The Fetal Occiput Posterior Position: State of the Science and a New Perspective

Abstract: Background: The fetal occiput posterior position poses challenges in every aspect of intrapartum care—prevention, diagnosis, correction, supportive care, labor management, and delivery. Maternal and newborn outcomes are often worse and both physical and psychological traumas are more common than with fetal occiput anterior positions. The purpose of this paper is to describe nine prevailing concepts that guide labor and birth management with an occiput posterior fetus, and summarize evidence to clarify the state of the science. Methods: A search was conducted of the databases of PubMed and the Cochrane Library. Additional valuable information was obtained from obstetric and midwifery textbooks, books and websites for the public, conversations with maternity care professionals, and years of experience as a doula. Results: Nine prevailing concepts are as follows: (1) prenatal maneuvers rotate the occiput posterior fetus to occiput anterior; (2) it is possible to detect the occiput posterior fetus prenatally; (3) a fetus who is occiput anterior at the onset of labor will remain in that position throughout labor; (4) back pain in labor is a reliable sign of an occiput posterior fetus; (5) the occiput posterior fetus can be identified during labor by digital vaginal examination; (6) an ultrasound scan is a reliable way to detect fetal position; (7) maternal positions facilitate rotation of the occiput posterior fetus; (8) epidural analgesia facilitates rotation; (9) manual rotation of the fetal head to occiput anterior improves the rate of occiput anterior deliveries. Concepts 1, 2, 3, 4, 5, and 8 have little scientific support whereas concepts 6, 7, and 9 are supported by promising evidence. Conclusions: Many current obstetric practices with respect to the occiput posterior position are unsatisfactory, resulting in failure to identify and correct the problem and thus contributing to high surgical delivery rates and traumatic births. The use of ultrasound examination to identify fetal position is a method that is far superior to other methods, and has the potential to improve outcomes. Research studies are needed to examine the efficacy of midwifery methods of identification, and the effect of promising methods to rotate the fetus (simple positional methods and digital or manual rotation). Based on the findings of this review, a practical approach to care is suggested. (BIRTH 37:1 March 2010)     

持续性枕横位和枕后位病例的产程特点及影响

目的探讨持续性枕横位和枕后位的产程特点及对母儿结局的影响。方法回顾性分析64例持续性枕横位和51例持续性枕后位病例的各阶段产程时间、异常产程及产道损伤、产后出血、羊水粪染(Ⅱ°以上)、新生儿Apgar评分(5min评分≤7分)等情况,并与同期100例枕前位病例进行对比分析。结果持续性枕横位和枕后位的异常产程发生率、产道损伤、产后出血率均较对照组明显增加(P<0.05);羊水粪染及新生儿窒息发生率均较对照组明显增加,两组比较差异均有统计学意义(P<0.05)。结论重视对持续性枕横位和枕后位的早期诊断和及时处理对减少母儿并发症有重要意义。     

Maternal Temperature Elevation and Occiput Posterior Position at Birth Among Low‐Risk Women Receiving Epidural Analgesia

Introduction: To evaluate the relationship between maternal temperature elevation and occiput posterior position at birth as well as the association of fetal head position and temperature elevation on method of birth among women receiving epidural analgesia. Methods: We conducted a secondary analysis of data from the Fetal Orientation during Childbirth by Ultrasound Study (FOCUS), which used serial ultrasounds to evaluate the effect of epidural anesthesia on fetal position at birth in low‐risk women. The current analysis was limited to the 1428 study participants who received epidural analgesia. Results: In our population, 47% (n = 669) of women had a maximum intrapartum temperature greater than or equal to 99.6°F (37.6°C). The prevalence of fetal occiput posterior position at admission did not differ between women who later developed temperature elevations (24.4%) and those who did not (23.6%, P= .70). Women who developed an elevated temperature greater than or equal to 99.6°F (37.6°C) had an increased risk of occiput posterior fetal head position at birth regardless of the amount of temperature elevation (odds ratio [OR]= 2.0; 95% confidence interval [CI], 1.5‐2.8); the association persisted after control for potentially confounding factors (adjusted OR = 1.5; 95% CI, 1.1‐2.1). The cesarean birth rate among women with both temperature elevation and occiput posterior position at birth was more than 12 times the rate of women with neither risk factor (adjusted OR = 12.6; 95% CI, 7.5‐21.2). Discussion: Intrapartum temperature elevation among women receiving epidural analgesia, even if only to 99.6°F (37.6°C), is associated with approximately a 2‐fold increase in the occurrence of occiput posterior fetal head position at birth. Additionally, although this observational study cannot establish causal links, our findings suggest that the relationship between epidural‐related intrapartum temperature elevation and occiput posterior position at birth could contribute to an increased cesarean birth rate among women receiving epidural analgesia for pain relief in labor.     

