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ACOG Practice Bulletin No. 38: Perinatal Care at the Threshold of Viability

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Abstract

The survival rate for extremely preterm or extremely low‐birth‐weight (LBW) newborns born at the threshold of viability (25 or fewer completed weeks of gestation) improved in the early 1990s, largely as the result of a greater use of assisted ventilation in the delivery room and surfactant therapy. Increased use of antenatal and neonatal corticosteroids also may have influenced survival rates (1–4). However, this improvement in survival has not been associated with an equal improvement in morbidity. The incidence of chronic lung disease, sepsis, and poor growth remains high and may even have increased. There is concern that the treatment of extremely preterm and extremely LBW newborns may result in unforeseen effects into adulthood (4,5), and that the neurodevelopmental outcome and cognitive function of extremely preterm and extremely LBW infants may be suboptimal (6–8). The purpose of this document is to describe the potential consequences of extremely preterm birth and to provide clinical management guidelines based on the best available data.

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Background and Research Limitations

Early preterm birth or birth of an extremely LBW newborn (< 1,000 g), especially those weighing less than 750 g, poses a variety of complex medical, social, and ethical considerations. The impact of such births on the infants, their families, the health care system, and society is profound. Although the prevalence of such births is less than 1%, they account for nearly one half of all cases of perinatal mortality (9). Until recently, discussion of clinical management and ethical and economic considerations of extremely preterm births were hampered by conflicting and insufficiently detailed outcome data (1,3,4).

Although early reports on birth outcomes before 26 weeks of gestation often were helpful in counseling patients, most reports had one or more relative weaknesses that limited their clinical value. For example, denominators differed from study to study, being reported variously as all births (stillbirths and liveborns), only liveborns, or only liveborns who survived long enough to be admitted to a neonatal intensive care unit. Potential survival may be overstated by as much as 100% at 23 weeks of gestation and by 56% at 24 weeks of gestation if the denominator included only infants admitted to the neonatal intensive care unit instead of using all fetal deaths and live births (10). The length of time that constituted survival also varied widely. Many studies failed to obtain complete outcome data, and children from lower socioeconomic backgrounds were more likely to be lost to follow‐up.

Until the 1990s, when ultrasonography became more widely used, outcomes were largely reported only in terms of birth weight because of the uncertainty of gestational age. Studies based on birth weight were confounded by the inclusion of infants with intrauterine growth restriction (11); such newborns exhibited neurodevelopment consistent with their age and not their weight and, therefore, had an advantage when compared with newborns of the same size who were gestationally less mature (12,13). Studies based on gestational age also could be inaccurate; use of the Ballard estimate of gestational age at birth consistently yields an age 10 days older than the age determined by the best obstetric estimate (14). In addition, the influence of sex on survival rates was rarely considered.

Data derived from many years of experience in caring for patients at a single institution often were limited by small numbers of infants, with few representatives among the lowest birth weight categories. In addition, many series included infants cared for over a relatively long time, during which many changes in management practices were likely. For these reasons, it is controversial whether individual institutions should use their own data on morbidity and survival rates for extremely preterm and extremely LBW births when counseling patients and their families. All of these concerns are important because at the threshold of viability, gestational age, weight, sex, and management are each important determinants of survival.

Information from large multicenter studies, such as those sponsored by the National Institute of Child Health and Human Development (NICHD), provides sufficiently detailed data to assist the perinatal team in developing an evidence‐based approach to managing the extremely preterm and extremely LBW fetus. Data from the NICHD Neonatal Research Network are divided into subgroups based on gestational age in weeks or birth weight. Data by week of gestation are particularly important for these newborns because even a few days difference in age can be associated with a dramatic difference in expected outcome. Death and disability rates are inversely related to gestational age in newborns at 22–25 completed weeks of gestation (9,15,16).

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Clinical Considerations and Recommendations

How should the patient and her family be counseled about the likelihood of survival of an extremely preterm or extremely LBW infant?

An effort should be made to provide patients with information specific to the gestational age, estimated weight, and sex of their fetus. A multidisciplinary team approach to counseling may be helpful in ensuring that the information provided is consistent and represents a range of concerns and areas of clinical care. Counseling from a practitioner with additional experience and expertise in extremely preterm and extremely LBW births may be appropriate.

