The Impact of Fetal Anomalies on Contemporary Labor Patterns.

OBJECTIVE: To compare labor patterns in pregnancies affected by fetal anomalies to low-risk singletons. STUDY DESIGN: Labor data from the Consortium on Safe Labor, a multicenter retrospective study from 19 U.S. hospitals, including 98,674 low-risk singletons compared with 6,343 pregnancies with fetal anomalies were analyzed. Repeated-measures analysis constructed mean labor curves by parity, gestational age, and presence of fetal anomaly in women who reached full dilation. Interval-censored regression analysis adjusted for covariables was used to determine the median traverse times for labor progression. RESULTS: Labor curves for all groups indicated slower labor progress for patients with fetal anomalies. The most significant trends in median traverse times were observed in the preterm nulliparous and term multiparous groups. The median traverse times from 4 cm to complete dilation in the preterm nulliparous control versus anomaly groups were 5.0 and 5.4 hours (p < 0.0001). CONCLUSION: Labor proceeds at a slower rate in pregnancies affected by anomalies.

SMFM Consult Series #46: Evaluation and management of polyhydramnios.

Polyhydramnios, or hydramnios, is an abnormal increase in the volume of amniotic fluid. Identification of polyhydramnios should prompt a search for an underlying etiology. Although most cases of mild polyhydramnios are idiopathic, the 2 most common pathologic causes are maternal diabetes mellitus and fetal anomalies, some of which are associated with genetic syndromes. Other causes of polyhydramnios include congenital infection and alloimmunization. The purpose of this document is to provide guidance on the evaluation and management of polyhydramnios. The following are Society for Maternal-Fetal Medicine recommendations: (1) we suggest that polyhydramnios in singleton pregnancies be defined as either a deepest vertical pocket of ≥8 cm or an amniotic fluid index of ≥24 cm (GRADE 2C); (2) we recommend that amnioreduction be considered only for the indication of severe maternal discomfort, dyspnea, or both in the setting of severe polyhydramnios (GRADE 1C); (3) we recommend that indomethacin should not be used for the sole purpose of decreasing amniotic fluid in the setting of polyhydramnios (GRADE 1B); (4) we suggest that antenatal fetal surveillance is not required for the sole indication of mild idiopathic polyhydramnios (GRADE 2C); (5) we recommend that labor should be allowed to occur spontaneously at term for women with mild idiopathic polyhydramnios; that induction, if planned, should not occur at <39 weeks of gestation in the absence of other indications; and that mode of delivery should be determined based on usual obstetric indications (GRADE 1C); and (6) we recommend that women with severe polyhydramnios deliver at a tertiary center due to the significant possibility that fetal anomalies may be present (GRADE 1C).

Antenatal Treatment with Intravenous Immunoglobulin to Prevent Gestational Alloimmune Liver Disease: Comparative Effectiveness of 14-Week versus 18-Week Initiation.

BACKGROUND: Antenatal therapy with high-dose intravenous immunoglobulin (IVIG) may prevent gestational alloimmune liver disease (GALD). OBJECTIVE: The objective of this study was to determine the effectiveness of this approach in a large cohort of women at risk for poor pregnancy outcome due to GALD. METHODS: Women with a history of affected offspring were provided antenatal IVIG treatment and data were acquired prospectively from 1997 to 2015. The outcomes of treated pregnancies were compared to those of untreated pregnancies, and the effectiveness of starting at 14 weeks was compared to that of starting at 18 weeks. RESULTS: A total of 188 treated pregnancies in 151 women were analyzed. Only 30% (n = 105) of untreated gestations resulted in healthy offspring as compared to 94% (n = 177) of treated pregnancies (p < 0.0001). Treated gestations of both the 14-week (n = 108) and the 18-week (n = 80) start cohort showed a decreased rate of fetal loss relative to untreated gestations (p < 0.0001). Equivalent outcomes were recorded in the 18-week versus the 14-week start cohort (p > 0.05). Few adverse events or complications of antenatal therapy were recorded. CONCLUSION: Antenatal therapy with high-dose IVIG initiated at either 18 or 14 gestational weeks effectively prevents poor outcome of pregnancies at risk for GALD.