The feasibility and accuracy of ultrasound assessment in the labor room

Objective: Vaginal examination is widely used to assess the progress of labor; however, it is subjective and poorly reproducible. We aim to assess the feasibility and accuracy of transabdominal and transperineal ultrasound compared to vaginal examination in the assessment of labor and its progress.

Methods: Women were recruited as they presented for assessment of labor to a tertiary inner city maternity service. Paired vaginal and ultrasound assessments were performed in 192 women at 24–42 weeks. Fetal head position was assessed by transabdominal ultrasound defined in relation to the occiput position transformed to a 12-hour clock face; fetal head station defined as head-perineum distance by transperineal ultrasound; cervical dilatation by anterior to posterior cervical rim measurement and caput succedaneum by skin-skull distance on transperineal ultrasound.

Results: Fetal head position was recorded in 99.7% (298/299) of US and 51.5% (154/299) on vaginal examination (p?¹). Bland–Altman analysis showed 95% limits of agreement, ?5.31 to 4.84 clock hours. Head station was recorded in 96.3% (308/320) on vaginal examination (VE) and 95.9% (307/320) on US (p?=?.79¹). Head station and head perineum distance were negatively correlated (Spearman’s r?=??.57, p?p?p?p?Conclusions: We describe comprehensive ultrasound assessments in the labor room that could be translated to the assessment of women in labor. Fetal head position is unreliably determined by vaginal examination and agrees poorly with US. Head perineum distance has a moderate correlation with fetal head station in relation to the ischial spines based on vaginal examination. Cervical dilatation is not reliably assessed by ultrasound except at dilatations of less than 4?cm. Caput is readily quantifiable by ultrasound and its presence is associated with lower fetal head station. Transabdominal and transperineal ultrasound is feasible in the labor room with an accuracy that is generally greater than vaginal examinations.     

Influence of persistent occiput posterior position on delivery outcome.

OBJECTIVE: To evaluate the influence of intrapartum persistent occiput posterior position of the fetal head on delivery outcome and anal sphincter injury, with reference to the association with epidural analgesia. METHODS: We conducted a prospective observational study of 246 women with persistent occiput posterior position in labor during a 2-year period, compared with 13,543 contemporaneous vaginal deliveries with occiput anterior position. RESULTS: The incidence of persistent occiput posterior position was significantly greater among primiparas (2.4%) than multiparas (1.3%; P <.001; 95% confidence interval 1.4, 2.4) and was associated with significantly higher incidences of prolonged pregnancy, induction of labor, oxytocin augmentation of labor, epidural use, and prolonged labor. Only 29% of primiparas and 55% of multiparas with persistent occiput posterior position achieved spontaneous vaginal delivery, and the malposition was associated with 12% of all cesarean deliveries performed because of dystocia. Persistent occiput posterior position was also associated with a sevenfold higher incidence of anal sphincter disruption. Despite a high overall incidence of use of epidural analgesia (47% versus 3%), the institutional incidence of persistent occiput posterior position was lower than that reported 25 years ago. CONCLUSION: Persistent occiput posterior position contributed disproportionately to cesarean and instrumental delivery, with fewer than half of the occiput posterior labors ending in spontaneous delivery and the position accounting for 12% of all cesarean deliveries for dystocia. Persistent occiput posterior position leads to a sevenfold increase in the incidence of anal sphincter injury. Use of epidural analgesia was not related to the malposition.     

