Table 1 Characteristics of included quantitative studies

1. Iams and Johnson [21], single centre, study duration 1983 to 1986 (abstract only), USA

370 high-risk women based on Creasy scoring system were selected from 2829 women attending antenatal clinic. One hundred eighty-two women received routine antenatal care plus preterm birth prevention clinic the intervention and 188 women received routine antenatal care.

Preterm birth prevention clinic group received education about symptoms and signs of labour and the cervix examined at weekly visits between 20 and 36 weeks’ gestation

Control group received standard antenatal care.

1.Preterm labour (intervention vs control):

50/182 vs 40/188, P = 0.17

2. Preterm birth < 37 weeks (intervention vs control):

24/50 (48%) vs 35/40 (87.5%), P = 0.001

No significant difference between the two groups with regards to the incidence of preterm labour.

Significant difference between the two groups with regard to preterm birth among women who developed preterm labour.

2. Main et al. [22], single centre, study duration: 3.5 years, USA

367 black women at gestational age > 18 weeks were at high risk of preterm labour based on Creasy et al. [32] scoring criteria.

Inclusion criteria: Black women with gestational age < 18 weeks were referred to the nurse specialist in the Preterm Labour Detection Clinic.

Intervention group: N = 178, maternal age (yr) 23.9 ± 5.5, gravidity 3.7 ± 1.9, parity 1.4 ± 1.2, abortions ≤ 14 weeks 1.0 ± 1.0, abortion > 14 weeks 0.3 ± 0.7, women with previous preterm delivery 38%, gestational age at first visit (wk) 12.5 ± 3.7.

Control group: N = 198, maternal age (yr) 24.1 ± 5.1, gravidity 3.8 ± 1.9, parity 1.6 ± 1.5, abortions ≤ 14 weeks 0.9 ± 1.1, abortion > 14 weeks 0.3 ± 0.7, women with previous preterm delivery 43%, gestational age at first visit (wk) 12.0 ± 3.3.

Attending a preterm labour detection clinic on a weekly or biweekly basis from 22 weeks’ gestation and cervical assessment by 1 of 3 physicians at each visit. Also education provided by a nurse specialist regarding subtle signs of labour.

High risk control: received usual prenatal care.

1.Preterm deliveries (intervention vs control):

<28 weeks: 3% vs 3.9%, p = 0.42,

32 < 34 weeks: 6.6% vs 6.2%, p = 0.51,

<36 weeks: 16.7% vs 13.4%, p = 0.46,

<37 weeks: 23.2% vs 20.7%, p = 0.32,

2. Neonatal outcomes:

5-min Apgar <5 4.5% vs 6.1%, p = 0.32.

Caesarean birth: 23.7% vs 21.2%, p = 0.64.

NICU admission: 10.4% vs 16.4%, p = 0.32.

Length of stay > 5 days: 21.4% vs 18.7%, p = 0.33.

Stillborn: 4.8% vs 2.9%, p = 0.53.

Neonatal deaths: 0% vs 0.7%, p = 0.48.

3. Cost/Hospital charges:

Maternal charges: $5687 ± 4222 vs $5846 ± 4872, p = 0.97

Neonatal charges: $4958 ± 26,491 vs $4287 ± 24,247, p = 0.83.

4. Maternal hospital admission:

Mean no. maternal hospital admissions: 1.7 ± 1.1 vs 1.3 ± 0.7, p = 0.0001,

Women with one or more antepartum admissions: 44% vs 26%, p = 0.001.

No significant differences between the two high risk groups with respect to mean gestational age at delivery, birth weight or percentage delivering before term.

3. Mueller-Heubach [23], study duration 3 years between September 1984 and August 1987, USA

5457 women were scored for risk of preterm birth using the Creasy scoring system 1980, and 18.1% were classified as high risk these were randomised into two groups.

Exclusion criteria: Patients registered after 28 weeks’ gestation.

The intervention group received weekly cervical examinations and teaching about signs and symptoms of preterm labour. Health care professionals received similar instructions.

Historical control was used due to high contamination.

The control group received the usual antenatal care.

Preterm birth rate (intervention vs control): 22.1% vs 20.8%, p > 0.05

Preterm birth in year one: 13.7%, in year two 9.3%, p < 0.001 and in year three 8.9%.

Neonatal death (second and third year):

5/1755 vs 11/1203 the incidence: 2.8/1000 vs 9.1/1000.

There was no difference in preterm birth between the intervention and the control. There was a significant reduction in preterm birth rate in year 3 compared to year 1.

There was a significant decrease in the neonatal death in the second and third year of the intervention compared with the control.

4. Goldenberg et al. [24], five centres, study duration 1982–1986 (singleton and, multiple pregnancies), USA

1000 high risk women were randomized to intervention or control. Seventy percent were black and 35% were younger than 20 years and 4% were 35 years or older. 3.5% in the intervention had multiple pregnancy and 4.2% in the control.

Inclusion criteria: women with an estimated date of delivery between 1 November, 1982 and April 1, 1986, at < 30 weeks gestational age, women were classified as high risk based on a score of 10 or more on the based on Creasy et al. [32] criteria.

