This is a trial comparing the efficacy of oral ritodrine in the form of sustained release capsules for the maintenance of uterine quiescence after successfully treated episode of threatened preterm labor.

We randomized 120 women with singleton pregnancy who were successfully treated for threatened preterm labor before 34 completed weeks to receive either maintenance tocolysis with two 40 mg ritodrine sustained release capsules three times a day (study group, n=62) or no treatment (control group, n=58) for three days. The primary outcome measure was the recurrent episode of threatened preterm labor within 72 hours, which was defined as regular palpable uterine contractions and change in cervical effacement and/or cervical dilatation on clinical examination. Secondary outcome measures included the incidence of preterm birth, neonatal adverse outcomes, and maternal side effects.

Inclusion Criteria:

• Pregnancy between completed 24 to 24 weeks
• Successfully treated episode of threatened preterm labour by intravenous preparations
• No uterine contractions

Exclusion Criteria:

• Uterine contractions (painful, clinically palpable, or present on cardiotocography)
• Cervical dilatation of ≥5 cm
• Clinical and laboratory signs of infection defined as offensive vaginal discharge on clinical examination, vaginal pH ≥5, white blood cell (WBC) count >16×109/L, and C-reactive protein (CRP) >10 mg/L
• Positive findings of microorganisms rather than normal vaginal flora on high vaginal swab
• Any signs of fetal distress according to cardiotocography, Doppler assessment of blood flow in umbilical artery, and biophysical profile of <8.