Diagnosis and intervention for occiput posterior malposition

OBJECTIVES: To evaluate diagnostic methods used to detect occiput posterior and to describe the efficacy of posturing to enhance rotation from occiput posterior to occiput anterior. DATA SOURCES: Keyword search using PubMed, CINAHL, Cochrane Review, and Dissertation Abstracts International. STUDY SELECTION: Studies published from 1996 to 2006 (except one published in 1983) that focused on the use of ultrasonography versus digital vaginal examination to diagnose fetal position and maternal posturing to enhance rotation from occiput posterior to occiput anterior. DATA EXTRACTION: Eight prospective studies regarding malposition diagnosis were reviewed and analyzed for error rates and predictors affecting ability to detect fetal position; five randomized controlled trials were evaluated for effects of various maternal postures on fetal rotation from occiput posterior to occiput anterior. DATA SYNTHESIS: If fetal malposition is accurately diagnosed in early labor, subsequent nursing management can focus on rotation toward occiput anterior position, leading to a safer delivery for mother and baby. CONCLUSIONS: Antepartum ultrasonography is more accurate than digital vaginal examination in diagnosing fetal malposition; however, its efficacy needs to be further explored using randomized controlled trials and cost-benefit analyses before routine use is recommended. Furthermore, Sims' posture on the same side as the fetal spine is recommended during labor to enhance rotation from occiput posterior to occiput anterior.     

胎儿体重对持续性枕后位产程特征和分娩结局影响的分析

目的:探讨胎儿体重对持续性枕后位产程特征和分娩结局的影响.方法:对2005年12月至2009年12月在本院产科住院分娩228例持续性枕后位产妇的临床资料进行回顾性分析,根据新生儿出生体重分为对照组112例(胎儿体重≥2500 g且＜3500 g)和研究组116例(胎儿体重≥3500 g且＜4250 g).并将两组产程特征、母儿结局进行分析比较.结果:两组产妇产程异常(宫口扩张延缓、停滞,胎头下降延缓、停滞)发生率、临床干预(体位矫正、手转胎头)成功率、剖宫产率、母儿并发症(产后出血、产褥病率、胎儿窘迫、新生儿窒息)发生率差异均有统计学意义(P＜0.05).结论:持续性枕后位产程处理中充分考虑胎儿的体重因素,对于胎儿估计体重≥3500 g的枕后位病例应积极临床干预,干预失败应放宽手术指征,以降低母儿并发症发生率.     

Risk factors for forceps delivery in nulliparous patients

OBJECTIVE: To identify risk factors for forceps delivery during first pregnancy. MATERIALS AND METHODS: A retrospective case-control study was carried out in a tertiary maternity ward between January 2001 and December 2003. A total of 582 nulliparous women, with full-term (>37 weeks gestation), singleton, cephalic pregnancies, who delivered by the vaginal route with or without instrumental assistance were evaluated. RESULTS: The strongest risk factors for forceps delivery were birth weight greater than 4000 g (OR: 6.5; 95% CI: 1.6, 26.9), the occiput posterior position of the fetal head (OR: 5.8; 95% CI: 2.5, 13.8), and epidural analgesia (OR: 7.7; 95% CI: 4.1, 14.7). Other significant risk factors for forceps delivery were age over 35 years (OR: 2.4; 95% CI: 1.1, 5.1), induction of labor (OR: 2.1; 95% CI: 1.4, 3.1), first stage of labor longer than 420 min (OR: 2.3, 95% CI: 1.3,4.2), and a prolonged second stage of labor (OR: 1.6, 95% CI: 1.1, 2.4). CONCLUSION: Age over 35 years and induction of labor are risk factors for forceps delivery at admission. Epidural use, fetal head in occiput posterior position, and birth weight >4000 g are strong intrapartum risk factors for instrumental delivery in nulliparous women.     

