Recurrent Preterm Birth

Recurrent preterm birth is two or more spontaneous births before 37 weeks. It results from causes that persist between pregnancies, including cervical insufficiency, uterine anomaly, chronic infection and inflammation, and genetic and environmental factors. The recurrence risk rises with each earlier preterm birth. It matters because a cause is found in a proportion, and treatment of that cause lowers risk.

• Risk factors: very early earlier births, cervical surgery, uterine septum, smoking, low body mass index, short interval between pregnancies.
• Surgery on the cervix or uterus may cure a structural cause.
• A hospital-based plan should be in place by 20 weeks.

Women have a history of two or more preterm births, sometimes with painless dilatation, rupture of membranes or labour at a similar gestation each time. Examination between pregnancies may show a cervical defect.

• Pattern of birth at a similar gestation.
• Cervical scarring or a bicornuate or septate uterus on assessment.
• Differential diagnosis: cervical insufficiency, uterine anomaly, intrauterine infection, medically indicated preterm births, genetic predisposition.
• Complications: further preterm birth, mid-trimester loss, preterm rupture of membranes, chorioamnionitis, neonatal death or disability.

The approach is to review the earlier births, look for a structural or infective cause and monitor the cervix.

• Review each earlier birth for gestation, cause and cervical findings.
• Three dimensional ultrasound, hysterosalpingography or hysteroscopy for uterine septum or other anomaly before the next pregnancy.
• Transvaginal cervical length every 1 to 2 weeks from 14 to 24 weeks.
• Urine culture, high vaginal swab, chlamydia, gonorrhoea, syphilis and HIV tests; TSH and HbA1c.

The principle is to treat a structural cause, start progesterone and cerclage early and monitor the cervix closely.

• Supportive: preconception review; space pregnancies by at least 18 months; stop smoking; treat infection; avoid heavy lifting; early hospital review at 20 weeks and a written plan; teach warning signs.
• Pharmacological: micronised progesterone 200 mg vaginal at night from 16 weeks to 36 weeks; metronidazole 400 mg oral 12-hourly for 7 days for bacterial vaginosis; cefalexin 500 mg oral 6-hourly for 7 days for bacteriuria; azithromycin 1 g oral once for chlamydia; benzathine benzylpenicillin 2.4 million units IM once weekly for 3 weeks for syphilis; betamethasone 12 mg IM twice, 24 hours apart, between 24 weeks and 34 weeks and 6 days if labour starts; magnesium sulphate 4 g IV over 20 minutes then 1 g per hour until delivery for 24 hours at most, before 32 weeks.
• Procedures: McDonald cerclage at 12 to 14 weeks for three or more earlier preterm births or mid-trimester losses or a history of painless dilatation, and at 16 to 24 weeks for a cervical length below 25 mm, with cefazolin 2 g IV once and indomethacin 100 mg rectal once; remove at 36 to 37 weeks or at once for labour, rupture or infection; hysteroscopic resection of a uterine septum before conception; transabdominal cerclage before or in early pregnancy where a vaginal cerclage has failed or the cervix is very short.
• Special groups: women with a uterine anomaly have growth and presentation scans at 28 and 34 weeks; HIV positive women continue tenofovir 300 mg, lamivudine 300 mg and dolutegravir 50 mg oral once daily.
• Red flags: contractions, leaking fluid, bleeding, pelvic pressure, fever, cervical length below 25 mm, funnelling.
• Follow-up: cervical length every 1 to 2 weeks to 24 weeks; antenatal review every 2 weeks from 20 weeks; birth in a unit with neonatal intensive care.