Do Different Modes of Labor Induction Affect the Overall Success and Risk of Trial of Labor After Cesarean Section?

OBJECTIVE: To determine whether different modes of labor induction impact the success rate and perinatal morbidity in women undergoing trial of labor after cesarean (TOLAC). STUDY DESIGN: Retrospective review of the Consortium on Safe Labor electronic database from 2002�2008; women with a prior cesarean birth, desiring TOLAC, and requiring induction of labor were included. Oxytocin and Foley bulb induction methods were compared to amniotomy alone. Prostaglandin use was also reviewed but, given the small numbers, was not the focus of this study. RESULTS: Univariate analysis showed significantly greater incidence of hemorrhage >1,000 mL (p=0.0030) and transfusion (p=0.0076) with Foley bulb use. All methods of induction for TOLAC decreased repeat cesarean sections (OR 0.34, 95% CI 0.23�0.52, p<0.01). CONCLUSION: Induction of labor does not alter the success rate for TOLAC candidates, regardless of mode of induction. When choosing induction methods, one should be mindful of the apparent additional risk of increased blood loss and transfusion with intracervical Foley bulb usage.

Does Induction with Misoprostol Impact the Small for Gestational Age Neonate?

OBJECTIVE: To compare outcomes in small for gestational age neonates induced with misoprostol to other cervical ripening agents. We hypothesized that misoprostol use will demonstrate no significant difference in outcomes compared with alternative agents. STUDY DESIGN: Small for gestational age neonates (<10th percentile for gestational age) from the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) sponsored Consortium on Safe Labor database were analyzed. Neonates induced with misoprostol ± oxytocin (n = 451) were compared with neonates induced with prostaglandin E2 ± oxytocin and/or mechanical dilation ± oxytocin (n = 663). Primary outcomes included intrapartum fetal distress, cesarean section for fetal distress, cesarean section for any reason, neonatal intensive care unit admission, low 5-minute Apgar, and composite neonatal morbidity. Multiple logistic regression was used to calculate adjusted odds ratios (aORs). Data were analyzed using SAS. RESULTS: Small for gestational age neonates induced with misoprostol ± oxytocin compared with alternative agents had decreased low 5-minute Apgar scores (aOR 0.27 [0.10-0.71]). No significant differences were demonstrated among very small for gestational age neonates (<5th percentile for gestational age). CONCLUSION: Our results suggest that misoprostol does not increase risk of adverse outcomes in small for gestational age neonates; however, prospective studies are warranted to further assess optimal cervical ripening agents in this population.

Placenta previa: an outcome-based cohort study in a contemporary obstetric population.

OBJECTIVE: The objective of the study is to characterize the maternal and neonatal morbidities of women with placenta previa. STUDY DESIGN: This retrospective group study used the Consortium on Safe Labor electronic database, including 12 clinical centers, and 19 hospitals. Patients with placenta previa noted at the time of delivery were included. Maternal and neonatal variables were compared to a control group of women undergoing cesarean delivery with no previa. Logistic regression and general linear regression were used for the analysis, with p < 0.05 significance. RESULTS: There were 19,069 patients in the study: 452 in the placenta previa group and 18,617 in the control group. Neonates born to mothers with placenta previa had lower gestational ages and birth weights. In univariate analysis only, these neonates were at increased risk of lower 5 min Apgar scores, neonatal intensive care unit admission, anemia, respiratory distress syndrome, mechanical ventilation, and intraventricular hemorrhage. There was no association of placenta previa with small for gestational age infants, congenital anomalies or death. As previously shown, women with placenta previa have significantly more maternal morbidities. CONCLUSION: Increased maternal morbidity was noted; however, only those neonatal morbidities associated with preterm delivery occurred in the placenta previa group.

Nonclinical parameters affecting primary cesarean rates in the United States.

