Occiput posterior position

INTRODUCTION — Occiput posterior (OP) position is the most common fetal malposition. It is important because it is associated with labor abnormalities that may lead to adverse maternal and neonatal consequences, particularly operative vaginal or cesarean birth. This topic will review issues related to the occurrence, diagnosis, and management of OP position. Other fetal malpositions, as well as diagnosis and management of labor abnormalities, are reviewed separately:

●(See "Occiput transverse position".)

●(See "Compound fetal presentation".)

●(See "Face and brow presentations in labor".)

●(See "Overview of breech presentation" and "Delivery of the singleton fetus in breech presentation".)

●(See "Labor: Overview of normal and abnormal progression".)

PREVALENCE AND PATHOGENESIS — The prevalence of OP position depends on how and when the diagnosis is made. At term, before labor and in early labor, studies have reported that 15 to 50 percent of fetuses in cephalic presentation are OP [1], but only 5 percent are OP at vaginal birth because most OP fetuses spontaneously rotate to an anterior position during labor, usually just before or during full cervical dilation [1-6]. The large variation in prevalence before full dilation has been attributed to differences in the study investigator's definition and assessment of OP.

Some persistent OP positions may be due to an android maternal pelvis, as the mechanical forces on the fetus during the cardinal movements of labor in this setting can inhibit rotation to the occiput anterior (OA) position. In some cases, the OP position at birth results from malrotation from an OA or occiput transverse (OT) position early in labor [3]; spontaneous rotations are unlikely once the second stage has begun [7].

RISK FACTORS — Reported risk factors for OP position at birth include [7-15]:

●Nulliparity

●Obesity

●Previous OP delivery

●Epidural anesthesia

●Birth weight ≥4000 grams

●Gestational age ≥41 weeks

●Black race

●Small pelvic outlet (particularly narrow subpubic arch)

●Maternal age >35 years

●Anterior placenta

Epidural anesthesia has been evaluated most extensively, in part because it is a modifiable risk factor.

Epidural anesthesia — Whether epidural anesthesia is a risk factor for OP position at birth is controversial. Most studies, but not all [16,17], have observed that epidural anesthesia is more likely to be in place when the fetal position at birth is OP than when it is occiput anterior (OA) [7-10,13,16]. The following lines of evidence suggest that relaxation of the pelvic musculature from epidural anesthesia may inhibit rotation from OP to OA, resulting in persistent OP position. These data also dispute the hypothesis that parturients with OP fetuses request epidurals more often than those with OA fetuses because OP position causes more painful labor, thus accounting for the association.

●A prospective cohort study performed serial ultrasound examinations of fetal position at study enrollment, at epidural administration or at four hours after the initial sonogram if no epidural was administered, and after 8 cm dilation; position at birth was also assessed [7]. The study group included over 1500 nulliparous parturients with term singleton cephalic presentations; 92 percent of the participants received a labor epidural. Major findings were:

•Epidural anesthesia increased the chances of OP position at birth – Parturients who requested epidurals and those who did not receive labor epidurals had a similar proportion of fetuses in OP position in early active labor; however, at birth, the epidural group had a statistically higher proportion of OP fetuses (all births: 12.9 versus 3.3 percent; all vaginal births: 10.2 versus 1.9 percent).

•The OP position did not appear to cause more painful labors or "back labor." At the time of the request, parturients who requested epidurals were no more likely to have a fetus in the OP position than those who did not request epidurals: The proportion of fetuses in the OP position was the same at the time of epidural placement and four hours after study enrollment if an epidural was not placed.

●In a meta-analysis of four randomized trials of epidural versus non-epidural or no analgesia in labor, the epidural group had a higher frequency of malposition at birth (relative risk 1.40, 95% CI 0.98-1.99), although the possibility of no effect could not be excluded [18]. Malposition was defined by the trial authors and not limited to OP.

CONSEQUENCES — Potential maternal and neonatal consequences of OP position are summarized in the table (table 1).

●Maternal consequences – OP position may result in protraction of the first or second stage of labor, or arrest of the second stage. In one study, the second stage was approximately 45 minutes longer in OP than occiput anterior (OA) position [12]. Because the OP position can prolong labor, parturients with an OP fetus are more likely to undergo interventions to hasten labor progress, such as iatrogenic rupture of membranes, oxytocin augmentation, and operative birth [8,9,12,13,16,19-24]. Compared with the OA position, OP position was associated with an almost twofold increase in the rate of operative vaginal birth (44 versus 24 percent) and a threefold increase in the rate of cesarean birth (42 versus 14 percent) in a series of over 16,000 nulliparas with singleton cephalic presentations [13]. Other birth-related consequences of OP include increased risks of anal sphincter injuries, failed forceps- or vacuum-assisted birth , and inadvertent extension of the hysterotomy at cesarean. Potential consequences of a prolonged first or second stage of labor include postpartum hemorrhage, chorioamnionitis, and postpartum endometritis [8,25,26].

