe continuation of the magnesium sulphate infusion can be problematic during ambulance transfer, and  
    • In many cases, after tocolysis birth may not occur for days/weeks.

    After discussion with the Directors of the three tertiary maternity services, it has been agreed that use of magnesium sulphate will be deferred until the patient has arrived at the tertiary centre and been assessed there.

    The exception could be in those cases where in utero transfer has been deemed inappropriate due to labour progressing, and birth is intended to occur at the peripheral maternity unit, where it MAY be feasible to administer magnesium sulphate. But note that in most cases, nifedipine tocolysis will be continuing, in order to slow labour and increase the likelihood of the PIPER Neonatal retrieval team arriving before or very soon after birth, so magnesium sulphate will remain relatively contra-indicated. Please discuss on a case-by-case basis with the PIPER Perinatal consultant.

    Reference

    • Honest H, Bachmann LM, Gupta JK, Kleijnen J, Khan KS. Accuracy of cervicovaginal fetal fibronectin test in predicting risk of spontaneous preterm birth: systematic review. BMJ. 2002; 325(7359): 289-290. 
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    • Watson DL, Kim SJ, Humphrey MD. Study of cervicovaginal fetal fibronectin status to guide treatment of threatened preterm labour. Aust N Z J Obstet Gynaecol. 1998; 38: 185-187
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    • King JF, Flenady VJ, Papatsonis DNM, Dekker GA, Carbonne B. Calcium channel blockers for inhibiting preterm labour (Cochrane Review). In: The Cochrane Library, Issue 1 2003. Oxford: Update Software.
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    • K Duckitt, S Thornton. Nitric oxide donors for the treatment of preterm labour (Cochrane Review). In: The Cochrane Library, Issue 1, 2003. Oxford: Update Software.
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