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Objective:  Error in birthweight prediction by sonographic estimated fetal weight (EFW) has clinical implications, such as avoidable cesarean or misclassification of fetal risk in labor. We aimed to evaluate optimal timing of ultrasound and which fetal measurements contribute to error in fetal ultrasound estimations of birth size at the extremes of birthweight., Study Design:  We compared differences in head circumference (HC), abdominal circumference (AC), femur length, and EFW between ultrasound and corresponding birth measurements within 14 ( n  = 1,290) and 7 ( n  = 617) days of birth for small- (SGA, <10th percentile), appropriate- (AGA, 10th-90th), and large-for-gestational age (LGA, >90th) newborns., Results:  Average differences between EFW and birthweight for SGA neonates were: -40.2 g (confidence interval [CI]: -82.1, 1.6) at 14 days versus 13.6 g (CI: -52.4, 79.7) at 7 days; for AGA, -122.4 g (-139.6, -105.1) at 14 days versus -27.2 g (-50.4, -4.0) at 7 days; and for LGA, -242.8 g (-306.5, -179.1) at 14 days versus -72.1 g (-152.0, 7.9) at 7 days. Differences between fetal and neonatal HC were larger at 14 versus 7 days, and similar to patterns for EFW and birthweight, differences were the largest for LGA at both intervals. In contrast, differences between fetal and neonatal AC were larger at 7 versus 14 days, suggesting larger error in AC estimation closer to birth., Conclusion:  Using a standardized ultrasound protocol, SGA neonates had ultrasound measurements closer to actual birth measurements compared with AGA or LGA neonates. LGA neonates had the largest differences between fetal and neonatal size, with measurements 14 days from delivery showing 3- to 4-fold greater differences from birthweight. Differences in EFW and birthweight may not be explained by a single fetal measurement; whether estimation may be improved by incorporation of other knowable factors should be evaluated in future research., Key Points: · Ultrasound measurements may be inadequate to predict neonatal size at birth.. · Birthweight estimation error is higher for neonates >90th percentile.. · There is higher error in AC closer to birth.., Competing Interests: None declared., (Thieme. All rights reserved.)

Objective:  This study aimed to examine associations of fetal biometric and amniotic fluid measures with intrapartum primary cesarean delivery (PCD) and develop prediction models for PCD based on ultrasound parameters and maternal factors., Study Design:  Secondary analysis of the National Institute of the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) Fetal Growth Studies-singleton cohort (2009-2013) including patients with uncomplicated pregnancies and intent to deliver vaginally at ≥37 0/7 weeks. The estimated fetal weight, individual biometric parameters, fetal asymmetry measurements, and amniotic fluid single deepest vertical pocket assessed at the final scan (mean 37.5 ± 1.9 weeks) were categorized as <10th, 10th to 90th (reference), and >90th percentiles. Logistic regression analyses examined the association between the ultrasound measures and PCD. Fetal and maternal SuperLearner prediction algorithms were constructed for the full and nulliparous cohorts., Results:  Of the 1,668 patients analyzed, 249 (14.9%) had PCD. The fetal head circumference, occipital-frontal diameter, and transverse abdominal diameter >90th percentile (adjusted odds ratio [aOR] = 2.50, 95% confidence interval [95% CI]: 1.39, 4.51; aOR = 1.86, 95% CI: 1.02, 3.40; and aOR = 2.13, 95% CI: 1.16, 3.89, respectively) were associated with PCD. The fetal model demonstrated poor ability to predict PCD in the full cohort and in nulliparous patients (area under the receiver-operating characteristic curve [AUC] = 0.56, 95% CI: 0.52, 0.61; and AUC = 0.54, 95% CI: 0.49, 0.60, respectively). Conversely, the maternal model had better predictive capability overall (AUC = 0.79, 95% CI: 0.75, 0.82) and in the nulliparous subgroup (AUC = 0.72, 95% CI: 0.67, 0.77). Models combining maternal/fetal factors performed similarly to the maternal model (AUC = 0.78, 95% CI: 0.75, 0.82 in full cohort, and AUC = 0.71, 95% CI: 0.66, 0.76 in nulliparas)., Conclusion:  Although a few fetal biometric parameters were associated with PCD, the fetal prediction model had low performance. In contrast, the maternal model had a fair-to-good ability to predict PCD., Key Points: · Fetal HC >90th percentile was associated with cesarean delivery.. · Fetal parameters did not effectively predict PCD.. · Maternal factors were more predictive of PCD.. · Maternal/fetal and maternal models performed similarly.. · Prediction models had lower performance in nulliparas.., Competing Interests: D.A.W. has been a consultant for Parsagen, for which she received no compensation. The other authors did not report any potential conflict of interest., (Thieme. All rights reserved.)

