Primary prevention

There are many causes and many risk factors for preterm labor and consequently there is no single preventive strategy. Protocols for monitoring asymptomatic high-risk women are not established, but prophylactic interventions may be offered to women at risk. Prior preterm birth or a short cervical length (<2 cm) and a positive fetal fibronectin test place a woman at higher risk of preterm delivery. Between one third and one half of women who have a positive fibronectin test at 23 weeks' gestation deliver before 30 weeks.[47][48]

Interventions to decrease the risk of preterm labor preconception

  • Maternal lifestyle modification through education, with an emphasis on general health improvement, smoking cessation, appropriate activity, and exercise may help, but few lifestyle interventions improve outcome.

  • Limiting the number of embryos transferred in assisted conception.[24]

  • Less-invasive techniques for treating cervical intraepithelial neoplasia (CIN) may be adopted, and vaccines against human papillomavirus (HPV) may reduce the incidence of CIN and subsequent surgical treatment.[41]

Interventions to decrease the risk of preterm labor postconception

  • Behavioral and lifestyle factors: bed rest, abstinence from sexual intercourse, and dietary manipulations (e.g., hydration, avoiding caffeine) have not been shown to improve outcome.[58][59]​​​ Initial enquiry about potentially modifiable risk factors, such as smoking, recreational drug use, domestic violence, urinary tract infections, and previous cervical procedures, is recommended. All pregnant women should receive advice and support to stop smoking. See Smoking cessation. Enhanced prenatal care is no more successful than routine care at reducing the rate of preterm birth in socially deprived populations.

  • Fetal ultrasound: can be used to accurately assess gestational age, provide an estimated weight for neonatal team, and allows for early identification of fetal anomalies that may increase the risk for, or necessitate, preterm birth.[60]

  • Antibiotic therapy: screening for abnormal vaginal flora can identify women at increased risk, particularly if bacterial vaginosis is found early in pregnancy.[14] However, treatment does not consistently improve outcome.[61] Routine screening of women for bacterial vaginosis is therefore not recommended.[15] Treatment of asymptomatic urinary bacteriuria (as well as symptomatic urinary tract infections) is thought to be beneficial.[62] After preterm prelabor rupture of membranes, there is some evidence that antibiotic therapy with either penicillin or erythromycin may be effective at reducing preterm labor.

  • Tocolytic agents: may prolong gestation by between 2 to 7 days and are recommended for short-term use to provide time for administration of prenatal corticosteroids and transfer to an appropriate neonatal unit.[63][64]​​ They are not recommended for prolonged use. See Management approach.

  • Dental caries, poor dentition, and periodontal disease: may be associated with an increased risk for preterm birth.[30] However, whether maintaining good dental hygiene throughout pregnancy can help prevent preterm delivery is not known and requires further research.[65]

Cervical cerclage or vaginal progesterone

  • Cervical cerclage involves placing a stitch around the upper part of the cervix to keep it closed. It is an established prophylactic intervention used for many years. Initial observational studies were very promising, due to high success rates, but randomized trials of this intervention have demonstrated only a marginal benefit.[66][67]​​​ In women with short cervical length (<25 mm), a previous spontaneous preterm birth, and a singleton pregnancy, cerclage is associated with a reduction in morbidity and mortality.[68] However, cerclage does not seem to reduce rates of preterm delivery in low-risk women, and the evidence for high-risk women is limited.[69]​​[70]​ Cerclage may increase the risk of cesarean section.[67]

  • The UK National Institute for Health and Care Excellence guidelines suggest offering prophylactic cervical cerclage or vaginal progesterone to women with a history of both spontaneous preterm birth or midtrimester loss, and a cervical length of 25 mm or less (based on the results of a transvaginal ultrasound between 16 and 24 weeks of pregnancy).[71]​ Prophylactic vaginal progesterone alone can be offered for either of these indications and is endorsed by the American College of Obstetricians and Gynecologists and International Federation of Gynaecology and Obstetrics (FIGO).[72][73]​​​ If progesterone is used, treatment is started between 16 and 24 weeks of pregnancy, and continued until at least 34 weeks.[71]​ Cervical cerclage can also be offered to women with a cervical length of 25 mm or less, and a history of either preterm prelabor rupture of membranes or a history of cervical trauma.[71]​

  • Cerclage and vaginal progesterone are thought to be similarly effective for women with a singleton gestation, previous spontaneous preterm birth, and a short cervix.[74]​ In one meta-analysis, both vaginal progesterone and cerclage reduced the risk of preterm birth, but the certainty of evidence for cerclage was low and only vaginal progesterone significantly improved neonatal outcomes.[70]

  • The benefit of cerclage is not dependent on the degree of shortening of the cervix.[75] Indications for cerclage placement should not be based on ultrasound criteria alone, but should include historic factors (e.g., previous preterm birth).[76] Ultrasound surveillance may be considered in high-risk women who have not received a cerclage.[77]

  • The cerclage suture can be placed higher by mobilizing the bladder, or by a transabdominal operative approach (including laparoscopically).[78]​​​[79]​​​ One randomized controlled trial (RCT) comparing the use of abdominal cerclage with vaginal cerclage demonstrated that the abdominal route was superior to both high and low vaginal cerclage, significantly reducing preterm birth prior to 32 weeks gestation and reducing fetal death.[80]

  • Cerclage has also been used as an emergency measure in an attempt to delay labor, by 1 month on average, once the cervix has dilated and membranes have been exposed to the vagina.[81][82] Most supportive evidence comes from cohort studies and RCTs are warranted, but as preterm delivery is extremely likely at this point, this intervention seems justified provided there is no clinical evidence of infection and no significant uterine activity.[79]

  • The use of cerclage in multiple pregnancies is less clear, but low-quality evidence suggests it may be beneficial for prevention of delivery prior to 34 weeks where the cervix is <15 mm.[83]​ Meta-analyses suggest vaginal progesterone is not beneficial to multiple pregnancies and may be associated with increased adverse effects.[84][85][86]

Secondary prevention

Measures will depend on the underlying etiology but may include cervical cerclage or progesterone therapy.

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