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Preterm Labor

Quick recognition and management can prevent premature delivery.

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Preterm labor (PTL) is a serious condition that leads to premature delivery in almost one-fifth of all pregnant women who deliver in the United States.1 Premature delivery is the single most severe complication of PTL; it can significantly increase neonatal morbidity and mortality.1 Children born prematurely are at much higher risk for long-term developmental and chronic health issues.2 PTL and its associated complications can be avoided and mitigated with proper identification, treatment and preventive measures.

Diagnosis

The diagnosis of PTL is difficult because patients may present with vague symptoms typical in normal pregnancies.3 It is not unusual for NPs and PAs in emergency departments, women's health settings and family practice settings to encounter pregnant women who report painful uterine contractions, pelvic pressure, increased vaginal discharge or low back pain.4

Overlap in the presentation of normal pregnancy symptoms and PTL has resulted in an overdiagnosis of PTL in up to 40% of patients.4 Some studies suggest that the presence of contractions, pelvic pressure, increased vaginal discharge or low back pain is predictive of PTL when accompanied by the following: six or more contractions per hour; initial cervical dilation of 3 cm or more; cervical effacement of 80% or more; ruptured membranes; or vaginal bleeding.3 The initial approach to a symptomatic patient should focus on assessment for these predictive signs.

Clinicians can use a thorough clinical history and a sterile speculum exam to collect the information necessary to decide whether a symptomatic patient should be sent to a tertiary care facility or discharged home. A systematic approach to assessment should begin by confirming gestational age and estimated due date based on the patient's history. In the presence of PTL, this information will guide subsequent interventions.5

Uterine Contractions

For patients who present with contraction-like pains, gather the information necessary to distinguish between true and false labor. True labor contractions tend to originate in the lower back and steadily increase in frequency, duration and amplitude.6 False contractions do not occur in predictable intervals, nor do they get closer together or increase in strength. Rather, their intensity often changes with position or activity. False contractions originate in the abdominal region instead of the lower back.

Research shows that patients who experience six or more true labor contractions per hour are at greater risk for PTL.3 When contractions occur at 5-minute intervals, active labor is likely. 6

Premature Membrane Rupture

After collecting the patient's clinical history, assess her for vaginal bleeding and preterm rupture of membranes (PROM) with a sterile speculum exam. Patients with PROM often report a sudden gush of fluid with continued leakage.5 If the speculum exam reveals pooling of fluids, identify the presence of amniotic fluid. This determination can be made with the nitrazine or fern test. The nitrazine test relies on a pH strip to detect the increased vaginal pH that occurs in the presence of amniotic fluid. Results are compared to the normal vaginal pH of between 4.5 and 6.0.5 In the fern test, vaginal discharge is microscopically examined for the characteristic of fern-type crystallization of amniotic fluid.7

Cervical Change

Visualizing the cervix for dilation and effacement is also an important component of the sterile speculum exam. If cervical change has occurred, in particular effacement of more than 80% or dilation of more than 3 cm, the patient should be transported to a tertiary setting where further evaluation with transvaginal ultrasound and a fetal fibronectin test can be performed.7 Research has shown that patients with a positive fetal fibronectin test and a cervical length of less than 30 mm viewable on transvaginal ultrasound are at a higher risk of delivery within 7 days (44.7%).7

Threshold for Action

Patients who present with false labor contractions without PROM or cervical change evident on speculum exam can be sent home without being exposed to any unnecessary interventions. Patients with PROM and/or cervical effacement and dilation, however, should be transported to a tertiary facility equipped to monitor fetal heart tracing for evidence of distress and for further evaluation with ultrasonography.5

Clinicians should have a lower threshold for transporting patients with a history of PTL or a presentation suggestive of chlamydia or gonorrhea.5 Patients with sexually transmitted infection are seven times more likely to have PROM, therefore cervical cultures are recommended.5

Management

The most common approach to managing PTL is the prolongation of pregnancy in order to provide more maturation time for the fetus. This reduces the risk for neonatal morbidity and mortality.8-10

Tocolytic (anti-contraction) agents can delay delivery for up to a week from the start of treatment.8,9 Published research contains disagreement about a clear choice for first-line treatment. Previously, betamimetics were a first-line choice for PTL. They were associated with a high occurrence of adverse effects and had a comparable efficacy to other treatments, which led to a greater likelihood of discontinuation.8,11,12 Therefore, research for a better, cost-effective first-line treatment continued.8,11,12

