Heather Frey

The epidemiology, etiology, and costs of preterm birth

After decades of rising preterm birth rates in the USA and other countries, recent prematurity rates seem to be on the decline. Despite this optimistic trend, preterm birth rates remain higher in the USA, where nearly one in every eight infants is born early, compared to other developed countries. The prevention of preterm birth is considered a public health priority because of the potential to reduce infant and childhood morbidity and mortality related to this condition. Unfortunately, progress has been modest. One of the greatest challenges in studying this outcome is that preterm birth is a complex condition resulting from multiple etiologic pathways. Recently, experts have developed innovative frameworks for classifying and studying preterm birth based on phenotype. These proposed classification systems have only recently been adopted, but a different perspective on a longstanding problem has the potential to lead to new discoveries.

Loop Electrosurgical Excision Procedure and Risk of Preterm Birth: A Systematic Review and Meta-analysis

OBJECTIVE: To assess whether loop electrosurgical excision procedure (LEEP) increases the risk for preterm birth before 37 weeks of gestation and clarify whether the increased risk for preterm birth is attributable to the procedure itself or to risk factors associated with cervical dysplasia. DATA SOURCES: Two authors performed a search of the relevant data through February 2013 using PubMed, Embase, Scopus, CENTRAL, and ClinicalTrials.gov. METHODS OF STUDY SELECTION: We included observational studies that compared rates of preterm birth in women with prior LEEP with women with no history of cervical excision. Nineteen of 559 identified studies met selection criteria. TABULATION, INTEGRATION, AND RESULTS: We compared women with a history of LEEP with two unexposed groups without a history of cervical excision: 1) women with an unknown or no history of cervical dysplasia; and 2) women with a history of cervical dysplasia but no cervical excision. The primary outcome was preterm birth before 37 weeks of gestation. Secondary outcomes were preterm birth before 34 weeks of gestation, spontaneous preterm birth, preterm premature rupture of membranes, and perinatal mortality. DerSimonian-Laird random effects models were used. We assessed heterogeneity between studies using the Q and I2 tests. Stratified analyses and metaregression were performed to assess confounding. Nineteen studies were included with a total of 6,589 patients with a history of LEEP and 1,415,015 without. Overall, LEEP was associated with an increased risk of preterm birth before 37 weeks of gestation (pooled relative risk 1.61, 95% confidence interval [CI] 1.35–1.92). However, no increased risk was found when women with a history of LEEP were compared with women with a history cervical dysplasia but no cervical excision (pooled relative risk 1.08, 95% CI 0.88–1.33). CONCLUSION: Women with a history of LEEP have similar risk of preterm birth when compared with women with prior dysplasia but no cervical excision. Common risk factors for both preterm birth and dysplasia likely explain findings of association between LEEP and preterm birth, but LEEP itself may not be an independent risk factor for preterm birth.

Immediate compared with delayed pushing in the second stage of labor: a systematic review and meta-analysis.

OBJECTIVE: To estimate whether immediate or delayed pushing in the second stage of labor optimizes spontaneous vaginal delivery and other perinatal outcomes. DATA SOURCES: We searched electronic databases MEDLINE and CINHAL through August 2011 without restrictions. The search terms used were MeSH headings, text words, and word variations of the words or phrases labor, laboring down, passive descent, passive second stage, physiologic second stage, spontaneous pushing, pushing, or bearing down. METHODS OF STUDY SELECTION: We searched for randomized controlled trials comparing immediate with delayed pushing in the second stage of labor. The primary outcome was spontaneous vaginal delivery. Secondary outcomes were instrumental delivery, cesarean delivery, duration of the second stage, duration of active pushing, and other maternal and neonatal outcomes. Heterogeneity was assessed using the Q test and I2. Pooled relative risks (RRs) and weighted mean differences were calculated using random-effects models. TABULATION, INTEGRATION, AND RESULTS: Twelve randomized controlled trials (1,584 immediate and 1,531 delayed pushing) met inclusion criteria. Overall, delayed pushing was associated with an increased rate of spontaneous vaginal delivery compared with immediate pushing (61.5% compared with 56.9%, pooled RR 1.09, 95% confidence interval [CI] 1.03–1.15). This increase was smaller and not statistically significant among high-quality studies (59.0% compared with 54.9%, pooled RR 1.07, 95% CI 0.98–1.26) but larger and statistically significant in lower-quality studies (81.0% compared with 71.0%%, pooled RR 1.13, 95% CI 1.02–1.24). Operative vaginal delivery rates were high in most studies and not significantly different between the two groups (33.7% compared with 37.4%, pooled RR 0.89, 95% CI 0.76–1.06). Delayed pushing was associated with prolongation of the second stage (weighted mean difference 56.92 minutes, 95% CI 42.19–71.64) and shortened duration of active pushing (weighted mean difference −21.98 minutes, 95% CI −31.29 to −12.68). CONCLUSION: Studies to date suggest there are few clinical differences in outcomes with immediate compared with delayed pushing in the second stage of labor, especially when high-quality studies are pooled. Effects on maternal and neonatal outcomes remain uncertain.