●Neonatal consequences – Neonatal outcomes associated with birth in the OP position include a higher risk of five-minute Apgar score less than 7 (odds ratio [OR] 1.5, 95% CI 1.17-1.91), umbilical artery acidemia (OR 2.92, OR 1.84-4.62), meconium-stained amniotic fluid (OR 1.29, 95% CI 1.17-1.42), birth trauma (OR 1.77, 95% CI 1.22-2.57), and neonatal intensive care admission (OR 1.57, 95% CI 1.28-1.92) [27]. However, these risks were attenuated or disappeared when adjusted for confounders. Vaginal birth of the OP fetus is associated with a lower rate of shoulder dystocia than other cephalic positions, although there appears to be a higher rate of neonatal brachial plexus injury in the event of a shoulder dystocia [28].

DIAGNOSIS — In the second stage, OP (or occiput transverse) position may be suspected if significant caput succedaneum or asynclitism is present, or labor is prolonged. The diagnosis of OP position is made when digital vaginal examination identifies the anterior position of the fetal frontal (metopic) and coronal sutures and anterior fontanel (figure 1).

However, physical examination is subjective and its accuracy is dependent on the operator's experience. Increasingly, studies have reported that ultrasound is a more accurate and objective tool for the assessment of fetal head position [29-32]. As an example, in one randomized trial, digital examination prior to assisted vaginal birth incorrectly diagnosed position in 20 percent of cases whereas ultrasound assessment was incorrect in only 1.6 percent of cases [33]. Therefore, ultrasound examination should be considered to confirm OP position when operative vaginal birth is planned or in cases of diagnostic uncertainty in the second stage when accurate information is required for clinical decision-making.

Ultrasound technique — The transducer is held transabdominally in the transverse position just above the symphysis pubis, and OP position is diagnosed when the fetal orbits face towards the transducer (image 1).

The fetal spine position can also be followed to identify the fetal occiput. If the top of the presenting fetal head is thought of like a clock face, occiput positions >3:30 and <8:30 can be considered OP (figure 2) [34]. Flexion is inferred if the chin is resting on the chest on a profile view.

If an external fetal heart rate monitor is being used, it should be removed or turned off temporarily during the ultrasound examination as it can interfere with the clarity of the diagnostic images.

MANAGEMENT — The following approach to management of OP position is largely based on the authors' experience, expert opinion, and observational data. Potential interventions have not been evaluated by large randomized trials, with the exception of maternal positioning and digital/manual rotation.

Antepartum — OP position antepartum is not predictive of fetal position at birth or adverse outcome. Therefore, diagnosis of malposition should not be sought antepartum, and if diagnosed, no intervention is necessary.

Pregnant patients are sometimes advised to perform exercises to facilitate anterior rotation of the fetus, but there is no convincing evidence that these maneuvers are effective or any intervention is warranted to reduce the rate of cesarean birth [35,36]. The lack of benefit was best illustrated by a large, multicenter, randomized trial that assigned 2547 pregnant people at 36 to 37 weeks of gestation to one of two exercise programs [35]. Group 1 was told to take a daily walk and Group 2 was asked to assume a hands-and-knees position with slow pelvic rocking for 10 minutes twice daily until labor began. The incidence of OP position at birth or before instrumental rotation/delivery was similar (8 percent) for both groups.

Intrapartum

First stage of labor — Diagnosis of OP need not be sought in the first stage of labor, and if diagnosed, no intervention is necessary. Most malpositions (OP or occiput transverse [OT]) spontaneously rotate to occiput anterior (OA) [1]. OP position in the first stage is a poor predictor of the eventual need for cesarean birth [37] and neither digital/manual rotation nor hands-and-knees positioning [38] has been proven beneficial. Furthermore, digital/manual rotation in the first stage may lead to prolapse of the umbilical cord or small parts if the head is disengaged [39,40] and is less successful than rotation in the second stage [39].