持续性枕后位的临床特点及分娩方式选择

目的探讨持续性枕后位的临床特点及分娩方式。方法采用回顾性分析方法，对1998年1月至2004年12月在重庆医科大学两所附属医院住院分娩的112例持续性枕后位（枕后位组）和112例枕前位（枕前位组）的临床资料进行分析，比较两组产程情况、分娩方式及母儿结局。结果两组头位分娩评分、第一产程、第二产程及总产程时间比较，差异有显著性意义（P〈0．05）。枕后位组产钳助产、剖宫产、会阴裂伤、产后出血、胎儿窘迫、新生儿窒息率等均明显高于枕前位组，差异均有显著性意义（P〈0．05）。枕后位组宫口扩张及胎头下降延缓和第二产程延长的发生率均高于枕前位组，差异均有显著性意义（P〈0．05）。剖宫产组富口扩张延缓、胎头下降停滞和第二产程延长的发生率明显高于阴道分娩组（P〈0．05）。而剖宫产组和阴道分娩组骨盆临界狭窄、潜伏期及活跃期延长的发生率比较，差异无显著性意义（P〉0．05）。结论持续性枕后位导致母儿并发症增加，及时处理并选择最佳分娩方式可减少母儿并发症的发生。     

Vaginal versus ultrasound examination of fetal occiput position during the second stage of labor

OBJECTIVE: The purpose of this study was to determine whether ultrasonography is more accurate than vaginal examination in the determination of fetal occiput position in the second stage of labor. STUDY DESIGN: Eighty-eight patients in the second stage of labor were evaluated by vaginal examination and by combined transabdominal and transperineal ultrasound examination to determine occiput position. These predictions of position were compared with the actual delivery position at vaginal delivery after spontaneous restitution or at cesarean delivery. Different examiners performed the vaginal examinations and the ultrasound examinations. Each examiner was blinded to the determination of the other examiner. RESULTS: Vaginal examination determined fetal occiput position correctly 71.6% of the time; ultrasound examination determined fetal occiput position correctly 92.0% of the time (P=.018). CONCLUSION: Ultrasound examination is more accurate than vaginal examination in the diagnosis of fetal occiput position in the second stage of labor.     

Asynclitism: a literature review of an often forgotten clinical condition

Asynclitism is defined as the “oblique malpresentation of the fetal head in labor”. Asynclitism is a clinical diagnosis that may be difficult to make; it may be found during vaginal examination. It is significant because it may cause failure of progress operative or cesarean delivery. We reviewed all literature for asynclitism by performing an extensive electronic search of studies from 1959 to 2013. All studies were first reviewed by a single author and discussed with co-authors. The following studies were identified: 8 book chapters, 14 studies on asynclitism alone and 10 papers on both fetal occiput posterior position and asynclitism. The fetal head in a laboring patient may be associated with some degree of asynclitism; this is seen as usual way of the fetal head to adjust to maternal pelvic diameters. However, marked asynclitism is often detected in presence of a co-existing fetal head malposition, especially the transverse and occipital posterior positions. Digital diagnosis of asynclitism is enhanced by intrapartum ultrasound with transabdominal or transperineal approach. The accurate diagnosis of asynclitism, in an objective way, may provide a better assessment of the fetal head position that will help in the correct application of vacuum and forceps, allowing the prevention of unnecessary cesarean deliveries.     