OBJECTIVE: Cesarean is the single most common operation in United States and has reached epidemic proportions in recent decades. Our objective was to study the effect of nonclinical parameters on primary cesarean rates in a large contemporary population. STUDY DESIGN: We designed a retrospective multicenter study using data obtained from electronic medical records from 19 U.S. hospitals between 2005 and 2007 (Consortium on Safe Labor Database), which included 145,764 term, singleton, nonanomalous, vertex, live births that included labor. The impact of nonclinical parameters (patient and provider characteristics, time of delivery, institutional policies, and insurance type) was investigated using modified Poisson regression methodology and classification and regression tree analysis. RESULTS: There were 125,517 vaginal and 20,247 cesarean deliveries. Using the multivariable model, the nonclinical parameters with statistical significance for primary cesarean were delivery during evening hours, a male provider, public insurance, and nonwhite race (p < 0.001). CONCLUSIONS: Cesarean rates are associated with several nonclinical factors. Further investigation into these factors might help to develop strategies to reduce their influence and hence the rates of cesarean.

Labor patterns in twin gestations.

OBJECTIVE: To compare labor progression in twin vs singleton gestations. STUDY DESIGN: Retrospective review of electronic database created by Consortium on Safe Labor, reflecting labor and delivery information from 12 clinical centers 2002-2008. Women with twin gestations, cephalic presentation of presenting twin, gestational age ≥34 weeks, with ≥2 cervical examinations were included. Exclusion criteria were fetal anomalies or demise. Singleton controls were selected by the same criteria. Categorical variables were analyzed by χ(2); continuous by Student t test. Interval censored regression was used to determine distribution for time of cervical dilation in centimeters, or "traverse times," and controlled for confounding factors. Repeated-measures analysis constructed mean labor curves by parity and number of fetuses. RESULTS: A total of 891 twin gestations were compared with 100,513 singleton controls. Twin gestations were more often older, white or African American, earlier gestational age, increased prepregnancy body mass index, and with lower birthweight. There was no difference in number of prior cesarean deliveries, induction, or augmentation, or epidural use. Median traverse times increased at every centimeter interval in nulliparous twins, in both unadjusted and adjusted analysis (P < .01). A similar pattern was noted for multiparas in both analyses. Labor curves demonstrated a delayed inflection point in the labor pattern for nulliparous and multiparous twin gestations. CONCLUSION: Both nulliparous and multiparous women have slower progression of active phase labor with twins even when controlling for confounding factors.

Gestational weight gain and obesity: is 20 pounds too much?

OBJECTIVE: To compare maternal and neonatal outcomes in obese women according to weight change and obesity class. STUDY DESIGN: Cohort study from the Consortium on Safe Labor of 20,950 obese women with a singleton, term live birth from 2002-2008. Risk for adverse outcomes was calculated by multiple logistic regression analysis for weight change categories (weight loss [<0 kg], low [0-4.9 kg], normal [5.0-9.0 kg], high weight gain [>9.0 kg]) in each obesity class (I 30.0-34.9 kg/m(2), II 35.0-39.9 kg/m(2), and III ≥40 kg/m(2)) and by predicted probabilities with weight change as a continuous variable. RESULTS: Weight loss was associated with decreased cesareans for class I women (nulliparas odds ratio [OR], 0.21; 95% confidence interval [CI], 0.11-0.42; multiparas OR, 0.61; 95% CI, 0.45-0.83) and increased small for gestational age infants (class I OR, 1.8; 95% CI, 1.3-2.5; class II OR, 2.2; 95% CI, 1.5-3.2; class III OR, 1.7; 95% CI, 1.1-2.6). High weight gain was associated with increased large for gestational age infants (class I OR, 2.4; 95% CI, 1.9-2.9; class II OR, 1.7; 95% CI, 1.3-2.1; class III OR, 1.6; 95% CI, 1.3-2.1). As weight change increased, the predicted probability for cesareans and large for gestational age infants increased. The predicted probability of low birthweight never exceeded 4% for all obesity classes, but small for gestational age infants increased with decreased weight change. The lowest average predicted probability of adverse outcomes (cesarean, postpartum hemorrhage, small for gestational age, large for gestational age, neonatal care unit admission) occurred when women (class I, II, III) lost weight. CONCLUSION: Optimal maternal and neonatal outcomes appear to occur when weight gain is less than current Institute of Medicine recommendations for obese women. Further study of long-term outcomes is needed with respect to gestational weight changes.