In a meta-analysis of five randomized trials of hands-and-knees positioning (n = 1727) to correct malposition either antepartum at >36 weeks or in the first stage of labor versus no intervention (n = 1641), the frequency of OA position in second stage of labor or at birth was the same in both groups (81.2 percent; RR 1.03, 95% CI 0.92-1.14) [38]. The frequency of OA position was also similar in both groups immediately after the intervention (34.1 versus 18.0 percent; RR 1.60, 95% CI 0.88-2.90). On a posthoc subgroup analysis limited to patients in whom malposition was diagnosed by ultrasound (a more accurate diagnosis), there was a higher rate of OA position immediately after the intervention (17.0 versus 10.3 percent; RR 1.63, 95% CI 1.06-2.52); however, this finding did not persist at birth.

Second stage of labor — Expectant management is also appropriate for OP position early in the second stage as long as the fetal heart rate pattern is reassuring and labor is progressing. Although OP position at this stage increases the chances of cesarean birth [8,16], 50 to 80 percent of OP fetuses at the beginning of the second stage will rotate spontaneously to OA, justifying an expectant approach [25]. Head engagement does not preclude the possibility of spontaneous rotation.

Fetuses in persistent OP position with a normal fetal heart rate tracing may continue to descend at a reasonable rate and deliver spontaneously from the OP position or descent may become protracted or arrested despite adequate uterine contractions and maternal expulsive efforts. The optimal management of second stage protraction or arrest associated with OP position is unclear. Few randomized trials and nonrandomized studies have been conducted comparing the various approaches (rotation versus expectant management, rotation manually or with forceps, operative vaginal birth from OP position, cesarean birth).

For patients with a prolonged second stage and clinically adequate pelvis for rotation, we attempt digital/manual rotation to the OA position, which has a high success rate (up to 93 percent [39,41]), may increase the likelihood of vaginal birth [41,42], may shorten the second stage [43], and has a low risk of maternal and fetal complications (eg, cervical laceration, fetal distress necessitating expeditious delivery) [25].

We perform rotation during the second stage as soon as descent slows, as digital/manual rotation before an arrest is more likely to be successful than after an arrest has occurred [39] and spontaneous rotation is less likely after arrest. We wait until descent slows to intervene rather than routinely at the beginning of the second stage because meta-analyses of randomized trials have not demonstrated benefits from prophylactic digital/manual rotation [44,45].

If the rotation is successful, the patient continues to push and is managed according to usual clinical standards. If the rotation is unsuccessful, the patient continues to push and subsequent intervention depends on labor progress and fetal status. If arrest of descent occurs (eg, no descent after one hour of adequate pushing) or concern about the fetal heart rate tracing warrants delivery, we will attempt operative vaginal birth from the OP position (ie, without rotation to OA) if the leading point of the fetal skull is ≥2 cm beyond the ischial spines, estimated fetal weight is <4000 grams, and there is ample room between the fetal occiput and maternal sacrum/coccyx. In assessing station, it is important to determine whether the biparietal diameter has passed through the pelvic inlet (no more than one-fifth of the fetal head should be palpable abdominally if the vertex is engaged) as extreme molding can falsely suggest engagement. If the prerequisites for a safe operative vaginal birth are not met, then cesarean birth is performed. (See "Assisted (operative) vaginal birth", section on 'Prerequisites'.)

Techniques

Prerotation ultrasound assessment — We do not routinely perform prerotation ultrasound, but we do use it when we are not certain of the precise position of the head and spine.

Some providers routinely perform prerotation ultrasound because they believe it is needed to confirm the diagnosis of OP [33] and information on fetal spine position may improve success rates for digital/manual rotation. In a randomized trial of ultrasound examination of 58 nulliparous patients in second-stage arrest with the fetus in OP position, operators who were informed of the fetal spine position had more successful digital/manual rotations than those who did not have this information (83 versus 41 percent), and their patients had a higher percentage of spontaneous births (69 versus 28 percent) and better maternal outcome (eg, intact perineum, less blood loss) [46]. Neonatal outcomes were similar for both groups.

Digitial/manual rotation — Several techniques for rotation have been described. Our approach follows:

●The majority of our patients elect to have epidural anesthesia for labor. If the patient does not have adequate anesthesia and is not able to tolerate rotation, a pudendal block or intravenous opioids may provide adequate analgesia [47,48].

●The maternal bladder is emptied prior to the procedure.

●We generally begin the rotational process between contractions.

●The operator's hand is inserted into the vagina with the palm upward. Rotation is performed by placing the tips of the index and middle fingers in the anterior segment of the lambdoid suture near the posterior fontanelle (figure 3). The fingers are used to flex and slightly dislodge the head, rotating it to the OA position by rotation of the operator's hand and forearm together. The thumb may be used to exert gentle downward pressure anteriorly on the parietal bone to aid in rotation.