Intrapartum sonography to determine fetal head position

Objective: To investigate the accuracy of intrapartum transvaginal digital examination in defining the position of the fetal head. Patients and methods: In 496 singleton pregnancies in labor at term, the fetal head position was determined by routine transvaginal digital examination by the attending midwife or obstetrician. Immediately before or after the clinical examination, the fetal head position was determined using transabdominal ultrasound by an appropriately trained sonographer who was not aware of the clinical findings. The digital examination was considered to be correct if the fetal head position was within 45° of the ultrasound finding. The accuracy of the digital examination was examined in relation to maternal characteristics and the progress of labor. Results: The position of the fetal head was determined by ultrasound examination in all 496 cases examined. Digital examination failed to define the fetal head position in 166 (33.5%) cases and, in 330 cases where the position was determined, the findings of the digital and sonographic examinations were in agreement in only 163 (49.4%) cases. The rate of correct identification of the fetal position by digital examination increased with cervical dilatation, from 20.5% at 3–4 cm to 44.2% at 8–10 cm, and was higher if the examination was carried out by an obstetrician than a midwife (50% versus 30%) and if there was absence rather than presence of caput (33% versus 25%). Conclusions: Routine digital examination during labor fails to identify the correct fetal position in the majority of cases.     

Dystocia in late labor: determining fetal position by clinical and ultrasonic techniques

A failure of adequate progression during late labor occurs often and may prohibit an accurate determination of the fetal head position from scalp edema or caput formation. This investigation was undertaken to determine whether ultrasonic evaluation could confirm or correct the digital examination impressions of the fetal head position. Eighty-six attempted vaginal deliveries had recent evidence for arrested cervical dilation after 7 cm or more. An occiput transverse position in 24 (28%) cases was diagnosed accurately, with the need for additional ultrasonic information only in the presence of scalp edema. Distinguishing between a persistent occiput posterior (15 cases, 17%) or anterior (47 cases, 55%) position was often inexact by palpation alone. Combined clinical and ultrasonic impressions allowed for a significantly more precise diagnosis. Ultrasonic imaging allowed for more security while waiting, more confidence with midforceps application, or a prompter decision for cesarean section, depending on the head position.     

Associated factors and outcomes of persistent occiput posterior position: A retrospective cohort study from 1976 to 2001

Objective. To identify maternal and fetal risk factors associated with persistent occiput posterior position at delivery, and to examine the association of occiput posterior position with subsequent obstetric outcomes.

Methods. This is a retrospective cohort study of 30 839 term, cephalic, singleton births. Women with persistent occiput posterior (OP) position at delivery were compared to those with occiput anterior (OA) position. Demographics, obstetric history, and labor management were evaluated and subsequent obstetric outcomes examined. Potential confounding variables were controlled for using multivariate logistic regression analysis.

Results. The overall frequency of OP position was 8.3% in the study population. When compared to Caucasians, a higher rate of OP was observed among African-Americans (OR = 1.4, 95% CI 1.25–1.64) while no other racial/ethnic differences were noted. Other associated factors included nulliparity, maternal age ≥35, gestational age ≥41 weeks, and birth weight >4000 g, as well as artificial rupture of the membranes (AROM) and epidural anesthesia (p < 0.001 for all). Persistent OP was associated with increased rates of operative vaginal (OR = 4.14, 95% CI 3.57–4.81) and cesarean deliveries (OR = 13.45, 95% CI 11.94–15.15) and other peripartum complications including third or fourth degree perineal lacerations (OR = 2.38, 95% CI 2.03–2.79), and chorioamnionitis (OR = 2.10, 95% CI 1.81–2.44).

Conclusion. Epidural use, AROM, African-American ethnicity, nulliparity, and birth weight >4000 g are associated with persistent OP position at delivery, with higher rates of operative deliveries and obstetric complications. This information can be useful in counseling patients regarding risks and associated outcomes of persistent OP position.     

Can measurement of cervical length,fetal head position and posterior cervical angle be an alternative method to Bishop score in the prediction of successful labor induction?

Aim: The purpose of this study was to evaluate sonographic cervical length, posterior cervical angle and fetal head position in predicting successful induction of labor at term can be an alternative method to Bishop score.

Methods: This prospective observational study recruited 223 women with singleton gestations scheduled for induction of labor at 37–42 weeks. Parity, body mass index, Bishop score, fetal head position, cervical angle measurement and cervical length was investigated to predict successful labor induction. Multiple regression analysis was performed to determine the parameters in the prediction of successful vaginal delivery within 24 hours.

