Objective
The purpose of this study was to determine whether corticosteroid administration after 34 weeks of gestation is associated with improved neonatal outcome in the presence of fetal lung immaturity.
Study Design
We conducted a retrospective cohort study of women who underwent amniocentesis to determine fetal lung maturity from 34-37 weeks of gestation. Patients with negative results (167 women) received steroids based on physician preference and were categorized into 2 groups: study group treated with betamethasone (n = 83 women) and control group in which patients did not receive betamethasone therapy (n = 84 women). The 2 groups were compared with respect to neonatal outcomes. Composite neonatal morbidity was defined as the presence of respiratory distress syndrome, transient tachypnea of the newborn infant, or the need for respiratory support.
Results
The rate of composite neonatal morbidity was significantly lower among infants who were exposed to steroids compared with the control group (8.4% vs 21%; P = .02). Multiple regression analysis revealed that corticosteroid administration was associated independently with the composite morbidity outcome.
Conclusion
Antenatal steroid administration after 34 weeks of gestation is associated with improved neonatal outcome and should be considered when fetal lung immaturity is documented.
The proportion of late preterm infants, defined as those born from 34-36 weeks of gestation among US singleton live births, increased by 11.6% between 1992 and 2002. Currently, late preterm births account for approximately 75% of all preterm births. This increase is attributed mostly to the increase in obstetric interventions because of maternal or fetal complications such as preeclampsia, diabetes mellitus, and fetal growth restriction.
The clinical decision whether to deliver a premature infant is determined by the balance between the risk of death and morbidity that is associated with prematurity on one hand and the assessment of maternal and fetal well-being should induction of labor be deferred on the other hand.
Although the risk for neonatal death and morbidity among late preterm infants is lower than those infants who are born at <34 weeks of gestation, late preterm infants are at greater risk for newborn morbidity compared with term infants. A compelling body of evidence has suggested that late prematurity is associated with feeding difficulty, body temperature instability, late neonatal sepsis, prolonged physiologic jaundice, hypoglycemia, and respiratory problems compared with a term infant. In a large retrospective cohort study that included 133,022 singleton live births, all of the studied measures of adverse neonatal outcome at 34, 35, 36, and 37 weeks of gestation were significantly increased compared with births at 39 weeks of gestation, especially respiratory distress, sepsis work-ups, and hyperbilirubinemia. Medical interventions that potentially can improve the outcome of late preterm infants include the use of tocolytics to delay delivery and the administration of corticosteroids to promote fetal lung maturation. However, the beneficial effect of corticosteroids in the prevention of respiratory distress in preterm infants has been shown to be limited to births at <34 weeks of gestation. Consequently, the American College of Obstetricians and Gynecologists has recommended that corticosteroids should be administered to pregnant women who are at risk for preterm delivery only at <34 weeks of gestation. The use of corticosteroids at >34 weeks of gestation is not recommended according to the American College of Obstetricians and Gynecologists, unless there is evidence of fetal pulmonary immaturity.
The assessment of fetal lung maturity might be useful for determination of the timing of delivery in patients with complicated pregnancies, in which continuing pregnancy may impose risk to either the mother, the fetus, or both. Although a mature fetal lung maturity test usually will lead to the induction of labor, there is no consensus as to the right management after an immature result. Scientific data regarding the clinical effect of steroid administration in the presence of documented fetal lung immaturity results at >34 weeks of gestation are limited. Therefore, the aim of this study was to determine whether antenatal glucocorticoid administration at >34 weeks of gestation is associated with improved neonatal outcome in the presence of documented fetal lung immaturity.
Materials and Methods
This is a retrospective cohort study of pregnant women who underwent amniocentesis to determine fetal lung maturity at 34-37 weeks of gestation. All women received prenatal care and delivered at a tertiary medical center between January 2006 and July 2011. The study was approved by the Institutional Research Ethics Board of Sheba Medical Center.
Fetal lung maturity was determined by fluorescence polarization (TDx-FLM II); a TDx-FLM-II test result of <50 mg/g was defined as an immature test. Negative results were documented for 167 patients who comprised 2 groups: (1) study group in which patients were treated with 2 doses of betamethasone (12 mg) intramuscular injection 24 hours apart (n = 83 women) and (2) control group in which patients did not receive betamethasone therapy (n = 84 women). The decision whether to treat with antenatal steroids for lung maturity after an immature result was at the discretion of the attending physician. Patients with mature test results were excluded as were multiple gestations and pregnancies that were complicated by congenital anomalies or chromosomal abnormalities. The charts of all women and their infants were reviewed for the variables of interest. Maternal characteristics and their pregnancy outcomes were abstracted from the obstetric electronic charts. Gestational age was calculated on the basis of the last menstrual period and was correlated to a first trimester ultrasound examination.
