Preterm Labor and Preterm Premature Rupture of Membranes
Dinez Swanson
Suzanne McMurtry Baird
Objectives
As you complete this module, you will learn:
The definition of preterm labor
Strategies to identify women at risk for preterm labor
How to recognize and treat early symptoms of preterm labor
Management of preterm labor, including the following:
Pharmacologic agents
Nursing implications.
Appropriate education for women in preterm labor
The definition of preterm premature rupture of membranes (PPROM)
Risks to the mother and fetus associated with PPROM
Management methods when PPROM occurs in a preterm pregnancy, including the following:
Chorioamnionitis
Expectant management options
The role of antibiotics for these patients
Priorities for nursing interventions in caring for the woman with PPROM
The role of steroid therapy in the prevention of neonatal complications
The use of magnesium sulfate for neuroprotection
Key Terms
When you have completed this module, you should be able to recall the meanings of the following terms. You should also be able to use the terms when consulting with other health professionals. The terms are defined in this module or in the glossary at the end of this book.
17-α-hydroxyprogesterone caproate (17P)
Bacterial vaginosis
β-Adrenergic agonist
β-Adrenergic receptor
Braxton Hicks contractions
Calcium channel blocker
Chorioamnionitis
Corticosteroid
Corticotropin-releasing hormone (CRH)
Fetal fibronectin (fFN)
Late preterm birth
Low birth weight
Neuroprotection
Preterm premature rupture of membranes (PPROM)
Preterm birth
Prostaglandins
Tocolytic therapy
Very preterm birth
This module reviews current information regarding spontaneous preterm labor (PTL) and preterm premature rupture of membranes (PPROM). Continuing research is constantly changing our understanding of the process leading to these events. There is very little evidence that any of the medical strategies or behavioral interventions that we use have had any significant impact on the prevention of PTL or reduction in the number of preterm births (PTBs). Nurses should stay informed of current evidence, understand recommended best practice, and provide diligent assessments in order for practice decisions to be based on proven strategies, optimize utilization of resources, and to avoid potentially harmful and unnecessary interventions.
Part 1 Preterm Labor and Birth
Epidemiology of Preterm Labor and Birth
A PTB is defined as the delivery of an infant at less than 37 weeks of gestation and account for 11.4% of live births in the United States.1 PTB, although declining in rate, remains a significant issue with an estimated 450,000 babies are born too soon every year (US).1,2 Improvements in the PTB rate since 2006 appear to be driven by reductions in late preterm births (LPTB), which increased rapidly between 1990 and 2006, peaking at 9.1% of live births.2
PTBs account for 85% of all perinatal morbidity and mortality.2 A 2007 report from the Institute of Medicine estimated the annual cost of PTB in the United States to be $26.2 billion or more than $51,000 per premature infant.3 Medical care services contributed $16.9 billion to the total cost and maternal delivery costs contributed another $1.9 billion.3 In terms of longer-term expenditures, early intervention services cost an estimated $611 million, whereas special education services associated with a higher prevalence of four disabling conditions among premature infants added $1.1 billion.3 It is estimated that lost household and labor market productivity associated with those disabilities contributed $5.7 billion.3 Significant racial disparities persist in PTBs. In 2013, the PTB rate among African American women was 16%, 13.1% for American Indian or Alaska Native, 11.3% for Hispanic women, 10.2% for Asian or Pacific Islander, and 10.5% for Caucasian women.1
Complications of PTB arise from immature organ systems that are not yet prepared to support life in the extrauterine environment. In general, the more immature a preterm infant is at birth, the higher likelihood of required life-sustaining treatments, medications, and cost. Possible adverse outcomes for preterm infants are presented in Table 10.1.
PTBs are classified as medically indicated to optimize outcomes for maternal and/or fetal conditions, spontaneous due to PTL with intact membranes, PPROM, or multiple gestations.5
Preterm Definitions
Preterm: Birth that occurs between 20 0/7 and 36 6/7 weeks’ gestation.4
Late Preterm: Birth that occurs between 34 0/7 and 36 6/7 weeks’ gestation.