Data are now available from the most recent NICHD Neonatal Research Network trial, a large prospective study of 4,633 infants weighing between 400 g and 1,500 g at birth, conducted at 14 tertiary centers across the United States between 1995 and 1996 (14). In this study, gestational age was determined by the best obstetric estimate, using last menstrual period, standard obstetric parameters, and ultrasound examination. All liveborn infants were included, including those not admitted to the neonatal intensive care unit. Because mortality was defined as death occurring before patient discharge, the reported rates do not include deaths during labor or deaths after 120 days of life; conversely, survival rates refer to those infants who lived to at least 120 days. This study showed that a significant increase in survival of newborns occurs for each completed week from 21 weeks of gestation (0% survival) to 25 weeks of gestation (75% survival) (Table 1). In terms of birth weight (Table 2), survival was 11% at a birth weight of 400 g, 26% at birth weights of 500–601 g, and increased progressively to 75% at birth weights of 701–800 g (14). Infants delivered before 24 weeks of gestation (ie, up to 23 6/7 weeks) were not likely to survive, and those that did survive were not likely to be neurologically intact.

Table 1
Table 1
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Table 2
Table 2
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When gestational age, birth weight, and sex are combined (Fig. 1), it becomes evident that at each gestational age, a lower birth weight carries a higher mortality risk. This effect is most pronounced in the lower ranges of gestational age and birth weight. In addition, when infants of similar gestational age and weight are compared, mortality rates are higher for males than for females. For example, a male born at 24 weeks of gestation weighing 700 g has a predicted mortality rate of 51%, whereas a female of the same age and weight has a predicted mortality rate of 35% (14).

Figure 1
Figure 1
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These data apply to liveborn infants. Many of the smallest infants do not survive labor, do not respond to resuscitation, or are so small that resuscitation in the delivery room is not attempted. Among those who survive resuscitation in the delivery room, most deaths occur within the first 3 days of life (15,16). It is significant that the small proportion of infants weighing less than 500 g who do survive resuscitative efforts in the delivery room usually are female, small‐for‐gestationalage newborns (4).

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How should patients and their families be counseled about the morbidity associated with extremely preterm or extremely LBW infants?

Two recent large, prospective studies addressing morbidity —one using gestational age and one using birth weight—provide useful data. A gestational‐age‐based population study of 811 extremely preterm newborns used data collected in 1995 and found that disabilities in mental and psychomotor development, neuromotor function, or sensory and communication function were present in about one half of the large cohort of survivors at 30 months of corrected age (16). Approximately one quarter met the criteria for severe disability (16). Male newborns had lower psychomotor scores and were significantly more likely to have cerebral palsy than female newborns. A similar disadvantage for male newborns has been reported by others (2,17).

The most recent NICHD Neonatal Research Network study, which used data based on the birth weights of infants delivered at 14 tertiary care centers, reported similar results. Of all infants weighing 501–750 g, 100% had growth failure, 50% had intraventricular hemorrhage, 25% had grades III‐IV intraventricular hemorrhage, and 78% had respiratory distress syndrome (RDS) (14). The major morbidities influencing later development in these children included chronic lung disease, severe brain injury (intraventricular hemorrhage and periventricular leukomalacia), necrotizing enterocolitis, nosocomial infections, and retinopathy of prematurity.

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What are the risk factors for cerebral palsy at the threshold of viability?

A study from the NICHD Neonatal Research Network provided the first multicenter, prospective outcome data regarding the neurodevelopmental, neurosensory, and functional outcome of 1,151 extremely LBW newborns evaluated from birth to 18–22 months corrected age (Table 3) (2). Importantly, the sample size was sufficient to overcome some of the limitations that hampered the clinical applicability of earlier longitudinal outcome studies. One quarter of the children had an abnormal neurologic examination, approximately one third had a Bayley II Mental Development Index score less than 70 or a Psychomotor Developmental Index score less than 70 (normal for both these indices is >80), and 10% had visual or hearing impairment. Significant risk factors associated with cerebral palsy were grades III‐IV intraventricular hemorrhage, periventricular leukomalacia (odds ratio [OR], 3.05), and necrotizing enterocolitis (OR, 2.01). Risk factors for abnormal neurologic examination or Mental Development Index or Psychomotor Developmental Index scores less than 70 included grades III‐IV intraventricular hemorrhage, periventricular leukomalacia, chronic lung disease, use of postnatal steroids, necrotizing enterocolitis, a mother with less than a high school education, and male sex of the fetus.