The intervention group attended the clinic weekly and pelvic examination and education about preterm signs and symptoms. Primary care was provided by a specially trained nurse who saw the same woman.

Women in the control group received usual prenatal care.

1. Pregnancy outcomes (intervention vs control):

Spontaneous preterm labour: 26.9% vs 16.3%

Spontaneous premature rupture of membranes (PROM) 6.3% vs 4.4%

Preterm delivery incidence: 6.3% vs 2.5%

Spontaneous delivery < 28 weeks: 2.7% vs 1.3%, p > 0.05

Spontaneous delivery <36 weeks: 11.8% vs 10.5%, p > 0.05

Spontaneous delivery < 37 weeks: 15.9% vs 14.2%, p > 0.05

Birth weight 1500–2499 g: 37.7 ± 3.8 vs 38.1 ± 3.1, p > 0.05

Mean birth weight: 2892 ± 771 vs 2935 ± 679, p > 0.05

2. Neonatal outcomes:

Respiratory distress syndrome: 5.9% vs 3.8%, p > 0.05

Hyperbilirubinemia: 7.9% vs 9.4%, p > 0.05

Necrotizing enterocolitis: 0.6% vs 1.8%, p > 0.05

Patent ductus arteriosus: 2.4% vs 1.6%, p > 0.05

Interventricular haemorrhage: 1.8% vs0.4%, p < 0.05

Congenital anomaly: 6.75 vs 7.8%, p > 0.05

Sepsis: 0.8% vs 0.8%, p > 0.5

Hypoglycaemia:2.3% vs 4%, p > 0.5

Need for resuscitation: 8.2% vs 8%, p > 0.05

NECU: 27.4% vs 26.6%, p > 0.05

Time on ventilator: <12 h:93.5 vs 97.4, P < 0.05; >12 h: 6.5% vs 2.4%, p < 0.05

Babies days in hospital: ≤7: 89% vs 91.8%, p > 0.5; >7 11% vs 8,2%, p > 0.05

Preterm labour diagnosis and spontaneous preterm PROM diagnosis were higher in the intervention group, but the difference was not significant.

No significant difference between the groups on most the neonatal outcomes.

5. Hobel et al. [25], multicentre study, 5 clinics in the intervention and three in the control, recruitment lasted from 1983 to 1986, USA

1774 high-risk women in the intervention clinics and 880 in the control clinics. Women were predominantly Hispanics.

Inclusion criteria:

Had a gestational age of <31 week, no disabling condition, and were English or Spanish speaking.

Exclusion criteria: major congenital anomaly, multiple births, pregnancies with missing charts of cost information.

Intervention group received preterm birth prevention education plus increased antenatal visits to the clinic and selected prophylactic interventions. Visits were scheduled at 2 weeks intervals, 3 educational classes about preterm birth prevention, nutritional and psychosocial screening and offered treatment when it was needed.

The control clinics offered visits at 4 weeks intervals up to 30 weeks ‘gestation, then every 2 weeks from 30 to 35 weeks’ gestation, then weekly until delivery.

1. Number of clinic visits(intervention vs control): 6.4 ± 3.4 vs.9 ± 2.5, p < 0.05

2. Preterm rate: 7.4% vs 9.1%, p = 0.063

3. Birth weight <2500gm: 5.8% vs 6.4%, p = 0.15

4. Gestatioanl age: 39.8 ± 2.3 vs 39.9 ± 2.5, p = 0.38

4. Inpatient costs per New born:

<37 weeks: (n = 95, 17,206 ± 3995 vs n = 55, 31,129 ± 8572)

≥37 weeks: (n = 70, 2025 ± 273 vs n = 70, 2763 ± 628)

5. Average new born inpatient cost:$3146 vs $5342

No significant difference between the two groups with regards to the incidence of preterm birth, low birth weight and gestational age.

High risk prevention clinics had an average cost savings of $2196 for new born care (p = 0.2).

1. Herron et al. [26], prospective-cohort, single centre, between July 1, 1978 and June 30, 1979, USA.

Patients were screened based on the Creasy criteria 1980 and divided into two groups:

176 (15.2%) women assigned to the high risk group and 974 (84.8%) to the low-risk group.

For the high risk group:

The intervention involved: the first visit to the clinic included education regarding the signs and symptoms of preterm labour and training the participants in self-detection of painless contractions. Weekly antenatal visit to the clinic, if the symptoms of painless labour occurs then patients were monitored for 1–2 h. Reporting to the clinic immediately if one of the preterm signs and symptoms occurred. AT the weekly visit the pelvic examination was performed by the same physician. If preterm labour occurred then patients admitted to hospital and tocolytic therapy was given.

Staff training and education to prompt response to patients’ complaints, of any preterm signs and symptoms, early admission to patients having a mild increase uterine activity, aggressive therapeutic approach in patients with documented preterm labour, awareness of long term side effects of the tocolysis.