Low Birth Weight: Birth weight less than 2,500 g (5 lb, 8 oz).
Very Low Birth Weight: Birth weight less than 1,500 g (3 lb, 4 oz).
Extremely Low Birth Weight: Birth weight below 1,000 g.
NOTE: Low birth weight is not considered in the definition for PTL since it does not take into account the gestational age.
The most common factors that increase the woman’s risk of PTL and birth are:
Prior PTB: Women who have had a previous PTB have approximately a 30% increased risk delivering prematurely in a subsequent pregnancy.
Current multifetal pregnancy: Multiple gestations are associated with a high risk of PTL and birth. In general, the rate of PTL and birth is statistically higher in multifetal pregnancies. Contributing to the rate of prematurity among women with multifetal pregnancies is the use of assisted reproductive technologies (ART), such as in vitro fertilization, embryo
transfer, and donor transfer. There is also a higher rate of spontaneous multiple gestations in women over the age of 35.
Fetal fibronectin (fFN) greater than 50 ng/mL between 22 and 34 weeks’ gestation.
Uterine/cervical abnormalities (which may be due to previous surgical procedures).
Cervical length less than 25 mm by transvaginal ultrasound (TVU) between 20 and 28 weeks’ gestation
Previous pregnancy with cervical insufficiency
Abnormal placentation
TABLE 10.1 NEWBORN COMPLICATIONS OF PRETERM BIRTH | |||||||||||||
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Other factors that may increase risk for PTL and birth include:
Interval between pregnancies
Less than 18 months
Greater than 59 months
Vaginal bleeding not associated with previa or abruption
Infection/inflammation
Bacterial vaginosis
Periodontal disease
Ethnicity
African Americans and American Indians
Age
Women younger than age 18
Women older than age 35 (more likely to have other conditions such as high blood pressure and diabetes that can cause complications requiring preterm delivery).
Lifestyle factors
Substance abuse, including alcohol consumption
Smoking
Inadequate maternal weight gain
Domestic violence, including physical, sexual, or emotional abuse
Lack of social support
Depression, anxiety, stress
Long working hours with long periods of standing
Exposure to certain environmental pollutants
What Causes PTL
The initiation of labor involves two interdependent processes, that is, the triggering of rhythmic contractions that increase in amplitude and frequency, and the remodeling, effacement, and eventual dilatation of the cervix (with or without membrane rupture).4,5,6,7 There are four pathways that lead to spontaneous PTL and birth, with the ultimate cause most likely some combination of these physiologic pathways (Fig. 10.1). Prostaglandins are key components to the labor process that:
increase the number of contractions by stimulating the influx of calcium ions into smooth muscle cells.
improve coordination of uterine muscle contraction by increasing the number of gap junctions between the individual myometrial (uterine muscle) cells.
used in the production of proteases necessary for cervical ripening.