Objective: This study aimed to investigate asthma medication reduction in the periconceptional period as it relates to asthma status and adverse outcomes in pregnancy., Study Design: In a prospective cohort study, self-reported current and past asthma medications were collected and analyzes compared measures of asthma status in women who discontinued asthma medication in the 6 months prior to enrollment ("step-down") versus those who did not ("no change"). Evaluation of asthma was done at three study visits (one per trimester) and by daily diaries, including measures of lung function (percent predicted forced expiratory volume in 1 and 6 s [%FEV1, %FEV6], peak expiratory flow [%PEF], forced vital capacity [%FVC], FEV1 to FVC ratio [FEV1/FVC]), lung inflammation (fractional exhaled nitric oxide [FeNO], ppb), rate of asthma symptoms (activity limitation, night symptoms, rescue inhaler use, wheeze, shortness of breath, cough, chest tightness, chest pain), and rate of asthma exacerbations. Adverse pregnancy outcomes were also evaluated. Adjusted regression analyses examined whether adverse outcomes differed by periconceptional asthma medication changes., Results: Of 279 participants included in analyses, 135 (48.4%) did not change asthma medication in the periconceptional period, whereas 144 (51.6%) reported a step down in medication. Those in the step-down group were more likely to have milder disease (88 [61.1%] in the step-down vs. 74 [54.8%] in the no change group), exhibited less activity limitation (rate ratio [RR]: 0.68, 95% confidence interval [CI]: 0.47-0.98), and experienced fewer asthma attacks (RR: 0.53, 95% CI: 0.34-0.84) during pregnancy. The step-down group had a nonsignificant increase in overall odds of experiencing an adverse pregnancy outcome (odds ratio: 1.62, 95% CI: 0.97-2.72)., Conclusion: Over half of women with asthma reduce asthma medication in the periconceptional period. Although these women typically have milder disease, a step down in medication may be associated with an increased risk of adverse pregnancy outcomes., Key Points: · Many women reduce their asthma medication in pregnancy.. · Reduction is more common among those with mild disease.. · Medication reduction may lead to adverse pregnancy outcomes.., Competing Interests: None declared., (Thieme. All rights reserved.)

Objective: This study aimed to evaluate fetal biometrics as predictors of shoulder dystocia (SD) in a low-risk obstetrical population., Study Design: Participants were enrolled as part of a U.S.-based prospective cohort study of fetal growth in low-risk singleton gestations ( n  = 2,802). Eligible women had liveborn singletons ≥2,500 g delivered vaginally. Sociodemographic, anthropometric, and pregnancy outcome data were abstracted by research staff. The diagnosis of SD was based on the recorded clinical impression of the delivering physician. Simple logistic regression models were used to examine associations between fetal biometrics and SD. Fetal biometric cut points, selected by Youden's J and clinical determination, were identified to optimize predictive capability. A final model for SD prediction was constructed using backward selection. Our dataset was randomly divided into training (60%) and test (40%) datasets for model building and internal validation., Results: A total of 1,691 women (98.7%) had an uncomplicated vaginal delivery, while 23 (1.3%) experienced SD. There were no differences in sociodemographic or maternal anthropometrics between groups. Epidural anesthesia use was significantly more common (100 vs. 82.4%; p  = 0.03) among women who experienced SD compared with those who did not. Amniotic fluid maximal vertical pocket was also significantly greater among SD cases (5.8 ± 1.7 vs. 5.1 ± 1.5 cm; odds ratio = 1.32 [95% confidence interval: 1.03,1.69]). Several fetal biometric measures were significantly associated with SD when dichotomized based on clinically selected cut-off points. A final prediction model was internally valid with an area under the curve of 0.90 (95% confidence interval: 0.81, 0.99). At a model probability of 1%, sensitivity (71.4%), specificity (77.5%), positive (3.5%), and negative predictive values (99.6%) did not indicate the ability of the model to predict SD in a clinically meaningful way., Conclusion: Other than epidural anesthesia use, neither sociodemographic nor maternal anthropometrics were significantly associated with SD in this low-risk population. Both individually and in combination, fetal biometrics had limited ability to predict SD and lack clinical usefulness., Key Points: · SD unpredictable in low-risk women.. · Fetal biometry does not reliably predict SD.. · Epidural use associated with increased SD risk.. · SD prediction models clinically inefficient.., Competing Interests: D.A.W. has been a consultant for Parsogen, for which she received no compensation., (Thieme. All rights reserved.)