The following neonatal outcomes were examined: respiratory distress syndrome (RDS), transient tachypnea of the newborn infant (TTN), need for respiratory support (continuous positive airway pressure or oxygen supplementation), admission to the neonatal intensive care unit, admission to the special care neonatal unit, hypoglycemia (documented glucose level, <45 mg/dL), hyperbilirubinemia that required treatment, sepsis that was confirmed by positive blood cultures, and length of hospitalization. The primary study outcome was defined as a composite respiratory morbidity outcome that included RDS, TTN, or a need for respiratory support. RDS was defined as early respiratory distress comprised of cyanosis, grunting, retractions, and tachypnea combined with ground glass appearance and air bronchograms on chest x-ray. TTN was defined as respiratory distress with prominent perihilar streaking and fluid in the interlobar fissures on chest x-ray. Respiratory support was given when babies had a PaO2 level of <50 mm Hg in room air, central cyanosis, or saturation of <90% in room air.
Normality of the data was tested with Shapiro-Wilk or Kolmogorov-Smirnov tests. Data are presented as median and interquartile range. Comparison of continuous variables between the 2 groups was conducted with the Mann-Whitney U test (or Student t test, as appropriate). χ 2 or Fisher exact test was used for comparison of categoric variables.
Linear regression analysis was used to determine which factors were significantly and independently correlated with the composite respiratory morbidity outcome. The following parameters were included in the model: maternal age, TDx-FLM-II test result, the presence of gestational diabetes mellitus, mode of delivery, gestational age at delivery, birthweight, sex, and treatment with betamethasone. Significance was accepted at a probability value of < .05. Statistical analyses were conducted with the IBM Statistical Package for the Social Sciences (IBM SPSS, version 19; IBM Corporation Inc, Armonk, NY).
Results
Of all the women who underwent amniocentesis for lung maturity during the study period, 167 had immature test results; 83 women were treated (study group) and 84 women were not treated (control group) with corticosteroids.
The major indications for amniocentesis and early delivery were distributed equally between the study and control groups and included bad obstetric history (20% vs 12%; P = .1), intrauterine growth restriction (16% vs 20%; P = .5), mild preeclampsia (13% vs 7%; P = .21), previous uterine T incision, rupture, or dehiscence (14% vs 8%; P = .2), and nonreassuring fetal monitor (4% vs 5%; P = 1.0). Clinical characteristics of the 2 study groups are given in Table 1 . There were no significant differences between the 2 groups with respect to maternal age, gestational age at amniocentesis, gestational age at delivery, and interval between amniocentesis and delivery. The cesarean delivery rate, birthweight, and the male/female ratio were also similar between the 2 groups. Although not statistically significant, the rate of patients with gestational diabetes mellitus was higher in the control group than in the study group (33% vs 19%, respectively; P = .053). Moreover, patients who received corticosteroid therapy had a significantly lower TDx-FLM-II value compared with patients who were not treated (29 vs 32.7 mg/g, respectively; P = .036). The rates of neonatal outcomes in both groups are given in Table 2 . The rate of the composite respiratory morbidity outcome was significantly higher in the nontreatment group compared with patients who received corticosteroid therapy (21% vs 8.4%, respectively; P = .02). Consistent with the aforementioned finding, significantly more infants in the nontreatment group required respiratory support (20% vs 8.4%, respectively; P = .03). In addition, the rate of admission to the special care unit was higher in the control than in the study group, although this difference did not reach statistical significance (29% vs 17% respectively; P = .07). The 2 groups did not differ significantly with regard to the rates of RDS, TTN, hypoglycemia, and hyperbilirubinemia. Multiple linear regression analysis was used to examine the contribution of treatment with antenatal corticosteroids to the composite respiratory morbidity outcome while adjustment was made for maternal age, TDx-FLM-II test result, the presence of gestational diabetes mellitus, mode of delivery, gestational age at delivery, birthweight, and sex ( Table 3 ). The final regression model revealed that corticosteroid administration (adjusted odds ratio [OR], 0.23; 95% confidence interval [CI], 0.07–0.78) and TDx-FLM-II value (adjusted OR, 0.9; 95% CI, 0.86–0.99) and gestational age at delivery (adjusted OR, 0.33; 95% CI, 0.2–0.55) were associated independently with the composite morbidity outcome.
| Variable | Steroids (n = 83) | No steroids (n = 84) | P value |
|---|---|---|---|
| Maternal age, y a | 33 (30–36) | 33 (30.25–36) | .7 |
| Gestational diabetes mellitus, n (%) | 16 (19) | 28 (33) | .053 |
| TDx-FLM-II, mg/g a | 29 (20–40.25) | 32.7 (25–41) | .036 |
| Gestational age at amniocentesis, wk a | 36 (35–36) | 36 (34–36) | .095 |
| Gestational age at delivery, wk a | 37 (36–37) | 36 (35.2–37) | .4 |
| Interval between amniocentesis to delivery, d a | 5 (3–7) | 7 (2–8) | .1 |
| Birthweight, g a | 2790 (2450–3137) | 2590 (2210–3008) | .17 |
| Male/female ratio | 1.15 | 1.3 | .87 |
| Cesarean section delivery, n (%) | 59 (71) | 52 (62) | .2 |
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