Stillbirth risk among fetuses with ultrasound-detected isolated congenital anomalies.

OBJECTIVE: To estimate the risk of stillbirth among pregnancies complicated by a major isolated congenital anomaly detected by antenatal ultrasonography and the influence of incidental growth restriction. METHODS: A retrospective cohort study of all consecutive singleton pregnancies undergoing routine anatomic survey between 1990 and 2009 was performed. Stillbirth rates among fetuses with an ultrasound-detected isolated major congenital anomaly were compared with fetuses without major anomalies. Stillbirth rates were calculated per 1,000 ongoing pregnancies. Exclusion criteria included delivery before 24 weeks of gestation, multiple fetal anomalies, minor anomalies, and chromosomal abnormalities. Analyses were stratified by gestational age at delivery (before 32 weeks compared with 32 weeks of gestation or after) and birth weight less than the 10th percentile. We adjusted for confounders using logistic regression. RESULTS: Among 65,308 singleton pregnancies delivered at 24 weeks of gestation or after, 873 pregnancies with an isolated major congenital anomaly (1.3%) were identified. The overall stillbirth rate among fetuses with a major anomaly was 55 per 1,000 compared with 4 per 1,000 in nonanomalous fetuses (adjusted odds ratio [OR] 15.17, 95% confidence interval [CI] 11.03–20.86). Stillbirth risk in anomalous fetuses was similar before 32 weeks of gestation (26/1,000) and 32 weeks of gestation or after (31/1,000). Among growth-restricted fetuses, the stillbirth rate increased among anomalous (127/1,000) and nonanomalous fetuses (18/1,000), and congenital anomalies remained associated with higher rates of stillbirth (adjusted OR 8.20, 95% CI 5.27–12.74). CONCLUSION: The stillbirth rate is increased in anomalous fetuses regardless of incidental growth restriction. These risks can assist practitioners in designing care plans for anomalous fetuses who have elevated and competing risks of stillbirth and neonatal death. LEVEL OF EVIDENCE: II

Factors associated with higher oxytocin requirements in labor.

Abstract Objective: To identify clinical characteristics associated with high maximum oxytocin doses in women who achieve complete cervical dilation. Methods: A retrospective nested case-control study was performed within a cohort of all term women at a single center between 2004 and 2008 who reached the second stage of labor. Cases were defined as women who had a maximum oxytocin dose during labor >20 mu/min, while women in the control group had a maximum oxytocin dose during labor of ≤20 mu/min. Exclusion criteria included no oxytocin administration during labor, multiple gestations, major fetal anomalies, nonvertex presentation, and prior cesarean delivery. Multiple maternal, fetal, and labor factors were evaluated with univariable analysis and multivariable logistic regression. Results: Maximum oxytocin doses >20 mu/min were administered to 108 women (3.6%), while 2864 women received doses ≤20 mu/min. Factors associated with higher maximum oxytocin dose after adjusting for relevant confounders included maternal diabetes, birthweight >4000 g, intrapartum fever, administration of magnesium, and induction of labor. Conclusions: Few women who achieve complete cervical dilation require high doses of oxytocin. We identified maternal, fetal and labor factors that characterize this group of parturients.

Risk of cesarean delivery after loop electrosurgical excision procedure

OBJECTIVE: To estimate whether previous loop electrosurgical excision procedure (LEEP) affects the risk of cesarean delivery. METHODS: A secondary analysis of a multicenter retrospective cohort study was performed. Women who underwent a prior LEEP were compared with two unexposed cohorts: 1) women with prior screening cervical cytology only; and 2) women with prior cervical punch biopsy. The pregnancy evaluated in this analysis was the first pregnancy of a duration more than 20 weeks of gestation after the identifying cervical procedure. Stratified and multivariable logistic regression analyses were used to control for confounding. RESULTS: Five hundred ninety-eight women with prior LEEP, 588 women with screening cytology only, and 552 women with cervical biopsy were included in this study. After adjusting for relevant confounders, similar rates of cesarean delivery were seen in women with prior LEEP (31.6%) and women with prior cervical cytology only (29.3%, adjusted odds ratio [OR] 1.06, 95% confidence interval [CI] 0.79–1.41). Likewise, no differences were found in rates of cesarean delivery when women with prior LEEP were compared with those with a prior punch biopsy (29.0%, adjusted OR 0.99, 95% CI 0.74–1.33). Among women who had a cesarean delivery, arrest of labor was the indication for cesarean delivery in a similar proportion of women in the groups (LEEP compared with cytology only, P=.12; LEEP compared with biopsy, P=.50). Loop electrosurgical excision procedure specimen size did not vary by delivery mode. Length of time between LEEP and subsequent pregnancy also did not influence delivery mode. CONCLUSION: Loop electrosurgical excision procedure does not affect mode of delivery in the subsequent pregnancy. LEVEL OF EVIDENCE: II

Optimal Admission Cervical Dilation in Spontaneously Laboring Women.