Objective: This study aimed to assess the impact of common asthma medication regimens on asthma symptoms, exacerbations, lung function, and inflammation during pregnancy., Study Design: A total of 311 women with asthma were enrolled in a prospective pregnancy cohort. Asthma medication regimen was categorized into short-acting β agonist (SABA) alone, SABA + inhaled corticosteroid (ICS), SABA + ICS + long-acting β agonist (LABA), and no asthma medications (reference). We evaluated asthma control at enrollment (< 15 weeks' gestation) and its change into trimesters 2 and 3, including per cent predicted forced expiratory volume in 1 second (%FEV1) and peak expiratory flow (%PEF), pulse oximetry, fractional exhaled nitric oxide (FeNO), asthma symptoms (asthma attacks/month, night symptoms/week), and severe exacerbations. Linear mixed models adjusted for site, age, race, annual income, gestational age, body mass index, and smoking, and propensity scores accounted for asthma control status at baseline., Results: Women taking SABA + ICS and SABA + ICS + LABA had better first trimester %PEF (83.5% [75.7-91.3] and 84.6% [76.9-92.3], respectively) compared with women taking no asthma medications (72.7% [66.0-79.3]). Women taking SABA + ICS + LABA also experienced improvements in %FEV1 (+11.1%, p  < 0.01) in the third trimester and FeNO in the second (-12.3 parts per billion [ppb], p  < 0.01) and third (-11.0 ppb, p  < 0.01) trimesters as compared with the trajectory of women taking no medications. SABA + ICS use was associated with increased odds of severe exacerbations in the first (odds ratio [OR]: 2.22 [1.10-4.46]) and second (OR: 3.15 [1.11-8.96]) trimesters, and SABA + ICS + LABA use in the second trimester (OR: 7.89 [2.75-21.47]). Women taking SABA alone were similar to those taking no medication., Conclusion: Pregnant women taking SABA + ICS and SABA + ICS + LABA had better lung function in the first trimester. SABA + ICS + LABA was associated with improvements in lung function and inflammation across gestation. However, both the SABA + ICS and SABA + ICS + LABA groups had a higher risk of severe exacerbation during early to mid-pregnancy., Key Points: · Medication regimens may affect perinatal asthma control.. · Intensive regimens improved lung function/inflammation.. · Women on intensive regimens had more acute asthma events.., Competing Interests: None declared., (Thieme. All rights reserved.)

Objective: The objective of the study was to determine whether adding longitudinal measures of fundal height (FH) to the standard cross-sectional FH to trigger third trimester ultrasound estimated fetal weight (EFW) would improve small for gestational age (SGA) prediction., Study Design: We developed a longitudinal FH calculator in a secondary analysis of a prospective cohort study of 1,939 nonobese pregnant women who underwent serial FH evaluations at 12 U.S. clinical sites. We evaluated cross-sectional FH measurement ≤ -3 cm at visit 3 (mean: 32.0 ± 1.6 weeks) versus the addition of longitudinal FH up to and including visit 3 to trigger an ultrasound to diagnose SGA defined as birth weight <10th percentile. If the FH cut points were not met, the SGA screen was classified as negative. If FH cut points were met and EFW was <10th percentile, the SGA screen was considered positive. If EFW was ≥10th percentile, the SGA screen was also considered negative. Sensitivity, specificity, and positive predictive value (PPV) and negative predictive value (NPV) were computed., Results: In a comparison of methods, 5.8% of women were classified as at risk of SGA by both cross-sectional and longitudinal classification methods; cross-sectional FH identified an additional 4.0%, and longitudinal fundal height identified a separate, additional 4.5%.Using cross-sectional FH as an ultrasound trigger, EFW had a PPV and NPV for SGA of 69 and 92%, respectively. After adding longitudinal FH, PPV increased to 74%, whereas NPV of 92% remained unchanged; however, the number of women who underwent triggered EFW decreased from 9.7 to 5.7%., Conclusion: An innovative approach for calculating longitudinal FH to the standard cross-sectional FH improved identification of SGA birth weight, while simultaneously reducing the number of triggered ultrasounds. As an essentially free-of-charge screening test, our novel method has potential to decrease costs as well as perinatal morbidity and mortality (through better prediction of SGA)., Key Points: · We have developed an innovative calculator for fundal height trajectory.. · Longitudinal fundal height improves detection of SGA.. · As a low cost screening test, the fundal height calculator may decrease costs and morbidity through better prediction of SGA.., Competing Interests: D.A.W. has been a consultant for Parsagen, for which she received no compensation. She was formerly Professor of Obstetrics and Gynecology, Division of Maternal-Fetal Medicine at University of California, Irvine during time of data collection. She is currently Senior Client Partner at Korn Ferry, Los Angeles, California. At the time of manuscript development, S.J.P. was a postdoctoral fellow at NICHD, and she is currently an employee of Pfizer, Inc, Collegeville, PA. The other authors did not report any potential conflicts of interest., (Thieme. All rights reserved.)