Ambulatory arrhythmia monitoring in pregnant patients with palpitations.

UNLABELLED: OBJECTIVE To assess the frequency of rhythm disturbances (RDs) obtained following placement of a Holter monitor or an event loop recorder (ERT) in patients referred to cardiologists. STUDY DESIGN: Ninety-six gravidas were referred to the cardiology clinic for palpitations, syncope, or dizziness and had Holter monitoring or ERT after a baseline electroencephalogram. Arrhythmias were classified by severity. RESULTS: Gestational age at referral was 22.6 weeks ± 8.3 days. Sixty-five patients had ERTs performed, and 19 had Holter monitors. Seventy-six percent had benign arrhythmias. In our ERT cohort, history of arrhythmias showed a fourfold increase in serious RD during gestation (odds ratio [OR] 4.7, 95% confidence interval [CI] 1.1 to 20.3, p = 0.01); obesity (body mass index > 30) had a fourfold increased risk (OR 4.0, 95% CI 1.0 to 1, p = 0.03). Serious RD did not result in greater chance of cesarean delivery or induction of labor, or a newborn with arrhythmias. CONCLUSION: Most pregnant women with palpitations have benign arrhythmias. ERT appears to be a better method of diagnosis in pregnant women.

What is the optimal time for delivery in women with gestational hypertension?

OBJECTIVE: To assess the optimal timing of delivery for women with gestational hypertension. STUDY DESIGN: A multicenter database that contained 228,668 deliveries was used to extract data on gravidas with gestational hypertension. The week-specific rates of maternal and neonatal morbidity/mortality were calculated after induction of labor. Point wise 95% confidence intervals were calculated around each of these gestational age-specific rates. RESULTS: After induction of labor, the rate of maternal morbidity/mortality reached a nadir of 89.9 per 1000 live births (95% confidence interval, 68.1-111.8) at 38-38 6/7 weeks' gestation, although the rate of neonatal morbidity/mortality fell to 10.5 per 1000 live births (95% confidence interval, 2.8-18.2) at 39-39 6/7 weeks. There were only 3 total stillbirths in our study cohort. CONCLUSION: In women with gestational hypertension, induction of labor between 38- and 39-weeks' balances the lowest maternal and neonatal morbidity/mortality.

Morbidity associated with the use of Foley balloon for cervical ripening in women with prior cesarean delivery.

OBJECTIVE: We evaluated the morbidity of Foley balloon for cervical ripening in comparison to oxytocin alone in women with a prior cesarean delivery. STUDY DESIGN: A four-hospital retrospective review of all women with viable singleton pregnancies and history of a single prior cesarean delivery presenting for cervical ripening between 1994 and 2015. Exposure groups were either Foley balloon or oxytocin, at the treating physician's discretion. The primary outcome was defined as maternal morbidity, evaluated by a composite that included hemorrhage, and/or uterine infection, and/or uterine rupture. We defined two secondary outcomes: neonatal morbidity, and vaginal delivery rate. Neonatal morbidity was evaluated by a composite that included five-minute APGAR score <7 and/or NICU admission. We adjusted results for potential confounding variables, including hospital site, maternal age and race, initial cervical dilation, and gestational age at delivery. RESULTS: We identified 688 patients who received ripening, 276 by Foley balloon and 412 by oxytocin. There was no significant difference in the primary outcome of maternal morbidity between groups: 38 (13.8%) in the Foley balloon group and 79 (19.2%) in the oxytocin group (aOR 1.43; 95% CI, 0.90-2.27). There was no significant difference in the secondary outcome of neonatal morbidity: 31 (11.3%) in the Foley balloon group and 51 (12.4%) in the oxytocin group (aOR 1.02; 95% CI, 0.57-1.80). The rate of vaginal delivery was significantly less in the Foley balloon group compared to the oxytocin group: 56.2% vs 64.1%, p = .037. CONCLUSION: When cervical ripening with either Foley balloon or oxytocin was utilized at the physician's discretion in women with prior cesarean, there was no identified difference in maternal and neonatal morbidity, but the rate of successful vaginal delivery was lower.