 FIGURE 10.1 Pathways to preterm labor. PTSD, post traumatic stress disorde. (From Simhan, H., Iams, J., & Romero, R. (2012). Preterm labor. In Gabbe, S. G., Niebyl, J. R., Simpson, J. L., et al. (Eds.), Obstetrics: Normal and problem pregnancies (6th ed., pp. 627–658). Philadelphia, PA: Saunders Elsevier; Cunningham, F., Leveno, K., Bloom, F., et al. (2013). Preterm labor. In Williams obstetrics (24th ed., pp. 829–861). New York, NY: McGraw Hill; American College of Obstetricians and Gynecologists, Committee on Practice Bulletins—Obstetrics. (2012). ACOG practice bulletin no. 127: Management of preterm labor. Obstetrics & Gynecology, 119(6), 1308–1317.) |
Inflammation and Infection
Infection and inflammation are associated with the maternal or fetal cytokine response, which in turn produces prostaglandins and stimulates the production of matrix-degrading enzymes that cause breakdown of fetal membranes. Inflammation and infection may remain localized in a particular tissue or area of the body, pass into circulating blood, or ascend to the fetal membranes and fetus. Fetal inflammatory response syndrome (FIRS) is systemic inflammation and has been strongly linked to PTB, intracranial hemorrhage, periventricular leukomalacia,
and cerebral palsy.8 This fetal process is thought to be caused by the production of cytokines (tumor necrosis factor, interleukins 1, 6, and 8) which stimulate PTL. Blood vessels in the premature fetal brain are weak and susceptible to rupture and damage. In addition, the cytokines released due to inflammation have a damaging effect on oligodendrocytes and myelin, resulting in neuron death.5
and cerebral palsy.8 This fetal process is thought to be caused by the production of cytokines (tumor necrosis factor, interleukins 1, 6, and 8) which stimulate PTL. Blood vessels in the premature fetal brain are weak and susceptible to rupture and damage. In addition, the cytokines released due to inflammation have a damaging effect on oligodendrocytes and myelin, resulting in neuron death.5
Two micro-organisms that have been strongly linked to PTL and birth are Ureaplasma urealyticum and Mycoplasma hominis. Both organisms are thought to ascend from the lower genital tract. Bacterial vaginosis (BV) is associated with a twofold increase in PTL and a variety of other obstetric complications such as spontaneous abortion, chorioamnionitis, and low birth weight.9 BV is a vaginal flora imbalance that occurs when the normal lactobacillus bacteria are replaced with anaerobic bacteria such as Gardnerella vaginalis, Mobiluncus, or Mycoplasma hominis. Women who are under chronic stress conditions, of certain ethnic groups, or who use vaginal douches have an increased risk of BV. Women with BV will have a watery and/or malodorous vaginal discharge. Screening and treatment have not been associated with a decreased risk of PTB. Routine screening is not recommend, but women who are symptomatic and diagnosed with an infection should be treated.6
Other infections, not associated with the genital tract, are also associated with PTL and birth. Urinary tract infections (cystitis, pyelonephritis), appendicitis, and periodontal disease increase risk. The pathophysiologic mechanisms are not well understood but are most likely linked to the maternal or fetal immune response. The woman’s cervical length may also determine the effect of the infection and outcomes.10
Maternal or Fetal Stress
It has been suggested that stress stimulates the maternal–fetal hypothalamic–pituitary–adrenal axis. This in turn can cause increased production of corticotropin-releasing hormone (CRH). CRH is linked to cytokine release and prostaglandin production. Abnormal or early elevations of these hormone levels in maternal plasma have been documented in PTL. However, studies have not consistently shown the connection between stress, increased levels of CRH, and PTB.5,11 A recent study indicated that pregnant women with posttraumatic stress disorder are at increased risk of PTB and should be treated as having high-risk pregnancies.12 Further studies are needed to explain how stress may affect different women or why some women in very stressful situations deliver at term.
Decidual Hemorrhage or Abruption
Decidual hemorrhage or abruption initiates the coagulation cascade and production of thrombin. Thrombin has a uterotonic effect resulting in cervical ripening, uterine contractions, and a breakdown of the fetal membranes.13 Any amount of vaginal bleeding between 6 and 13 weeks’ gestation is associated with increased risk of pregnancy loss (before 24 weeks’ gestation), abruption, and PTL.14
Mechanical Stretch of the Uterus
Another pathway of PTL is associated with overdistention of the uterus causing excessive uterine stretching in multifetal pregnancies, certain uterine malformations, macrosomia, or the development of polyhydramnios. The abnormal uterine stretching can stimulate prostaglandin production, thereby creating contractions. The mechanisms by which uterine overdistension might lead to PTL are not well understood. Uterine stretch induces the expression of gap junction proteins, as well as other contraction-associated proteins, such as oxytocin receptors. In multifetal pregnancies, a short cervical length (less than 25 mm) is the strongest risk factor for spontaneous PTB.15,16
What are the Warning Signs of PTL?