OBJECTIVE To estimate the impact of admission cervical dilation on the risk of cesarean in spontaneously laboring women at term. STUDY DESIGN Secondary analysis of a prospective cohort study of women admitted in term labor with a singleton gestation. Women with rupture of membranes before admission, induction of labor, or prelabor cesarean were excluded. The association between cesarean and cervical dilation at admission was estimated, and results were stratified by parity. Relative risks (RRs) and 95% confidence intervals (CIs) were calculated, using cervical dilation ≥ 6 cm as the reference group. Cesarean for arrest was secondarily explored. RESULTS A total of 2,033 spontaneously laboring women met inclusion criteria. Women admitted at <6 cm dilation had an increased risk of cesarean compared with those admitted at ≥6 cm (13.2 vs. 3.5%; RR 3.73; 95% CI 1.94-7.17). The increased risk was noted in nulliparous (16.8 vs. 7.1%; RR 2.35; 95% CI 0.90-6.13) and multiparous (11.0 vs. 2.5%; RR 4.36; 95% CI 1.80-10.52) women, but was statistically significant only in multiparous women. CONCLUSIONS Decreasing cervical dilation at admission, particularly <6 cm, is a modifiable risk factor for cesarean, especially in multiparous women. This should be considered in the decision-making process about timing of admission in term labor.

Interpreting category II fetal heart rate tracings: does meconium matter?

OBJECTIVE Category II fetal heart rate (FHR) tracings are considered indeterminate; thus, improved risk stratification of category II FHR tracings is needed. We estimated whether the presence of meconium increased the risk of adverse neonatal outcomes. STUDY DESIGN This study was conducted within a prospective cohort of 5000 women with singleton pregnancies who were admitted in labor at term. Pregnancies with category II FHR in the 60 minutes before delivery were included. FHR data were extracted by trained nurses who were blinded to clinical outcome. The exposure was the presence of meconium. The primary outcome was a composite neonatal morbidity defined as ≥1 of the following: neonatal death, neurologic morbidity, respiratory morbidity, hypotension that required treatment, and sepsis. Secondary outcomes were nursery admission, cord pH, 5-minute Apgar score, and components of the composite. Logistic regression was used to adjust for confounders. RESULTS Of the 3257 women with category II FHR tracings, 693 women (21.3%) had meconium, and 2564 women (78.7%) did not. Meconium was associated with higher risk of the composite morbidity (adjusted odds ratio, 2.49; 95% confidence interval, 1.78-3.48) and increased risks of the secondary outcomes. The associations remained significant when infants with meconium aspiration syndrome were excluded. Thick meconium was associated significantly with the composite morbidity. CONCLUSION The presence of meconium is associated with an increased risk of neonatal morbidity in women with category II FHR pattern. This clinical factor may assist clinicians in managing category II FHR patterns in labor.

Medical and nonmedical factors influencing utilization of delayed pushing in the second stage.

OBJECTIVE To evaluate factors impacting selection to delayed pushing in the second stage of labor. STUDY DESIGN This case-control study was a secondary analysis of a large retrospective cohort study. Cases included women who delayed pushing for 60 minutes or more in the second stage of labor. Controls began pushing prior to 60 minutes from the time of diagnosis of complete dilation. Demographic, labor, and nonmedical factors were compared among cases and controls. Logistic regression modeling was used to identify factors independently associated with delayed pushing. RESULTS We identified 471 women who delayed pushing and 4819 controls. Nulliparity, maternal body mass index > 25, high fetal station at complete dilation, regional anesthesia use, and start of second stage during staffing shift change were independent factors associated with increased use of delayed pushing. On the other hand, black race and second-stage management during night shift were associated with lower odds of employing delayed pushing. Delayed pushing was more commonly employed in nulliparous women, but 38.9% of multiparous women also delayed pushing. CONCLUSION We identified multiple factors associated with use of delayed pushing. This study helps to define current patterns of second-stage labor management.

Can contraction patterns predict neonatal outcomes

Abstract Objective: To estimate the association between contraction patterns in labor and neonatal outcomes. Methods: A nested case–control study within a consecutive term birth cohort included women in labor with intrauterine pressure catheters (IUPCs) who reached the second stage. Cases were women delivering neonates with composite morbidity: special care or intensive care unit admission, umbilical artery pH ≤ 7.1 or 5-min Apgar < 7. The control group delivered without any components of the composite morbidity. Contraction frequency, duration, relaxation time, Montevideo units (MVUs) and baseline tone in the last 30 min prior to delivery were compared. We used logistic regression to adjust for potential confounders and receiver operating characteristic curves to evaluate the ability of contraction parameters to predict adverse neonatal outcomes. Results: There were 183 cases of adverse neonatal outcomes and 2172 controls without the composite outcome. Contraction duration, relaxation time, MVUs and baseline tone did not significantly differ between the groups. Tachysystole was more common in women with the adverse neonatal outcome (21% versus 15%, p = 0.01). A model including tachysystole, oxytocin use and nulliparity did not adequately predict the adverse outcome (AUC = 0.61). Conclusions: Although tachysystole is associated with adverse neonatal outcomes, uterine activity cannot be used to predict neonatal outcome.