Table 3
Table 3
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How does the assessment of gestational age affect counseling?

Gestational age often is well established. However, if gestational age is uncertain, it is important that the clinician consider a wide range of prognoses and care options and counsel the patient about a range of possible outcomes. Even relatively small discrepancies of 1 or 2 weeks in gestational age or 100–200 g in birth weight may have major implications for survival and long‐term morbidity.

In some cases—for example, in patients with little or no prenatal care—the gestational age is not established, and the clinician must consider data from fetal ultrasound measurements obtained near the time of anticipated delivery. Such measurements generally are not used to determine estimated gestational age unless they are the only data available. Although no single method has been determined to be superior, most ultrasound fetal weight formulas that include measurements of the fetal head, abdomen, and femur will yield a weight estimate within 15% of the actual weight (for weights <1,500 g) and a gestational age estimate within 2 weeks of the actual gestational age (from 20 to 30 weeks) (18). If there is a discrepancy of 2 weeks or more between the age based on menstrual dating and the age based on ultrasound measurements, or the woman is uncertain about the date of her last menstrual period, the physician may decide to make management decisions based on the ultrasound measurements, especially if measurements indicate a gestational age older than previously thought. If the measurements suggest a younger fetus, the possibility that the fetus is growth restricted should always be considered.

Ultrasonography also may provide useful information regarding the presence or absence of fetal malformations that may alter the prognosis of the fetus. However, fetal measurement and anatomic evaluation can be difficult in cases of multiple gestation or reduced amniotic fluid volume. Evaluation of multiple gestation also can be problematic because the prognosis for one infant may differ from that of the other(s).

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Does the mode of delivery affect neonatal outcome?

Few studies have evaluated the influence of obstetric management on the outcome of infants at the threshold of viability. Retrospective, nonrandomized studies have consistently failed to document a benefit of cesarean delivery for the extremely preterm fetus (19–23). It has even been difficult to document improved outcome with cesarean delivery for the extremely preterm fetus in breech position (20,21,24).

No prospective randomized studies of antenatal transfer of the extremely LBW infant to a tertiary care center have been reported. Retrospective data are difficult to analyze because the rapidity of labor, the severity of antepartum complications and the stability of the mother, the distance to the nearest high‐risk nursery, and other factors all influence transfer decisions. However, data from retrospective studies have demonstrated a decreased mortality risk for very LBW infants delivered at hospitals with a level III neonatal intensive care unit compared with delivery at hospitals with level I or level II neonatal intensive care units (25,26). Therefore, based on limited data, maternal transport to a tertiary care center should be considered when possible.

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Is there a benefit to the use of antenatal corticosteroids for extremely preterm births?

Although antenatal corticosteroids decrease the incidence of RDS in newborns at 29–34 weeks of gestation, randomized controlled trials have not shown a benefit in newborns treated between 24 and 28 weeks of gestation (27). In the largest randomized trial conducted on patients with intact membranes at 24–28 weeks of gestation, there was no benefit in the overall incidence or severity of RDS, but there was a significant reduction in the incidence of grades III and IV intraventricular hemorrhage (P = 0.01) (28). Although the precise impact of corticosteroids on RDS in pregnancies between 22 and 25 weeks of gestation has not been fully determined, the National Institutes of Health consensus conference statements on antenatal corticosteroid use recommended that all pregnant women at risk of preterm delivery between 24 and 34 weeks of gestation be considered candidates for a single course of corticosteroids (27,29).

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What are the current recommendations and ethical considerations regarding resuscitation and continued support of the extremely preterm fetus?