Obstetrical and perinatal outcomes among women with gestational hypertension, mild preeclampsia, and mild chronic hypertension.

OBJECTIVE: The purpose of this study was to compare maternal and neonatal outcomes of women with gestational hypertension (GHTN), mild chronic hypertension (CHTN), and mild preeclampsia at delivery. STUDY DESIGN: A multicenter database that contained 228,668 deliveries was used to extract data on gravid women with GHTN, preeclampsia, and CHTN and on women without hypertensive disease (control group). Univariate and multivariate logistic regression analyses were performed. RESULTS: There were 4918 women with GHTN, 5274 women with preeclampsia, 2531 women with CHTN, and 15,221 control subjects. Women with GHTN had the greatest risk for blood transfusion (adjusted odds ratio [aOR], 4.6; 95% confidence interval [CI], 3.4-6.3), intensive care unit admission (aOR, 25.7; 95% CI, 9.8-67.3), and lowest risk for stillbirth (aOR, 0.1; 95% CI, 0.04-0.4); women with preeclampsia had the greatest risk for postpartum hypertension (aOR, 9.6; 95% CI, 7.2-12.9). Neonates with GHTN had the greatest risk for ventilator requirements (aOR, 7.5; 95% CI, 4.6-12.4). CONCLUSION: Women with gestational hypertension and their neonates had significant risks for morbidity, compared with women with mild chronic hypertension and those with mild preeclampsia.

Contemporary labor patterns: the impact of maternal body mass index.

OBJECTIVE: We sought to compare labor patterns by body mass index (BMI). STUDY DESIGN: A total of 118,978 gravidas with a singleton term cephalic gestation were studied. Repeated-measures analysis constructed mean labor curves by parity and BMI categories for those who reached 10 cm. Interval-censored regression analysis determined median traverse times, adjusting for covariates in vaginal deliveries and intrapartum cesareans. RESULTS: In the labor curves, the time difference to reach 10 cm was 1.2 hours from the lowest to highest BMI category for nulliparas. Multiparas entered active phase by 6 cm, but reaching this point took longer for BMI ≥40.0 (3.4 hours) compared to BMI <25.0 (2.4 hours). Progression by centimeter (P < .001 for nulliparas) and from 4-10 cm (P < .001 for nulliparas and multiparas) increased as BMI increased. Second stage length, with and without an epidural, was similar among BMI categories for nulliparas (P > .05) but decreased as BMI increased for multiparas (P < .001). CONCLUSION: Labor proceeds more slowly as BMI increases, suggesting that labor management be altered to allow longer time for these differences.

Assessing preventability for obstetric hemorrhage.

We sought to determine preventability for cases of obstetric hemorrhage, identify preventable factors, and compare differences between levels of hospital. We retrospectively reviewed a 1-year cohort of severe and near-miss obstetric hemorrhage in an urban perinatal network. An expert panel, using a validated preventability model, reviewed all cases. Preventability and distribution of preventability factors were compared between levels of hospital care. Sixty-three severe and near-miss obstetric hemorrhage cases were identified from 11 hospitals; 54% were deemed potentially preventable. Overall preventability was not statistically different by level of hospital, and 88% were provider related. The only treatment-related preventability factors were significantly different between levels of hospital and significantly less common in level III hospitals (p < 0.01). The majority of obstetric hemorrhage was preventable. The most common potentially preventable factor was provider treatment error, and this was significantly more common in level II hospitals. New interventions should be focused on decreasing providers' treatment errors.

