Evaluation of a two-tier preterm birth prevention service in a tertiary hospital in the United Kingdom: a retrospective cohort study

Abstract

Background: Preterm birth is the most important cause of neonatal morbidity and mortality. Clinical guidelines recommend assessment of risk of preterm birth and implementation of interventions to reduce preterm birth risk through dedicated preterm birth clinics. We hypothesized that a two-tier preterm birth clinic pathway can safely manage women at the highest risk of preterm birth while reducing intervention for women at moderate risk of preterm birth. We aimed to test this hypothesis by evaluating risk factors, management, and outcomes of women attending a two-tier preterm birth prevention service.

Methods: We conducted a retrospective cohort study of women who gave birth between January and June 2021 at a tertiary hospital in Oxford, UK. We included two cohorts: women attending a Cervical Screening Clinic and women attending a Preterm Birth Clinic, and we also reviewed all cases of births before 34 weeks over that time period. At the initial midwife appointment at 8-10 weeks' gestation, risk factors for preterm birth were assessed. Pregnant women with moderate risk factors (previous preterm birth at 32^{+ 0} - 33^{+ 6} weeks, previous preterm prelabour rupture of membranes (PPROM) at 32^{+ 0} - 33^{+ 6} weeks, previous LLETZ / cone biopsy, known abnormal uterus, previous caesarean section at 10 cm dilatation, and multiple pregnancy) were referred to the Cervical Screening Clinic for a cervical length scan by a sonographer. Pregnant women with major risk factors (previous preterm birth at 16^{+ 0} - 31^{+ 6} weeks, previous PPROM at less than 32^{+ 0} weeks, radical trachelectomy, previous cervical cerclage) as well as those with a cervix < 25 mm at any scan were referred to the Preterm Birth Clinic for a cervical length scan and counselling by a specialist obstetrician. Detailed information on risk factors, management, and perinatal outcomes were collected from case notes and analysed.

Results: 189 women attended the Cervical Screening Clinic: 79.1% had a moderate risk factor for preterm birth, 100% had a cervical length scan, 7% had a short cervix and 4.2% received an intervention. All 196 infants were live born, with overall preterm birth rates of 14.8% at < 37 weeks, 3.1% at < 32 weeks, and 0% at < 28 weeks. The spontaneous live preterm birth rates were 9.7% at < 37 weeks, 2.6% at < 32 weeks and 0% at < 28 weeks. 79 women attended the Preterm Birth Clinic: 87.3% had a major risk factor for preterm birth, 100% had ≥ 1 cervical length scan, 41.3% had a short cervix, 78.1% received vaginal progesterone, and 39% had a cervical cerclage. Overall preterm birth rates were 33.8% at < 37 weeks, 10.3% at < 32 weeks and 4.4% at < 28 weeks. Spontaneous live preterm birth rates were 22.1% at < 37 weeks, 7.4% at < 32 weeks, and 2.9% at < 28 weeks. 115 women gave birth to 130 babies before 34 weeks: 80% had no major risk factor for preterm birth, 29% had a cervical length scan and less than 15% had an intervention. Over 90% had a live birth, but the neonatal death rate was high (8.5%).

Conclusion: Women with moderate risk factors for preterm birth seen in the Cervical Screening Clinic had low rates of intervention and good perinatal outcomes. Most women with major risk factors were appropriately referred and managed by the Preterm Birth Clinic. This two-tier preterm birth prevention service therefore appears safe and effective.

Keywords: Cervical cerclage; Cervical length; Preterm birth; Progesterone; Risk factor; Ultrasound.

Fig. 1

Risk factors for preterm birth. Percentage of women from the different cohorts having major risk factors (A), moderate risk factors (B) or a combination of risk factors (C). Risk factors are not mutually exclusive. The major risk factor of a short cervix (< 25 mm) refers to the time of the first clinic visit for women who attended the Preterm Birth Clinic or the Screening Clinic. Asterix (*) indicates a significant difference between the Preterm Birth Clinic and Screening Clinic with p < 0.01. Abbreviations: 32/40 = 32 weeks’ gestation, CS = caesarean section, LLETZ = Large Loop Excision of the Transformation Zone, PPROM = preterm prelabour rupture of membranes, Prev = previous, PTB = preterm birth

Fig. 2

Interventions to reduce preterm birth risk. Interventions to reduce the risk of preterm birth across the three cohorts. The interventions listed (vaginal progesterone, cervical cerclage, and Arabin pessary) are not mutually exclusive. Asterix (*) indicates a significant difference between the Preterm Birth Clinic and Screening Clinic with p < 0.01