Ethical decisions regarding the extent of resuscitative efforts and the subsequent support of the neonate are complex (30–32). The decision to withhold or withdraw support should not be made entirely on the basis of gestational age or birth weight, but should be individualized based on the newborn's condition at birth, survival and morbidity data, and the parents' preferences.

Each member of the health care team should make every effort to maintain a consistent theme in their discussions with family members regarding the assessment, prognosis, and recommendations for care. However, parents should understand that decisions about neonatal management made before delivery may be altered depending on the condition of the neonate at birth, the postnatal gestational age assessment, and the newborn's response to resuscitative and stabilization measures. It also is important that parents understand that the outcome depends on many factors (such as infection), some of which may not be obvious before delivery or even at the time of resuscitation. Recommendations regarding the extent of continuing support depend on frequent reevaluations of the neonate's condition, trends, and prognosis. The course of an individual newborn may change with time.

There are circumstances in which the withdrawal of life support may be appropriate, recognizing that the views of the parents are of prime importance. Compassionate care should be provided to the infant, including careful handling, maintenance of a neutral thermal environment, and gentle monitoring of vital signs.

Because it is difficult to predict how an individual extremely preterm newborn will develop, proactive programs to assess and support the infant through early school years are desirable (4). When the extremely preterm newborn does not survive, support should be provided to the family by physicians, nurses, and other staff after the infant's death. Perinatal loss support groups, intermittent contact by telephone, and a later conference with the family to review the medical events surrounding the infant's death and to evaluate the grieving response of the parents often are helpful.

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Summary of Recommendations

The following recommendations are based on good and consistent scientific evidence (Level A):

▸ In general, parents of anticipated extremely preterm fetuses can be counseled that the neonatal survival rate for newborns increases from 0% at 21 weeks of gestation to 75% at 25 weeks of gestation, and from 11% at 401–500 g birth weight to 75% at 701–800 g birth weight. In addition, females generally have a better prognosis than males.

▸ In general, parents of anticipated extremely preterm fetuses can be counseled that infants delivered before 24 weeks of gestation are less likely to survive, and those who do are not likely to survive intact. Disabilities in mental and psychomotor development, neuromotor function, or sensory and communication function are present in approximately one half of extremely preterm fetuses.

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The following recommendations are based on limited or inconsistent scientific evidence (Level B):

▸ Based on data from retrospective studies, maternal transport to a tertiary care center before delivery should be considered when possible.

▸ The effects of aggressive resuscitation at birth on the outcome of the extremely preterm fetus also are unclear. Therefore, management decisions regarding the extremely preterm fetus must be individualized.

▸ The effect of antenatal steroid use in the extremely preterm fetus is unclear; however, it is recommended that all women at risk of preterm delivery between 24 and 34 weeks of gestation be considered candidates for a single course of corticosteroids.

▸ Prospectively collected outcome data for extremely preterm fetuses are available. Whenever possible, data specific to the age, weight, and sex of the individual extremely preterm fetus should be used to aid management decisions made by obstetricians and parents of fetuses at risk for preterm delivery before 26 completed weeks of gestation. This information may be developed by each institution and should indicate the population used in determining estimates of survivability.

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The following recommendations are based primarily on consensus and expert opinion (Level C):

▸ When extremely preterm birth is anticipated, the estimated gestational age and weight should be carefully assessed, the prognosis for the fetus should be determined, and each member of the health care team should make every effort to maintain a consistent theme in their discussion with family members regarding the assessment, prognosis, and recommendations for care.

▸ Because it is difficult to predict how an individual extremely preterm newborn will develop, proactive programs to assess and support the infant through early school years are desirable. When the extremely preterm newborn does not survive, support should be provided to the family by physicians, nurses, and other staff after the infant's death.