Objective: This study aimed to describe the overall quantity and type of supplements and medications used during pregnancy in a low-risk cohort and to examine any racial/ethnic differences in intake., Study Design: We used data from 2,164 racially/ethnically diverse, nonobese, and low-risk pregnant women participating without pre-pregnancy chronic conditions in a prospective cohort study at 12 sites across the United States. Medication data were self-reported as free text in enrollment, follow-up visit questionnaires, and abstracted from medical records at delivery. Supplements and medications data were mapped to their active ingredients and categorized into corresponding classes using the Slone Drug Dictionary. The total number and classes of supplements and medications consumed during pregnancy were calculated. Modified Poisson regression models were used to estimate the racial/ethnic differences in supplements and medications intake. All models were adjusted for maternal sociodemographic factors and study site., Results: 98% of women took at least one supplement during pregnancy, with prenatal vitamins/multivitamins being most common. While only 31% reported taking no medications during pregnancy, 23% took one, 18% took two, and 28% took three or more. The percentage of women taking at least one medication during pregnancy was highest among non-Hispanic white women and lowest among Asians (84 vs. 55%, p  < 0.001). All racial/ethnic groups reported taking the same top four medication classes including central nervous system agents, gastrointestinal drugs, anti-infective agents, and antihistamines. Compared with non-Hispanic white women, Hispanic (adjusted relative risk [aRR]: 0.84, 95% confidence interval [CI]: 0.71-0.98), and Asian women (aRR: 0.83, 95% CI: 0.70-0.98) were less likely to take central nervous system agents, as well as gastrointestinal drugs (Hispanics aRR: 0.79, 95% CI: 0.66-0.94; Asians aRR = 0.75, 95% CI: 0.63-0.90), and antihistamines (Hispanics aRR: 0.65, 95% CI: 0.47-0.92)., Conclusion: Supplement intake was nearly universal. Medication use was also common among this low-risk pregnancy cohort and differed by race/ethnicity., Gov Identifier: NCT00912132., Key Points: · In women without chronic conditions, medication use is common.. · Racial/ethnic differences exist in prenatal medications use.. · Almost all women use supplements during pregnancy.., Competing Interests: D.A.W. has been a consultant for Parsagen for which she received no compensation. The other authors do not report any potential conflicts of interest., (Thieme. All rights reserved.)

Objective: The aim of this study is to model the association between gestational age at birth and early child development through 3 years of age., Study Design: Development of 5,868 children in Upstate KIDS (New York State; 2008-2014) was assessed at 7 time points using the Ages and Stages Questionnaire (ASQ). The ASQ was implemented using gestational age corrected dates of birth at 4, 8, 12, 18, 24, 30, and 36 months. Whether children were eligible for developmental services from the Early Intervention Program was determined through linkage. Gestational age was based on vital records. Statistical models adjusted for covariates including sociodemographic factors, maternal smoking, and plurality., Results: Compared with gestational age of 39 weeks, adjusted odds ratios (aOR) and 95% confidence intervals of failing the ASQ for children delivered at <32, 32-34, 35-36, 37, 38, and 40 weeks of gestational age were 5.32 (3.42-8.28), 2.43 (1.60-3.69), 1.38 (1.00-1.90), 1.37 (0.98-1.90), 1.29 (0.99-1.67), 0.73 (0.55-0.96), and 0.51 (0.32-0.82). Similar risks of being eligible for Early Intervention Program services were observed (aOR: 4.19, 2.10, 1.29, 1.20, 1.01, 1.00 [ref], 0.92, and 0.78 respectively for <32, 32-34, 37, 38, 39 [ref], 40, and 41 weeks)., Conclusion: Gestational age was inversely associated with developmental delays for all gestational ages. Evidence from our study is potentially informative for low-risk deliveries at 39 weeks, but it is notable that deliveries at 40 weeks exhibited further lower risk., Competing Interests: None declared., (Thieme. All rights reserved.)