1.Preterm labour(comparing high risk group to low risk):

30/176 (17.5%) vs 24/974 (2.5%), p < 0.05,

2. Preterm delivery (comparing high risk group to low risk group):

7/176 (4%) vs 9/974 (0.9%), p > 0.05.

3. Men gestational age at delivery (comparing high to low group):

33.7 ± 2.6 vs 33.3 ± 3.6 weeks

4. Preterm birth ≤ 36 weeks at year 1 after introducing the clinic: 2.4% compared with 6.75% before the clinic.

A significant decrease in preterm birth with the clinic.

2. Manuck et al. [27], Retrospective cohort, multi-centre study from 17 hospitals, participants’ enrolment from 2008 to 2010, USA.

Inclusion criteria: Single pregnancy, previous PTB <35 weeks.

Exclusion criteria: Women who delivered preterm babies <37 weeks due to medical or foetal complications, eg, preeclampsia, foetal growth restriction.

Women excluded from the study analysis if they had a history of incompetent cervix (painless cervical dilation <24 week’s gestation).

Total number of patients: 223

PTB clinic group: n = 70

Maternal age 28.5 years, white 83.1%, smoking 3.4%, married 86.4%, primary obstetrics provider is perintalogist 18.6%; number of PTB <37 weeks 1.7 (mean)

Usual care group: n = 153

Maternal age 28.8% years, white 88.8%, smoking 9.8%, married 83%, primary obstetrics provider is perintalogist 11.8%; number of PTB <37 weeks 1.6 (mean)

The recurrent PTB prevention clinic includes three visits (10–18 weeks, 19–24 weeks, and 28–32 weeks):

Detailed obstetric history and personal recurrence risk assessment: at visit 1 (10–18 weeks)

Screen for BV and treat if positive with oral metronidazole at all three visits.

Urinalysis : at all three visits

Urine culture: at all visits (symptoms positive or urinalysis is positive).

Transvaginal cervical length: at all visits. Cervical length <2.5 cm is abnormal.

Offer 17 alpha hyroxyprogesterone caproate: at visit one for all patients, patients who declined were offered the treatment again at week 24 if cervical shortening is noted.

Usual care group:

Managed by their primary obstetrician without being referred to the clinic.

Primary outcome (PTB clinic vs usual care):

1. PTB < 37 weeks,%: 48.6% vs 63.4%, p=0.02

2. PTB < 37 weeks,%: 5.7% vs 13.7%, p=0.08

3. Delivery GA, mean wk: 36.1 vs 34.9, p = 0.02

Secondary outcomes:

1. Neonatal morbidity, %: 5.7 vs 16.3, p = 0.03

2. NICU admission, %: 44.3 vs 41.2, p = 0.66

3. Mean inpatient maternal cost: $6929 vs $7706, p = 0.48

4. Mean inpatient neonatal cost: $11,818 vs $15,662, p = 0.05

28% reduction in the risk of recurrent PTB <37 weeks and >1 week of pregnancy prolongation and reduced the rate of major neonatal morbidity with the intervention.

3. Karkhanis et al. [28], retrospective-cohort from November 2007 to January 2009, Birmingham-UK (abstract)

180 high risk women, mean age 29.85 years (18–41), mean BMI = 27.52 kg/m2, N = 158 with previous preterm labour or mid trimester loss.

All patients in the preterm prevention clinic underwent serial transvaginal scan monitoring and infection screening between 16 and 28 weeks.

40 women underwent cervical cerclage and progesterone

35 women received progesterone only

1. Term delivery > 37 weeks: n = 123/180

2. Term delivery >37 weeks after one preterm delivery (PTD): 79%

3. Term delivery > 37 weeks after 2 PTD:71%

4. Term delivery >37 weeks after 3 PTD:60%

5. NICU admission: n = 36 babies

6. Infant mortality: n = 7

The preterm prevention clinic reduced prematurity rate.

4. Burul et al. [29], retrospective-cohort, clinic cases from January 2005 to December 2008, London-UK (abstract).

210 cerclage cases: 85 cases before the establish of the clinic and 125 afterwards

Cervical cerclage

1. Elective cervical cerclage 44% before the clinic vs 88% after establishing the clinic

2. GA at delivery 28 + 2/40 before the PTBC compared with 35 + 2/40 with the clinic care

5. Cohen et al. [30], audit of two London preterm surveillance clinics between January 2013 and May 2014, UK (abstract).

509 pregnancies reviewed; mean age 33.6 years (18–49 years), BMI 24.4 (range 17–48), 59% White and 15% Afro-Caribbean.

Reasons for referral to the clinics: Previous cervical treatment (50%)

Previous preterm birth before 34 weeks 926%), mid trimester miscarriage (MTL) (17%)

Uterine anomalies (2%)

Multiple pregnancy (3%)

Clinic interventions:

Cervical shortening found in 44%

Progesterone supplementations 25%

Cervical cerclage 27%

Preterm delivery:

<28 weeks 0.7% delivered

<34 weeks 4% delivered

<37 weeks 11% derived

Early referral to the clinics for better monitoring.