Previous Spontaneous Preterm Birth

Previous spontaneous preterm birth is a birth before 37 weeks that followed spontaneous labour or preterm rupture of membranes in an earlier pregnancy. It carries a raised recurrence risk, higher after two. The earlier the first birth, the higher the risk. It matters because progesterone, cervical length surveillance and cerclage can lower the risk.

• Risk factors: short cervix, genital infection, uterine anomaly, smoking, short interval between pregnancies, low body mass index, cervical surgery.
• Preconception care lowers the risk.
• Care is planned from the first visit.

Women are well, with a history of an earlier preterm labour, preterm rupture of membranes or painless mid-trimester dilatation. The current examination is usually normal.

• Gestation at the earlier birth guides risk.
• History of painless dilatation suggests cervical insufficiency.
• Differential diagnosis: cervical insufficiency, uterine anomaly, infection related preterm labour, medically indicated preterm birth (a separate risk), preeclampsia related preterm birth.
• Complications: recurrent preterm birth, preterm rupture of membranes, mid-trimester loss, chorioamnionitis, neonatal death.

The approach is to review the earlier birth and to screen for risk factors.

• Review of the earlier records: gestation, labour or rupture, cause, cervical examination, any cerclage.
• Transvaginal cervical length every 2 weeks from 16 to 24 weeks; early scan for dating.
• Urine culture, high vaginal swab for bacterial vaginosis, chlamydia, gonorrhoea, syphilis and HIV tests.
• Uterine anomaly assessment by three dimensional ultrasound or hysterosalpingography before the next pregnancy if not done.

The principle is progesterone from the mid-trimester, cervical surveillance and cerclage when the cervix shortens.

• Supportive: space pregnancies by at least 18 months; stop smoking; adequate nutrition; treat infection; avoid heavy lifting; teach warning signs; early referral to a unit with neonatal care.
• 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; folic acid 400 micrograms oral daily.
• Procedures: McDonald cerclage at 16 to 24 weeks for a cervical length below 25 mm, or at 12 to 14 weeks for three or more earlier preterm births or mid-trimester losses or a history of painless dilatation, 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 the next pregnancy.
• Special groups: earlier preterm rupture of membranes needs early recognition of leakage and antibiotics; 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.
• Follow-up: cervical length every 2 weeks to 24 weeks; antenatal review every 2 weeks from 20 weeks; birth plan in a unit with neonatal care.