Objective: We characterized lipid trajectories and investigated lipids and rate of pregnancy lipid change with the risk of pregnancy loss or preterm delivery <37 weeks., Study Design: In a secondary analysis of 337 women with one to two prior losses assigned to placebo in a randomized controlled trial at four centers (2007-2012), cholesterol, low- and high-density lipoprotein cholesterol (HDL-C), and triglycerides were measured up to 6 months prepregnancy (time 0) and pregnancy up to 7 visits. Trajectories were created using linear mixed models. Multivariable logistic regression with adjustment for maternal characteristics and cholesterol was performed., Results: Lipids decreased from prepregnancy to 4 to 5 weeks, followed by an increase, and were biphasic or triphasic depending on the lipid component. Between 4 and 8 weeks, for every 1-unit increase in HDL-C, there was a 22% decreased odds of loss <14 weeks (odds ratio: 0.78; 95% confidence interval: 0.60, 0.99) and 24% decreased odds of loss or preterm delivery 14 to <37 weeks (odds ratio: 0.76; 95% confidence interval: 0.60, 0.96)., Conclusion: There were no associations with other lipid components or other time points. An impaired rise of HDL-C early in pregnancy may signal maladaptation to pregnancy that is associated with pregnancy loss or preterm delivery., Competing Interests: None declared., (Thieme Medical Publishers 333 Seventh Avenue, New York, NY 10001, USA.)

Objective: This article aims to determine if the number of maternal ultrasound scans where the highest thermal (TI) or mechanical (MI) indices recorded during obstetrical ultrasound exceed 1.0 were associated with neonatal anthropometric measurements., Study Design: A prospective cohort of 2,334 nonobese low-risk pregnant women from 12 U.S. clinical sites underwent a total of six ultrasound scans, for which the highest TI and MI values were recorded. Neonatal anthropometric measurements were obtained within 12 to 24 hours of delivery. Multiple linear regression models adjusted for maternal race/ethnicity, body mass index, weight gain, and gestational age were used to examine associations between the number of maternal ultrasounds during gestation with a TI or MI exceeding 1.0 and the mean change in neonatal anthropometry., Results: Ultrasounds with TI or MI >1.0 were not associated with birth weight, neonatal length, nor head, chest, and abdominal circumferences. TI >1.0 was negatively associated with neonatal mid-upper arm and mid-upper thigh circumferences. MI >1.0 was negatively associated with neonatal skinfold measurements of the anterior thigh and triceps, and neonatal circumferences of the mid-upper thigh and umbilicus., Conclusion: Prenatal ultrasound examinations in which TI or MI intermittently exceeded 1.0 did not identify a pattern of alterations of birth size., Competing Interests: None., (Thieme Medical Publishers 333 Seventh Avenue, New York, NY 10001, USA.)

Objective: To examine labor induction by race/ethnicity and factors associated with disparity in induction., Study Design: This is a retrospective cohort study of 143,634 women eligible for induction ≥24 weeks' gestation from 12 clinical centers (2002-2008). Rates of labor induction for each racial/ethnic group were calculated and stratified by gestational age intervals: early preterm (24 0/7 -33 6/7 ), late preterm (34 0/7 -36 6/7 ), and term (37 0/7 -41 6/7 weeks). Multivariable logistic regression examined the association between maternal race/ethnicity and induction controlling for maternal characteristics and pregnancy complications. The primary outcome was rate of induction by race/ethnicity. Inductions that were indicated, non-medically indicated, or without recorded indication were also compared., Results: Non-Hispanic black (NHB) women had the highest percentage rate of induction, 44.6% ( p  < 0.001). After adjustment, all racial/ethnic groups had lower odds of induction compared with non-Hispanic white (NHW) women. At term, NHW women had the highest percentage rate (45.4%) of non-medically indicated or induction with no indication ( p  < 0.001)., Conclusion: Compared with other racial/ethnic groups, NHW women were more likely to undergo non-medically indicated induction at term. As labor induction may avoid the occurrence of stillbirth, whether this finding explains part of the increased risk of stillbirth for NHB women at term merits further research., Competing Interests: None., (Thieme Medical Publishers 333 Seventh Avenue, New York, NY 10001, USA.)

