Threatened Preterm Labour

Threatened preterm labour is regular uterine contractions (4 in 20 minutes or 8 in 60 minutes) before 37 weeks, with intact membranes and a cervix less than 3 cm dilated. Many cases settle without treatment, and a minority progress to preterm birth. The task is to identify the women who will deliver within 7 days so that steroids, magnesium sulphate and transfer to a unit with neonatal care are given in time.

• Risk factors: previous preterm birth, urinary or genital infection, short cervix, twin pregnancy, polyhydramnios, bleeding, smoking, HIV, anaemia, malaria.
• A cervical length of 30 mm or more makes birth within 7 days very unlikely.
• Many women admitted with threatened labour deliver at term.

Women have tightening or cramping lower abdominal pain, backache, pelvic pressure, increased watery or mucoid discharge or a bloody show. Examination shows a firm contracting uterus and a cervix that is closed or less than 3 cm dilated.

• Contractions that are regular and painful rather than irregular and painless.
• Fever, uterine tenderness or foul discharge suggest infection.
• Differential diagnosis: Braxton Hicks contractions, urinary tract infection, pyelonephritis, placental abruption, chorioamnionitis, appendicitis, early labour with membrane rupture.
• Complications: progression to preterm birth, respiratory distress syndrome, intraventricular haemorrhage, necrotising enterocolitis, neonatal sepsis, neonatal death, adverse effects of unnecessary tocolysis.

The approach is to confirm contractions, examine the cervix without digital examination where possible and measure cervical length.

• Cardiotocography with tocography for contraction frequency and fetal wellbeing.
• Sterile speculum examination for membrane rupture, bleeding, dilatation and discharge; avoid digital examination until rupture and previa are excluded.
• Transvaginal ultrasound for cervical length: below 15 mm high risk, 15 to 30 mm intermediate, above 30 mm low risk; fetal fibronectin (positive at 50 ng/mL or more) or placental alpha microglobulin 1 test in the intermediate group where available.
• Urine dipstick and culture, high vaginal swab, rectovaginal swab for group B streptococcus, full blood count, C-reactive protein, malaria test, blood pressure and urine protein; ultrasound for presentation, growth and liquor.

The principle is to distinguish true from false labour quickly, give steroids and magnesium sulphate when birth within 7 days is likely, and treat infection.

• Supportive: admit women with a cervix 3 cm or more dilated, a cervical length below 15 mm or an intermediate length with a positive fibronectin; oral fluids 2 litres daily; left lateral rest without strict bed rest; avoid repeated vaginal examinations; transfer to a unit with neonatal intensive care when below 34 weeks.
• Pharmacological: betamethasone 12 mg IM twice, 24 hours apart, between 24 weeks and 34 weeks and 6 days (or dexamethasone 6 mg IM 12-hourly for 4 doses where betamethasone is unavailable); magnesium sulphate 4 g IV over 20 minutes then 1 g per hour until delivery for 24 hours at most, before 32 weeks when birth is expected within 24 hours (stop for absent patellar reflexes, respiratory rate below 12 per minute or urine below 30 mL per hour, and give calcium gluconate 1 g IV over 10 minutes for toxicity); nifedipine 20 mg oral once then 10 to 20 mg oral every 6 to 8 hours for up to 48 hours (maximum 120 mg daily) to allow steroids and transfer; cefalexin 500 mg oral 6-hourly for 7 days for bacteriuria; metronidazole 400 mg oral 12-hourly for 7 days for bacterial vaginosis; benzylpenicillin 5 million units IV then 2.5 million units 4-hourly until delivery if labour progresses and group B streptococcus status is positive or unknown.
• Procedures: none.
• Special groups: stop tocolysis and deliver for preeclampsia, abruption, chorioamnionitis or fetal compromise; twin pregnancy uses nifedipine with restricted fluids and avoids beta agonists because of pulmonary oedema; diabetes needs insulin increased by 25 to 40 percent for 72 hours after steroids; RhD negative women with bleeding give anti-D immunoglobulin 500 IU IM within 72 hours.
• Red flags: cervix 4 cm or more dilated, membrane rupture, bleeding, fever above 38 degrees Celsius, fetal tachycardia above 160 beats per minute, maternal breathlessness on nifedipine, abnormal cardiotocography.
• Follow-up: reassess contractions and cervix at 48 to 72 hours; discharge when contractions have settled and cervical length is 30 mm or more; review weekly for 2 weeks; cervical length every 2 weeks to 28 weeks.