Indomethacin demonstrates the best rates of tolerance in patients who respond to treatment, but use after 32 weeks increases the incidence of premature closure of fetal ductus arteriousus, limiting its usability.8,11

In terms of efficacy in delaying delivery, patients treated with nifedipine are more likely to stop experiencing contractions, but they may experience increased adverse effects such as necrotizing enterocolitis, intraventricular hemorrhage or neonatal jaundice.9,11 In addition, nifedipine requires a longer duration of treatment than indomethacin.9,11 One study suggested a treatment protocol of first using indomethacin, then moving on to nifedipine if contractions did not end.11

Although studies show the benefit of tocolytic medications for acute PTL, their ability to prolong pregnancy is not as clear. Some research has shown that nifedipine and betamimetics exhibit a greater likelihood of prolonging pregnancy, but research generally does not show that tocolytics consistently prolong pregnancy or improve outcomes over a longer period or to term.8,9,12 Longer treatment with terbutaline increases the likelihood of poor maternal outcomes such as mortality and cardiovascular events, making its utilization in the clinical setting questionable.12

Tocolytics alone may not be as beneficial as believed for PTL. Some studies have found the treatments do not reduce frequencies of birth acutely or long term, nor do they show significant improvements in newborn morbidity or mortality without use of other treatment.8,10 The use of tocolytics in PTL seems most beneficial when the drugs are acutely coupled with a supplementary treatment such as corticosteroids to mature fetal lungs and improve neonatal outcomes.7,10

Prevention       

Premature labor should be viewed as a condition with multiple etiologies. It is preventable if at-risk women are identified early.13 This approach allows pregnant women to be stratified into risk categories and managed appropriately.

Short cervical length (less than 25 mm) identified via transvaginal ultrasound (TVUS) can accurately predict PTL risk when determined between 18 and 22 weeks' gestation.13 In one study, pain (experienced in less than 2% of women examined) was the only adverse event related to TVUS,13 making it a safe and quick way of identifying women at risk for PTL in an ultrasound-equipped office.

Another factor for clinicians to consider is the role that comorbidities play in increasing PTL risk. One study suggests that comorbidities such as maternal hypertension, anemia and hemorrhage from placental abruption have the most impact on whether PTL begins.14

The education and counseling of patients about comorbidity control can start with a simple review of past medical history and patient medications. Measures that may be considered are switching antihypertensive medications to drugs that are generally safe for pregnancy; vitamin or nutritional supplementation; and avoidance of risky behaviors such as drug use or trauma.14

Progesterone can relax uterine smooth muscle over the course of pregnancy and therefore may decrease the incidence of PTL.15 At least one study documented a significant reduction in the number of women experiencing PTL when progesterone was administered intramuscularly or vaginally during pregnancy.15 Many studies of progesterone use to prevent PTL do not provide set guidelines, therefore it is important to note that the best route and dose for administration have not yet been determined.

It is increasingly clear that infection-induced inflammatory response is one of the strongest risk factors associated with PTL.16 One study examined the effect that prophylactic broad-spectrum antibiotics may have on reducing PTL in women with bacterial vaginosis (BV) or abnormal vaginal flora at less than 22 weeks' gestation.17 The researchers found that at less than 37 weeks' gestation, the administration of clindamycin to women with BV was of some benefit.17 These differences were only observed when patients took clindamycin orally rather than vaginally, suggesting systemic absorption is necessary for a therapeutic effect.

While it may seem prudent to give prophylactic antibiotics to all pregnant mothers at less than 22 weeks' gestation, it is important to weigh the benefit of clindamycin use compared to the risk of potential Clostridium difficile infection.

Daily relaxation therapy is a method of prevention that may be recommended after risk for PTL has been determined. Listening to a recorded relaxation program every day may prolong pregnancy and thus prevent PTL.18 In studies that examined relaxation therapy, pregnancy outcomes were assessed and a significant mean prolongation of pregnancy of about 14 days was observed, along with decreased incidence of extremely low birth weight and shorter NICU stays.18 Signs seem to point to relaxation techniques as a cost-effective and easy-to-implement method for decreasing preterm labor incidence.