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References

1. Cole FS. Extremely preterm birth—defining the limits of hope. N Engl J Med 2000;343:429-30. (Level III)

2. Vohr BR, Wright LL, Dusick AM, Mele L, Verter J, Steichen JJ, et al. Neurodevelopmental and functional outcomes of extremely low birth weight infants in the National Institute of Child Health and Human Development Neonatal Research Network, 1993-1994. Pediatrics 2000;105:1216-26. (Level II-2)

3. McCormick MC. Conceptualizing child health status: observations from studies of very premature infants. Perspect Biol Med 1999;42:372-86. (Level III)

4. Hack M, Fanaroff AA. Outcomes of children of extremely low birthweight and gestational age in the 1990's. Early Hum Dev 1999;53:193-218. (Level III)

5. Hack M, Flannery DJ, Schluchter M, Carter L, Borawski E, Klein N. Outcomes in young adulthood for very-low-birth-weight infants. N Engl J Med 2002;346;149-57. (Level II-2)

6. Hack M, Taylor HG, Klein N, Eiben R, Schatschneider C, Mercuri-Minich N. School-age outcomes in children with birth weights under 750 g. N Engl J Med 1994;331:753-9. (Level II-2)

7. Hack M, Friedman H, Fanaroff AA. Outcomes of extremely low birth weight infants. Pediatrics 1996;98: 931-7. (Level II-3)

8. Peterson BS, Vohr B, Staib LH, Cannistraci CJ, Dolberg A, Schneider KC, et al. Regional brain volume abnormalities and long-term cognitive outcome in preterm infants. JAMA 2000;284:1939-47. (Level II-2)

9. Bottoms SF, Paul RH, Iams JD, Mercer BM, Thom EA, Roberts JM. Obstetric determinants of neonatal survival: influence of willingness to perform cesarean delivery on survival of extremely low-birth-weight infants. National Institute of Child Health and Human Development Network of Maternal-Fetal Medicine Units. Am J Obstet Gynecol 1997;176:960-6. (Level II-2)

10. Evans DJ, Levene MI. Evidence of selection bias in preterm survival studies: a systematic review. Arch Dis Child Fetal Neonatal Ed 2001;84:F79-84. (Level III)

11. Arnold CC, Kramer MS, Hobbs CA, McLean FH, Usher RH. Very low birth weight: a problematic cohort for epidemiologic studies of very small or immature neonates. Am J Epidemiol 1991;134:604-13. (Level II-3)

12. Pena IC, Teberg AJ, Finello KM. The premature small-for-gestational-age infant during the first year of life: comparison by birth weight and gestational age. J Pediatr 1988;113:1066-73. (Level II-2)

13. McCarton CM, Wallace IF, Divon M, Vaughan HG Jr. Cognitive and neurologic development of the premature, small for gestational age infant through age 6: comparison by birth weight and gestational age. Pediatrics 1996;98: 1167-78. (Level II-2)

14. Lemons JA, Bauer CR, Oh W, Korones SB, Papile L, Stoll BJ, et al. Very low birth weight outcomes of the National Institute of Child Health and Human Development Neonatal Research Network, January 1995 through December 1996. NICHD Neonatal Research Network. Pediatrics 2001;107:E1. (Level III)

15. Stevenson DK, Wright LL, Lemons JA, Oh W, Korones SB, Papile LA, et al. Very low birth weight outcomes of the National Institute of Child Health and Human Development Neonatal Research Network, January 1993 through December 1994. Am J Obstet Gynecol 1998;179: 1632-9. (Level II-3)

16. Wood NS, Marlow N, Costeloe K, Gibson AT, Wilkinson AR. Neurologic and developmental disability after extremely preterm birth. EPICure Study Group. N Engl J Med 2000;343:378-84. (Level II-2)

17. Tin W, Wariyar U, Hey E. Changing prognosis for babies of less than 28 weeks gestation in the north of England between 1983 and 1994. Northern Neonatal Network. BMJ 1997;314:107-11. (Level III)

18. Hadlock FP, Harrist RB, Sharman RS, Deter RL, Park SK. Estimation of fetal weight with the use of head, body, and femur measurements—a prospective study. Am J Obstet Gynecol 1985;151:333-7. (Level II-2)

19. Hack M, Fanaroff AA. Outcomes of extremely low birth weight infants between 1982 and 1988. N Engl J Med 1989;321:1642-7. (Level II-3)

20. Malloy MH, Rhoads GG, Schramm W, Land G. Increasing cesarean section rates in very low-birth weight infants. Effect on outcome. JAMA 1989;262:1475-8. (Level II-2)