Betamethasone in pregnancy: influence of maternal body weight and multiple gestation on pharmacokinetics.

OBJECTIVE: The goals of the study were to estimate the pharmacokinetic parameters of standard dose betamethasone in a large obstetrics population and evaluate the effect of maternal body size and multiple gestation on the pharmacokinetic parameters and their observed variability. STUDY DESIGN: This was a prospective pharmacokinetic study. Liquid chromatography mass spectrometry was used to measure betamethasone plasma concentrations. Pharmacokinetic parameters and significant clinical covariates were estimated with mixed effect modeling. Bootstrap analysis confirmed validity of the model. RESULTS: Two hundred seventy-four blood samples from 77 patients were obtained. The greatest effect on pharmacokinetic variability was observed with maternal lean body weight (LBW). The relationship between the pharmacokinetic parameters and LBW remained linear over a wide range of maternal body sizes. Multiple gestations did not affect the pharmacokinetic parameters. CONCLUSION: Individualization of betamethasone dosing by maternal LBW reduces variability in drug exposure. Mutiple gestations do not require betamethasone dosing adjustment, because pharmacokinetics are the same as singleton gestations.

Effects of magnesium on central arterial compliance in preeclampsia.

OBJECTIVE: The objective of the study was to investigate the effect of MgSO4 infusion on central arterial compliance, using radial artery applanation tonometry in women with preeclampsia. STUDY DESIGN: Seventy women with preeclampsia were prospectively recruited. Radial pulse waveforms were obtained and the aortic waveforms constructed. The arterial compliance surrogates, augmentation pressure (AP) and augmentation index (AIx-75), were derived from the aortic waveform and then compared: prior to MgSO4 (t1), 1 hour after MgSO4 bolus (t2), 4 hours after MgSO4 infusion (t3), and 24 hours after MgSO4 cessation (t4). Statistical analysis was performed using differences of least squared means with Tukey Kramer adjustments. RESULTS: The AP and AIx-75 at t2-t4 were significantly lower compared with t1, with the greatest decrease in arterial stiffness at t3 (P<.05). CONCLUSION: In preeclampsia, MgSO4 improved central arterial compliance. This effect was most exaggerated after 4 hours of infusion and remained 24 hours following MgSO4 completion, suggesting either a sustained arterial compliance effect or resolution of the vasoconstrictive effect of preeclampsia.

Maternal and neonatal outcomes by labor onset type and gestational age.

OBJECTIVE: We sought to determine maternal and neonatal outcomes by labor onset type and gestational age. STUDY DESIGN: We used electronic medical records data from 10 US institutions in the Consortium on Safe Labor on 115,528 deliveries from 2002 through 2008. Deliveries were divided by labor onset type (spontaneous, elective induction, indicated induction, unlabored cesarean). Neonatal and maternal outcomes were calculated by labor onset type and gestational age. RESULTS: Neonatal intensive care unit admissions and sepsis improved with each week of gestational age until 39 weeks (P < .001). After adjusting for complications, elective induction of labor was associated with a lower risk of ventilator use (odds ratio [OR], 0.38; 95% confidence interval [CI], 0.28-0.53), sepsis (OR, 0.36; 95% CI, 0.26-0.49), and neonatal intensive care unit admissions (OR, 0.52; 95% CI, 0.48-0.57) compared to spontaneous labor. The relative risk of hysterectomy at term was 3.21 (95% CI, 1.08-9.54) with elective induction, 1.16 (95% CI, 0.24-5.58) with indicated induction, and 6.57 (95% CI, 1.78-24.30) with cesarean without labor compared to spontaneous labor. CONCLUSION: Some neonatal outcomes improved until 39 weeks. Babies born with elective induction are associated with better neonatal outcomes compared to spontaneous labor. Elective induction may be associated with an increased hysterectomy risk.

Contemporary cesarean delivery practice in the United States.