Get Prepared

Preterm labor is a prevalent issue that NPs and PAs are likely to come across in practice. Patients who experience PTL symptoms may not present directly to their selected obstetrician, therefore clinicians in other settings must be knowledgeable in the diagnosis and treatment of this condition. Symptoms can be vague and nonspecific, but a thorough history and sterile speculum exam can help identify patients at increased risk. The detection of PTL allows clinicians to consider whether to administer tocolytics or to refer to facilities more equipped to monitor the woman and her fetus.

Clinicians in primary care settings should also have a workable knowledge of preventive strategies for PTL. This includes stratifying patients according to risk factors and comorbidities, use of preventive medications such as progesterone and antibiotics, and recommendation for daily relaxation therapy. Ultimately, the diagnosis, treatment and prevention of PTL depend on clinical judgment. Clinicians working with pregnant patients should always consider PTL diagnosis in symptomatic patients, individualize treatment to the situation at hand, and utilize considerate preventive practice to minimize the incidence of PTL in their practice.

References

1. Martin JA, et al. Births: final data for 2009. Natl Vital Stat Rep. 2011;60(1):1-70.

2. Di Renzo GC, et al. Guidelines for the management of spontaneous preterm labor: identification of spontaneous preterm labor, diagnosis of preterm premature rupture of membranes, and preventive tools for preterm birth. J Matern Fetal Neonatal Med. 2011;24(5):659-667.

3. Iams JD. Prediction and early detection of preterm labor. Obstet Gynecol. 2003;101(2):402-412. 4. Chao TT, et al. The diagnosis and natural history of false preterm labor. Obstet Gynecol. 2011;118(6):1301-1308.

5. Medina TM, Hill DA. Preterm premature rupture of membranes: diagnosis and management. Am Fam Physician. 2006;73(4):659-664.

6. Pates JA, et al. Uterine contractions preceding labor. Obstet Gynecol. 2007;110(3):566-569.

7. Sayres WG. Preterm labor. Am Fam Physician. 2010;81(4):477-484.

8. Haas DM, et al. Tocolytic therapy: a meta-analysis and decision analysis. Obstet Gynecol. 2009;113(3):585-594.

9. Conde-Agudelo A, et al. Nifedipine in the management of preterm labor: a systematic review and metaanalysis. Am J Obstet Gynecol. 2011;204(2):134.e1-e20.

10. Mercer BM, Merlino AA. Magnesium sulfate for preterm labor and preterm birth. Obstet Gynecol. 2009;114(3):650-668.

11. Kashanian M, et al. Comparison of the efficacy and adverse effects of nifedipine and indomethacin for the treatment of preterm labor. Int J Gynaecol Obstet. 2011;113(3):192-195.

12. Gaudet LM, et al. Effectiveness of terbutaline pump for the prevention of preterm birth. A systematic review and meta-analysis. PLoS ONE. 2012;7(2):e31679.

13. Mella MT, Berghella V. Prediction of preterm birth: cervical sonography. Semin Perinatol. 2009;33(5):317-324.

14. Auger N, et al. Association between maternal comorbidity and preterm birth by severity and clinical subtype: retrospective cohort study. BMC Pregnancy Childbirth. 2011;11:67.

15. Dodd JM, et al. Progesterone for the prevention of preterm birth: a systematic review. Obstet Gynecol. 2008;112(1):127-134.

16. Hitti J, et al. Vaginal indicators of amniotic fluid infection in preterm labor. Obstet Gynecol. 2001;97(2):211-219.

17. Lamont RF, et al. Treatment of abnormal vaginal flora in early pregnancy with clindamycin for the prevention of spontaneous preterm birth: a systematic review and metaanalysis. Am J Obstet Gynecol. 2011;205(3):177-190.

18. Chuang LL, et al. The effectiveness of a relaxation training program for women with preterm labour on pregnancy outcomes: a controlled clinical trial. Int J Nurs Stud. 2012;49(3):257-264.

 

Gianina Ferrer is a physician assistant in the emergency department at Coney Island Hospital in Brooklyn, N.Y. Robert Aromando is a physician assistant at Adult and Pediatric Urology of Hunterdon in Flemington, N.J. Keith Forlenza is a physician assistant who is in an intensive care unit residency at Winthrop Hospital in Mineola, N.Y. Jean Covino is an assistant clinical professor and the coordinator of physician assistant graduate studies at Pace University-Lenox Hill Hospital. The authors have completed disclosure statements and report no relationships related to this article.

 

 




     

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