21. Malloy MH, Onstad L, Wright E. The effect of cesarean delivery on birth outcome in very low birth weight infants. National Institute of Child Health and Human Development Neonatal Research Network. Obstet Gynecol 1991;77:498-503. (Level II-2)

22. Worthington D, Davis LE, Grausz JP, Sobocinski K. Factors influencing survival and morbidity with very low birth weight delivery. Obstet Gynecol 1983;62:550-5. (Level II-2)

23. Kitchen W, Ford GW, Doyle LW, Rickards AL, Lissenden JV, Pepperell RJ, et al. Cesarean section or vaginal delivery at 24 to 28 weeks' gestation: comparison of survival and neonatal and two-year morbidity. Obstet Gynecol 1985;66:149-57. (Level II-2)

24. Gravenhorst JB, Schreuder A, Veen S, Brand R, Verloove-Vanhorick SP, Verweij RA, et al. Breech delivery in very preterm and very low birthweight infants in The Netherlands. Br J Obstet Gynaecol 1993;100:411-5. (Level II-3)

25. Phibbs CS, Bronstein JM, Buxton E, Phibbs RH. The effects of patient volume and level of care at the hospital of birth on neonatal mortality. JAMA 1996;276:1054-9. (Level II-3)

26. Yeast JD, Poskin M, Stockbauer JW, Shaffer S. Changing patterns in regionalization of perinatal care and the impact on neonatal mortality. Am J Obstet Gynecol 1998;178: 131-5. (Level II-3)

27. Effect of corticosteroids for fetal maturation on perinatal outcomes. NIH Consensus Statement 1994;12:1-24. (Level III)

28. Garite TJ, Rumney PJ, Briggs GG, Harding JA, Nageotte MP, Towers CV, et al. A randomized, placebo-controlled trial of betamethasone for the prevention of respiratory distress syndrome at 24 to 28 weeks' gestation. Am J Obstet Gynecol 1992;166:646-51. (Level I)

29. Antenatal corticosteroids revisited: repeat courses. NIH Consensus Statement 2000;17:1-18. (Level III)

30. Rhoden NK. Treating Baby Doe: the ethics of uncertainty. Hastings Cent Rep 1986;16:34-42. (Level III)

31. Lantos JD, Meadow W, Miles SH, Ekwo E, Paton J, Hageman JR, et al. Providing and forgoing resuscitative therapy for babies of very low birth weight. J Clin Ethics 1992;3:283-7. (Level II-2)

32. Allen MC, Donohue PK, Dusman AE. The limit of viability —neonatal outcome of infants born at 22 to 25 weeks' gestation. N Engl J Med 1993;329:1597-1601. (Level II-3)

The MEDLINE database, the Cochrane Library, and ACOG's own internal resources and documents were used to conduct a literature search to locate relevant articles published between between January 1985 and January 2001. The search was restricted to articles published in the English language. Priority was given to articles reporting results of original research, although review articles and commentaries also were consulted. Abstracts of research presented at symposia and scientific conferences were not considered adequate for inclusion in this document. Guidelines published by organizations or institutions such as the National Institutes of Health and the American College of Obstetricians and Gynecologists were reviewed, and additional studies were located by reviewing bibliographies of identified articles. When reliable research was not available, expert opinions from obstetrician‐gynecologists were used.

Studies were reviewed and evaluated for quality according to the method outlined by the U.S. Preventive Services Task Force:

I Evidence obtained from at least one properly designed randomized controlled trial.

II‐1 Evidence obtained from well‐designed controlled trials without randomization.

II‐2 Evidence obtained from well‐designed cohort or case‐control analytic studies, preferably from more than one center or research group.

II‐3 Evidence obtained from multiple time series with or without the intervention. Dramatic results in uncontrolled experiments could also be regarded as this type of evidence.

III Opinions of respected authorities, based on clinical experience, descriptive studies, or reports of expert committees.

Based on the highest level of evidence found in the data, recommendations are provided and graded according to the following categories:

Level A—Recommendations are based on good and consistent scientific evidence.

Level B—Recommendations are based on limited or inconsistent scientific evidence.

Level C—Recommendations are based primarily on consensus and expert opinion.

© 2002 The American College of Obstetricians and Gynecologists

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