Results: Forty-five patients were excluded because of cesarean section performed for other reasons than arrest of dilation or fetal head descent (43 fetal distress, 2 cord prolapsus). Remaining 178 patients were divided into two groups according to duration of delivery time. 139 patients delivered within 24 hours were classified as group I, 39 patients delivered after 24 hours were classified as group II. Percentage of multiparity was statistically significantly higher in group I than in group II [59 (42.4%), 9 (23.0%) respectively, p?=?0.009]. Cervical length was statistically significantly shorter in group I than in group II [23.1?±?7.42?mm, 31.3?±?6.83?mm respectively, p?<?0.001]. Bishop score was statistically significantly higher in group I than in group II [3 (1–4), 1 (1–4) respectively, p?<?0.001]. Posterior cervical angle was statistically significantly higher in group I than in group II [100.1?±?17.2, 92.7?±?21.4 respectively, p?=?0.007]. According to the fetal head position, there was no statistically significant difference in labor duration between the groups (p?=?0.787). In the multivariate regression analysis of variables, multiparity, cervical length and Bishop score were statistically significantly predictive in successful labor induction.

Conclusion: Multiparity status, cervical length, posterior cervical angle and Bishop score can predict successful labor induction, but fetal head position is not predictive in successful labor induction.     

Fetal head position during the second stage of labor: comparison of digital vaginal examination and transabdominal ultrasonographic examination

OBJECTIVE: To study the correlation between digital vaginal and transabdominal ultrasonographic examination of the fetal head position during the second stage of labor. METHODS: Patients (n = 110) carrying a singleton fetus in a vertex position were included. Every patient had ruptured membranes and a fully dilated cervix. Transvaginal examination was randomly performed either by a senior resident or an attending consultant. Immediately afterwards, transabdominal ultrasonography was performed by the same sonographer (OD). Both examiners were blind to each other's results. Sample size was determined by power analysis. Confidence intervals around observed rates were compared using chi-square analysis and Cohen's Kappa test. Logistic regression analysis was performed. RESULTS: In 70% of cases, both clinical and ultrasound examinations indicated the same position of the fetal head (95% confidence interval, 66-78). Agreement between the two methods reached 80% (95% CI, 71.3-87) when allowing a difference of up to 45 degrees in the head rotation. Logistic regression analysis revealed that gestational age, parity, birth weight, pelvic station and examiner's experience did not significantly affect the accuracy of the examination. Caput succedaneum tended to diminish (p = 0.09) the accuracy of clinical examination. The type of fetal head position significantly affected the results. Occiput posterior and transverse head locations were associated with a significantly higher rate of clinical error (p = 0.001). CONCLUSION: In 20% of the cases, ultrasonographic and clinical results differed significantly (i.e., >45 degrees). This rate reached 50% for occiput posterior and transverse locations. Transabdominal ultrasonography is a simple, quick and efficient way of increasing the accuracy of the assessment of fetal head position during the second stage of labor.     

Determination of fetal occiput position by ultrasound during the second stage of labor

Objective: To investigate whether ultrasonography is superior to vaginal examination for determination of fetal occiput position during the second stage of labor. Methods: We conducted a prospective cohort study of 44 parturients. During the second stage of labor, an attending obstetrician performed a vaginal examination to detect fetal occiput position. This was followed by combined abdominal and perineal ultrasound examination. The two methods were compared to the true position. Results were analyzed using Student's t test for quantitative parameters. McNemar's and Fisher's exact tests were applied in order to examine differences between the study groups. Results: The error rate in detecting fetal occiput position was significantly lower using the ultrasound technique (6.8%) compared to vaginal examination (29.6%, p = 0.011). Parity, maternal body mass index or fetal weight had no influence on the error rate. Conclusions: Ultrasonographic determination of the fetal position is an accurate technique and is superior to vaginal examination.     