Competing Interests: Conflict of Interest: None.

Objective  Risk factors for placental abruption have changed, but there has not been an updated systematic review investigating outcomes. Methods  We searched PubMed, EMBASE, Web of Science, SCOPUS, and CINAHL for publications from January 1, 2005 through December 31, 2016. We reviewed English-language publications reporting estimated incidence and/or risk factors for maternal, labor, delivery, and perinatal outcomes associated with abruption. We excluded case studies, conference abstracts, and studies that lacked a referent/comparison group or did not clearly characterize placental abruption. Results  A total of 123 studies were included. Abruption was associated with elevated risk of cesarean delivery, postpartum hemorrhage and transfusion, preterm birth, intrauterine growth restriction or low birth weight, perinatal mortality, and cerebral palsy. Additional maternal outcomes included relaparotomy, hysterectomy, sepsis, amniotic fluid embolism, venous thromboembolism, acute kidney injury, and maternal intensive care unit admission. Additional perinatal outcomes included acidosis, encephalopathy, severe respiratory disorders, necrotizing enterocolitis, acute kidney injury, need for resuscitation, chronic lung disease, infant death, and epilepsy. Conclusion  Few studies examined outcomes beyond the initial birth period, but there is evidence that both mother and child are at risk of additional adverse outcomes. There was also considerable variation in, or absence of, the reporting of abruption definitions., Competing Interests: Conflict of Interest: None., (Thieme Medical Publishers 333 Seventh Avenue, New York, NY 10001, USA.)

Objective  To compare perinatal outcomes in women with oligohydramnios and an unfavorable cervix undergoing labor induction with misoprostol to prostaglandin E2. Study Design  We conducted a secondary analysis of women with oligohydramnios undergoing labor induction in the Consortium on Safe Labor study (2002-2008). Oligohydramnios was recorded in the medical chart. We evaluated perinatal outcomes. We limited the analysis to women with an unfavorable cervix defined by simplified Bishop score ≤ 4. Misoprostol was compared with prostaglandin E2. Women could have received oxytocin, underwent mechanical dilation, or had artificial rupture of membranes, but women who underwent induction with both misoprostol and prostaglandin E2 were excluded. We calculated adjusted odds ratios with 95% confidence intervals, controlling for maternal age, maternal body mass index (kg/m 2 ), parity, and mechanical dilation. Results  Among women with oligohydramnios and an unfavorable cervix who underwent induction of labor, 141 (39.4%) received misoprostol and 217 (60.6%) received prostaglandin E2. There were no significant differences in cesarean delivery, chorioamnionitis, postpartum hemorrhage, transfusion, neonatal intensive care unit (NICU) admission, NICU stay > 72 hours, mechanical ventilation, and neonatal sepsis. Conclusion  In women with oligohydramnios and an unfavorable cervix, induction of labor with misoprostol was comparable to prostaglandin E2., Competing Interests: statement The authors report no conflicts of interest. Institutions involved in the Consortium on Safe Labor are named in the Acknowledgments., (Thieme Medical Publishers 333 Seventh Avenue, New York, NY 10001, USA.)

Objective Evidence for optimal timing of delivery for some pregnancy complications at late preterm gestation is limited. The purpose of this study was to identify center variation of indicated late preterm births. Study design We performed an analysis of singleton late preterm and term births from a large U.S. retrospective obstetrical cohort. Births associated with spontaneous preterm labor, major congenital anomalies, chorioamnionitis, and emergency cesarean were excluded. We used modified Poisson fixed effects logistic regression with interaction terms to assess center variation of indicated late preterm births associated with four medical/obstetric comorbidities after adjusting for socio-demographics, comorbidities, and hospital/provider characteristics. Results We identified 150,055 births from 16 hospitals; 9,218 were indicated late preterm births. We found wide variation of indicated late preterm births across hospitals. The extent of center variation was greater for births associated with preterm premature rupture of membranes (risk ratio [RR] across sites: 0.45-3.05), hypertensive disorders of pregnancy (RR across sites: 0.36-1.27), and placenta previa/abruption (RR across sites: 0.48-1.82). We found less center variation for births associated with diabetes (RR across sites: 0.65-1.39). Conclusion Practice variation in the management of indicated late preterm deliveries might be a source of preventable late preterm birth., (Thieme Medical Publishers 333 Seventh Avenue, New York, NY 10001, USA.)