The early warning signs of PTL are often subtle and can be difficult to differentiate from routine discomforts of pregnancy. These warning signs may go unrecognized until labor is advanced. The key to treating PTL and potentially preventing some of the morbidity associated with an early delivery is early recognition and treatment. Pregnant women should be educated to recognize the following symptoms6:
Change in type of vaginal discharge (watery, mucus, or bloody)
Increase in amount of discharge
Pelvic or lower abdominal pressure
Constant low, dull backache
Mild abdominal cramps, with or without diarrhea
Regular or frequent contractions or uterine tightening, often painless
Ruptured membranes (your water breaks with a gush or a trickle of fluid)
NOTE: A woman in PTL may have only one or all of these signs. The woman experiencing one or more of the signs of PTL should be examined and evaluated promptly.
In addition to educating women and their families, all providers who might have contact with pregnant women should be knowledgeable about the early symptoms of PTL and the appropriate response. It is important to ensure the woman understands the terms used and can describe her symptoms. The importance of prompt reporting of these symptoms should be emphasized. The risks of delaying evaluation and treatment should be made clear, and women should be made to feel comfortable reporting symptoms or coming in for further evaluation, even when they are found not to be in labor.
NOTE: Before giving instructions, the woman’s knowledge level of PTL, her pregnancy history, and distance from the hospital should be ascertained.
Assessment for Preterm Labor
Better identification of women in PTL not only provides timely and appropriate interventions but also promotes effective management to improve outcomes. Obstetric triage protocols should standardize assessment parameters according to best practice recommendations and prioritize the medical screening examination when a woman presents with PTL symptoms (Fig. 10.2). Units should establish a standardized clinical pathway for the assessment of women with suspected signs and symptoms of PTL, guidelines for management of asymptomatic women at risk of PTB, and management of women with confirmed PTL.17 Early differentiation between “true” and “false” labor allows for timely decisions regarding management, which may include transport to a higher level of care, administration of antenatal corticosteroids and/or tocolytics, and assembly of the high-risk team. While it may not be possible to decrease the rate of PTB for these women, the outlined standardized interventions are well established to significantly improve neonatal outcomes.
 FIGURE 10.2 Triage of preterm labor. (From American College of Obstetricians and Gynecologists, Committee on Practice Bulletins—Obstetrics. (2012). ACOG practice bulletin no. 127: Management of preterm labor. Obstetrics & Gynecology, 119(6), 1308–1317; March of Dimes. (2012). Preterm labor assessment toolkit. White Plains, NY: Author. Retrieved from https://www.prematurityprevention.org/portal/server.pt; Howard, E. (2013). Labor evaluation. In Angelini, D., & LaFontaine, D. (Eds.), Obstetric triage and emergency care protocols (pp. 159–167). New York, NY: Springer Publishing.) |
Spontaneous PTL, which accounts for approximately 50% of PTBs, is defined as regular uterine contractions occurring between 20 and 36 6/7 weeks’ gestation accompanied by one or more of the following2,6:
Change in cervical dilation AND/OR change in cervical effacement (assessment by digital examination or TVU).
OR
Initial assessment of cervical dilation of 2 cm or more.
Timely and appropriate patient assessment by the nurse and provider is crucial to identify women at risk for PTB (Table 10.2). Preterm uterine contractions are not a reliable assessment parameter to determine if a woman is in PTL. Preterm contractions may be described as irregular or painless. A qualified medical provider should complete a thorough review of the woman’s symptoms, prenatal record, and history soon after the woman presents and per Emergency Medical Treatment Labor Act (EMTALA) regulation.6,17,18,19
NOTE: If serial cervical examinations are indicated, ideally they should be done by the same examiner, when possible, to improve reliability of assessing early or subtle cervical change.
What Tests are Used to Diagnose Preterm Labor?