OBJECTIVE: To describe contemporary cesarean delivery practice in the United States. STUDY DESIGN: Consortium on Safe Labor collected detailed labor and delivery information from 228,668 electronic medical records from 19 hospitals across the United States, 2002-2008. RESULTS: The overall cesarean delivery rate was 30.5%. The 31.2% of nulliparous women were delivered by cesarean section. Prelabor repeat cesarean delivery due to a previous uterine scar contributed 30.9% of all cesarean sections. The 28.8% of women with a uterine scar had a trial of labor and the success rate was 57.1%. The 43.8% women attempting vaginal delivery had induction. Half of cesarean for dystocia in induced labor were performed before 6 cm of cervical dilation. CONCLUSION: To decrease cesarean delivery rate in the United States, reducing primary cesarean delivery is the key. Increasing vaginal birth after previous cesarean rate is urgently needed. Cesarean section for dystocia should be avoided before the active phase is established, particularly in nulliparous women and in induced labor.

Respiratory morbidity in late preterm births.

CONTEXT: Late preterm births (340/7-366/7 weeks) account for an increasing proportion of prematurity-associated short-term morbidities, particularly respiratory, that require specialized care and prolonged neonatal hospital stays. OBJECTIVE: To assess short-term respiratory morbidity in late preterm births compared with term births in a contemporary cohort of deliveries in the United States. DESIGN, SETTING, AND PARTICIPANTS: Retrospective collection of electronic data from 12 institutions (19 hospitals) across the United States on 233,844 deliveries between 2002 and 2008. Charts were abstracted for all neonates with respiratory compromise admitted to a neonatal intensive care unit (NICU), and late preterm births were compared with term births in regard to resuscitation, respiratory support, and respiratory diagnoses. A multivariate logistic regression analysis compared infants at each gestational week, controlling for factors that influence respiratory outcomes. MAIN OUTCOME MEASURES: Respiratory distress syndrome, transient tachypnea of the newborn, pneumonia, respiratory failure, and standard and oscillatory ventilator support. RESULTS: Of 19,334 late preterm births, 7055 (36.5%) were admitted to a NICU and 2032 had respiratory compromise. Of 165,993 term infants, 11,980 (7.2%) were admitted to a NICU, 1874 with respiratory morbidity. The incidence of respiratory distress syndrome was 10.5% (390/3700) for infants born at 34 weeks' gestation vs 0.3% (140/41,764) at 38 weeks. Similarly, incidence of transient tachypnea of the newborn was 6.4% (n = 236) for those born at 34 weeks vs 0.4% (n = 155) at 38 weeks, pneumonia was 1.5% (n = 55) vs 0.1% (n = 62), and respiratory failure was 1.6% (n = 61) vs 0.2% (n = 63). Standard and oscillatory ventilator support had similar patterns. Odds of respiratory distress syndrome decreased with each advancing week of gestation until 38 weeks compared with 39 to 40 weeks (adjusted odds ratio [OR] at 34 weeks, 40.1; 95% confidence interval [CI], 32.0-50.3 and at 38 weeks, 1.1; 95% CI, 0.9-1.4). At 37 weeks, odds of respiratory distress syndrome were greater than at 39 to 40 weeks (adjusted OR, 3.1; 95% CI, 2.5-3.7), but the odds at 38 weeks did not differ from 39 to 40 weeks. Similar patterns were noted for transient tachypnea of the newborn (adjusted OR at 34 weeks, 14.7; 95% CI, 11.7-18.4 and at 38 weeks, 1.0; 95% CI, 0.8-1.2), pneumonia (adjusted OR at 34 weeks, 7.6; 95% CI, 5.2-11.2 and at 38 weeks, 0.9; 95% CI, 0.6-1.2), and respiratory failure (adjusted OR at 34 weeks, 10.5; 95% CI, 6.9-16.1 and at 38 weeks, 1.4; 95% CI, 1.0-1.9). CONCLUSION: In a contemporary cohort, late preterm birth, compared with term delivery, was associated with increased risk of respiratory distress syndrome and other respiratory morbidity.