手转胎头适宜时机的临床观察

目的:探讨头位难产时,选择适宜时机进行手转胎头,以加速产程进展,提高自然分娩率。方法:选择2009年1月至2010年12月共192例单胎头位,持续性枕横位、枕后位,无严重并发症及合并症的产妇,分为观察组96例,对产妇选择适宜时机(宫口开大6～10cm,胎先露在坐骨棘平或坐骨棘下1～2cm)进行手转胎头;对照A组53例,对产妇选择宫口开大<6cm,胎先露在坐骨棘上进行手转胎头;对照B组43例,选择宫口开全后,胎先露在坐骨棘下≥2cm进行手转胎头。结果:观察组手转胎头成功率明显高于对照组(P<0.01);观察组阴道分娩率显著高于对照组,剖宫产率显著低于对照组(P<0.01);产程进展时间、分娩方式、产后出血、新生儿1分钟阿普加评分等与对照组比较差异有高度统计学意义(P<0.01);新生儿窒息率明显降低。结论:手转胎头是处理头位难产的重要方法,选择适宜的时机进行手转胎头,使难产变为顺产,可缩短产程,提高自然分娩率,有效降低阴道助产及剖宫产率,减少母婴并发症。     

The impact of occiput posterior fetal head position on the risk of anal sphincter injury in forceps-assisted vaginal deliveries

OBJECTIVE: A forceps-assisted vaginal delivery is a well-recognized risk factor for anal sphincter injury. Some studies have shown that occiput posterior (OP) fetal head position is also associated with an increased risk for third- or fourth-degree lacerations. The objective of this study was to assess whether OP position confers an incrementally increased risk for anal sphincter injury above that present with forceps deliveries. STUDY DESIGN: This was a retrospective cohort study of 588 singleton, cephalic, forceps-assisted vaginal deliveries performed at our institution between January 1996 and October 2003. Maternal demographics, labor and delivery characteristics, and neonatal factors were examined. Statistical analysis consisted of univariate statistics, Student t test, chi2, and logistic regression. RESULTS: The prevalence of occiput anterior (OA) and OP positions was 88.4% and 11.6%, respectively. The groups were similar in age, marital status, body mass index, use of epidural, frequency of inductions, episiotomies, and shoulder dystocias. The OA group had a higher frequency of rotational forceps (16.2% vs 5.9%, P = .03), greater birth weights (3304 +/- 526 g vs 3092 +/- 777 g, P = .004), and a larger percentage of white women (48.8% vs 34.3%, P = .04). Overall, 35% of forceps deliveries resulted in a third- or fourth-degree laceration. Anal sphincter injury occurred significantly more often in the OP group compared with the OA group (51.5% vs 32.9%, P = .003), giving an odds ratio of 2.2 (CI: 1.3-3.6). In a logistic regression model that controlled for occiput posterior position, maternal body mass index, race, length of second stage, episiotomy, birth weight, and rotational forceps, OP head position was 3.1 (CI: 1.6-6.2) times more likely to be associated with anal sphincter injury than OA head position. CONCLUSION: Forceps-assisted vaginal deliveries have been associated with a greater risk for anal sphincter injury. Within this population of forceps deliveries, an OP position further increases the risk of third- or fourth-degree lacerations when compared with an OA position.     

Determination of fetal occiput position by ultrasound during the second stage of labor

OBJECTIVE: To investigate whether ultrasonography is superior to vaginal examination for determination of fetal occiput position during the second stage of labor. METHODS: We conducted a prospective cohort study of 44 parturients. During the second stage of labor, an attending obstetrician performed a vaginal examination to detect fetal occiput position. This was followed by combined abdominal and perineal ultrasound examination. The two methods were compared to the true position. Results were analyzed using Student's t test for quantitative parameters. McNemar's and Fisher's exact tests were applied in order to examine differences between the study groups. RESULTS: The error rate in detecting fetal occiput position was significantly lower using the ultrasound technique (6.8%) compared to vaginal examination (29.6%, p = 0.011). Parity, maternal body mass index or fetal weight had no influence on the error rate. CONCLUSIONS: Ultrasonographic determination of the fetal position is an accurate technique and is superior to vaginal examination.