Specific and objective diagnostic tools allow safe and cost-effective evaluation of women who present with uterine contractions without cervical change (a low-threshold sign and symptom of PTL). Current diagnostic tools include the fFN test and TVU for cervical length measurement. In combination with an fFN test result, cervical length more accurately predicts the likelihood of premature birth. However, either screen alone has also been found to distinguish between symptomatic patients at high and low risk for PTB.18 Providers should use standardized criteria and protocols to identify those women at risk for having a PTB in order to reduce unnecessary hospitalizations and medical treatments, as well as the cost related to these interventions.
Fetal Fibronectin
fFN is a glycoprotein found in plasma produced by the fetus and that typically is present in maternal vaginal secretions.17 During weeks 22 to 35 of a normal pregnancy, it is virtually undetectable in vaginal secretions. However, if disruption of the maternal–fetal interface occurs fibronectin is released into cervical/vaginal secretions and is an indicator of increased PTB risk. A positive fFN test is a value greater than 50 ng/mL. The positive predictive value of testing for fFN is low, meaning that many women who have fFN will not go into PTL. However, the negative predictive value is high. This means that when fFN is not detected in vaginal secretions, there is a very high likelihood that a woman will not experience PTL within 14 days of the test making this an important tool to determine whether a woman with preterm contractions should be admitted and treated for PTL.20
When the woman has signs and symptoms of PTL, samples should be collected using a sterile speculum with the following best practice recommendations17:
between 24 and 34 weeks’ gestation
there is no evidence of vaginal bleeding
the cervix is dilated less than 3 cm
fetal membranes are intact and not bulging
there are no open cervical and/or vaginal lesions present
intercourse or digital cervical examination has not occurred during the 24 hours prior to specimen collection
NOTE: Use of a sterile speculum for collection of fFN is the only FDA-approved method. Vaginal swab collection is no longer recommended.21
Cervical Length Measurement
Cervical length obtained by TVU is superior to digital assessment due to subjectivity of the examiner.17 The normal cervical length in the mid-trimester of pregnancy varies from 10 to 50 mm (median, 35 mm). When the cervix measures less than 25 mm in length by TVU, the woman has a greater than 95% risk for PTB before 32 gestational weeks. TVU should be done by an experienced provider in order to obtain accurate measurements. Contraindications and limitations of TVU for cervical length include22:
TABLE 10.2 SAMPLE TRIAGE AND INITIAL ASSESSMENT PLAN OF CARE | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Before 15 gestational weeks and after 28 gestational week measurements are considered invalid.
Vaginal bleeding is present, the cause of bleeding should be investigated prior to conducting a TVU.
Active bleeding from placenta previa. (If previa is not actively bleeding, an experienced operator who is aware of the woman’s condition and mindful that the procedure may provoke bleeding may perform TVU.)
A full bladder, as the cervix may be deviated in relation to the volume of fullness. A full bladder may also compress the cervix between the probe and the bladder, causing the cervix to appear closed or falsely long. Most women find it painful to undergo the procedure with a full bladder and, hence, should empty their bladders beforehand.
NOTE: Not all institutions or birth settings have experienced providers and availability of ultrasound equipment to provide screening.
Management of PTL
Management of women with PTL after triage and initial assessment is determined by the provider and based on gestational age, assessment findings, and hospital capabilities for care of preterm infants.
Gestational Age Between 34 0/7 and 36 6/7 Weeks of Pregnancy
There are many variables in management of the woman who presents in spontaneous PTL between 34 0/7 and 36 6/7 weeks’ gestation. To determine cervical change, serial digital examinations are indicated since fFN and TVU are not objective assessment tools in this gestational age group. Tocolytics are not indicated during this gestational age unless administration is for stabilization and transport to a tertiary care hospital.
Tocolytic Therapy
Tocolytic medications are used to slow down or halt uterine contractions in order for pregnancy to proceed so that the fetus can gain size and maturity before birth. Unfortunately, studies comparing the effectiveness of tocolytics to placebos and to each other have only shown short-term efficacy with no direct neonatal benefit.23 The focus of tocolytic therapy is to:
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