Prevention of Preterm Labour

Article No. 8

Prevention of Preterm Labour

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The management of preterm labour involves identification of high‐risk women, prevention and treatment.  The aim is to prevent preterm labour in women at high risk or to delay delivery in a woman who has already presented with preterm labour, allowing the clinicians time to administer corticosteroids for lung maturity and antibiotics if preterm labour is associated with rupture of membranes, thereby improving the neonatal outcome.

IDENTIFICATION OF WOMEN AT RISK

Identification of women at high risk of preterm labour poses a major challenge. However the ability to identify women at risk for preterm birth has improved significantly over the past few years. This is due to the introduction of a number of predictive tests as follows.

Risk Factor Scoring. A number of risk factors for preterm birth have been identified which can be divided as modifiable and non-modifiable. Several scoring systems have been developed based on these historic/epidemiologic risk factors and daily habits in an attempt to predict women at risk for preterm birth. The single greatest risk factor for preterm birth is a history of a prior unexplained spontaneous preterm delivery.1

Sonographic Cervical Length Measurement

A strong inverse correlation exists between residual cervical length as measured by transvaginal ultrasound and preterm birth. The detection of a short cervix by transvaginal ultrasound at 18 to 24 weeks gestation is the most powerful predictor of spontaneous preterm birth.2 (Figure 1)

 

Figure1: The detection of a short cervix by transvaginal ultrasound at 18 to 24 weeks gestation is the
most powerful predictor of spontaneous preterm birth.5

 

Other specific tests and monitoring modalities

Salivary Estriol, bacterial vaginosis testing, home uterine activity monitoring (HUAM) and Fetal fibronectin measurement have been proposed to assess a woman’s risk of preterm delivery. Salivary Estriol, bacterial vaginosis testing and HUAM in recent studies have shown to have no benefit in predicting PTL The only test that is currently FDA approved and recommended by The American College of Obstetricians and Gynecologists (ACOG) for this indication is the measurement of fetal fibronectin (fFN) in cervicovaginal secretions. Elevated levels of cervicovaginal fFN (defined as > 50 ng/mL) at 22-0/7 through 34-6/7 weeks of gestation are associated with an increased risk of preterm birth. The primary value of this test lies in its negative predictive value (99% of patients with a negative fFN test will not deliver within 7 days), which may prevent unnecessary hospitalization and medical intervention.

Ultrasonographic cervical length assessment and fetal fibronectin appear to be similar in predictive ability, and the combination of both in a high-risk population maybe of value. However, further research is needed in this area. 3

PREVENTION OF PRETERM LABOUR

1.Progesterone supplement

The most important single advance of the past decade has been the introduction of progesterone supplementation for the prevention of premature labor. In 2011, the US Food and Drug Administration (FDA) for the first time has approved the use of progesterone supplementation (hydroxyprogesterone caproate) during pregnancy to reduce the risk of recurrent preterm birth in women with a history of at least one prior spontaneous preterm delivery1. Preventive treatment with progesterone can lower the rate of preterm birth in high-risk groups by more than 30% . The optimal progesterone formulation, route of delivery, and dose for the prevention of preterm birth has not yet been determined1.It is now recommended that all pregnant women who have either a prior history indicating increased risk or current, asymptomatic cervical insufficiency should receive progesterone supplementation until 34 completed weeks of gestation.

Recommendations for progesterone supplement

1. Progesterone Supplementation in Women with a History of Spontaneous Preterm Birth: There is increasing evidence that progesterone supplementation can reduce the rate of spontaneous preterm birth in this group of women 1. A woman with a singleton gestation and a prior spontaneous preterm singleton birth should be offered progesterone supplementation starting at 16-24 weeks of gestation, regardless of transvaginal ultrasound cervical length, to reduce the risk of recurrent spontaneous preterm birth.4
2. Progesterone Supplementation in Women with Cervical Shortening: Vaginal progesterone is recommended as a management option to reduce the risk of preterm birth in asymptomatic women with a singleton gestation without a prior preterm birth with an incidentally identified very short cervical length less than or equal to 20mm before or at 24 weeks of gestation4
3. Women with a Cerclage: It is not clear whether progesterone provides additional   benefit to women with a cervical cerclage in place.1
4. To treat women in preterm labor: There is no difference in the overall rate of preterm birth, admissions for recurrent preterm labor, or admissions to the neonatal intensive care unit when supplemented with progesterone.
5. Multiple Gestation: Progesterone supplementation does not prolong gestation or improve perinatal outcome in women with multiple gestations as the mechanism leading to preterm labor and delivery in multiples is different from that in singletons therefore, is not recommended as an intervention to prevent preterm birth in women with multiple gestations4 (FIGURE 2)

 

Figure 2: Adaptation from the ACOG Practice Bulletin on Prediction and Prevention of Preterm Birth in 2012 (confirmed in 2014)

 

2. Role of cervical encerclage

It has been suggested that cerclage may be helpful if the cervix is short in women with history suggesting cervical incompetence. Cerclage may not be helpful in those women who have a short cervix without a history of incompetence.

The ACOG Practice Bulletin on Cerclage for the Management of Cervical Insufficiency in 2014 suggests cerclage placement may be indicated in women with a singleton pregnancy who have a history of one or more second trimester pregnancy losses with painless dilation and without labor or abruption placenta, history of prior cerclage for painless dilatation, and physical examination of cervical dilatation in the second trimester.5 (FIGURE 3)

 

Figure 3: Indications for cervical encerclage

 

ACOG level B recommendation mentions that cerclage may increase the risk of preterm birth in women with a twin pregnancy and an ultrasonographically detected cervical length less than 25mm and is not recommended.2

In all asymptomatic women, who present with membranes at or protruding past the external cervical os, an emergency cerclage should be considered to reduce the risk of preterm delivery. Insufficient evidence exists to assess whether progesterone and cerclage together have an additive effect in reducing the risk of preterm birth in women at high-risk for preterm birth.4 (FIGURE 4)

 

Figure 4: Summary of management of preterm labour

 

3. Other interventions

Other interventions, such as pharmacotherapy with indomethacin or antibiotics, activity restriction, or supplementation with omega-3 fatty acids are not recommended as clinical interventions for women with an incidentally diagnosed short cervical length4Management of these women includes reduction of activity level, work, or travel, relocation, increased surveillance, and administration of corticosteroids.3

CONCLUSION

Preterm labour is a multifactorial condition associated with a high risk of morbidity and mortality, particularly at early gestational ages. Prevention is directed towards identification of women at risk and comprises screening and treatment for bacterial.

REFERENCES

1. Errol R Norwitz. Progesterone Supplementation and the Prevention of Preterm Birth. Rev Obstet Gynecol. 2011 Summer; 4(2): 60–72. PMCID: PMC3218546
2. Romero R.  Vaginal progesterone to reduce the rate of preterm birth and neonatal morbidity: a solution at last.  Womens Health (Lond Engl).  2011 Sep;7(5):501-4.
3. SOGC Executive and council of the Society of Obstetrics and Gynecology of Canada. Clinical practice guidelines No-257. Ultrasonographic cervical length assessment in predicting preterm birth in singleton pregnancies. JOGC May 2011 pg486-499
4. Committee on Practice Bulletins—Obstetrics. American College of Obstetricians and Gynecologists. Practice bulletin no. 130: prediction and prevention of preterm birth. Obstet Gynecol. 2012;120(4):964-973
5.  American College of Obstetricians and Gynecologists.  ACOG Practice Bulletin No.142: Cerclage for the management of cervical insufficiency.  Obstet Gynecol.  2014 Feb;123(2 Pt 1):372-9.