●Rotation can also be performed by placing the operator's four fingers behind the posterior parietal bone with the palm up and the thumb over the anterior parietal bone. The right hand is used for left OP position and the left hand is used for right OP position. The head is grasped with the tips of the fingers and thumb. During a contraction, the patient is encouraged to push and the operator attempts to flex and rotate the fetal head anteriorly using the hand and forearm together (figure 4 and movie 1) [39,49]. Occasional, mild upward pressure may help to slightly displace the head and facilitate rotation.

●The fetal head may need to be held in place for a few contractions to prevent rotation back toward the posterior position.

Multiple attempts at rotation may be required. Rotation performed prior to an operative vaginal birth has little or no increase in risk for the mother or fetus [47,48].

Operative vaginal birth from the OP position — The usual criteria for performance of an operative vaginal birth apply to the OP position. Although often successful, OP position is associated with a significantly higher rate of failed operative vaginal birth than OA position [23]. (See "Assisted (operative) vaginal birth".)

We make our choice of instrument (forceps versus vacuum) based on individual patient factors, weighing the relative risks for success and rectal sphincter injury. As an example, for a tired, nulliparous patient with an edematous perineum and fetus at or near the outlet, we prefer a vacuum over forceps since it is likely to be successful and minimizes maternal trauma. For a multiparous patient at +2/5 station with fetal bradycardia, we prefer forceps because we have better success with forceps- than vacuum-assisted birth in this setting. This approach is supported by data from a retrospective study on OP operative births that reported the success rates for vacuum versus forceps were: outlet procedures, 100 percent for both instruments; low-station procedures, 69 versus 88 percent; and mid-station procedures, 29 versus 83 percent; whereas risk of rectal sphincter injury with vacuum and forceps was 33 and 72 percent, respectively [50]. All of these differences were statistically significant.

If forceps are used, we prefer Simpson forceps because fetuses in OP position often have significant molding. Downward traction should be exerted until the brow clears the symphysis pubis and then the head should be flexed to reduce the risk of an anal sphincter tear during extraction. Our decision to attempt forceps-assisted birth from OP position versus digital/manual rotation to OA and extraction is based on our clinical assessment of the mother and fetus. Forceps-assisted birth from the OP position is preferred in patients with space posteriorly in the pelvis and a narrow anterior segment. Patients with ample space anteriorly and a fetus in persistent OP position may benefit from digital/manual rotation to OA followed by extraction from the OA position.

Although anal sphincter injuries occur more commonly with OP births and operative vaginal births, we do not perform episiotomy routinely as it is not clear that episiotomy results in better overall outcome than not performing episiotomy. If an episiotomy is clinically indicated, a mediolateral episiotomy results in fewer fourth degree lacerations than a midline episiotomy. (See "Approach to episiotomy".)

If vacuum is used, certain adjustments must be made because the cephalic flexion point on OP presentations is located posteriorly and deeper in the vagina than with OA presentations. This is reviewed separately. (See "Procedure for vacuum-assisted vaginal birth", section on 'Cup choice for occiput posterior and deflexed heads'.)

Forceps rotation — Instrument rotation (eg, Kielland forceps rotation [51], Thierry's spatulas rotation [52]) for the persistent OP position should only be performed by clinicians with skill and experience in the performance of these procedures due to the high risk of potential complications. Direct delivery from OP rather than rotation is preferable in patients who on clinical examination have ample room between the fetal occiput and maternal sacrum/coccyx and when the pelvis is too narrow to permit anterior rotation (patients with an anthropoid pelvis with a narrow transverse diameter and patients with an android pelvis with a narrow arch).

Ultrasound can be helpful to confirm the position of the fetal head and spine before placing forceps. If classic forceps, such as Tucker-McLane or Elliot forceps, are used in the Scanzoni maneuver, the forceps are applied as though the head is OA and then the head is flexed and rotated to the OA position. It can be helpful to dislodge the head to a higher station before rotation to facilitate the procedure. After the rotation, a slight pull on the forceps helps to fix the head in the anterior position. The forceps, which are upside down after the rotation, are removed and reapplied one at a time so one forceps splints the head and prevents spontaneous reversion to OP. Forceps-assisted delivery of the head can then be achieved from the anterior position. A more detailed description of these procedures is beyond the scope of this topic review.

Cesarean birth — Cesarean birth is performed using standard techniques. The fetal head may be deeply engaged and impacted. Techniques for safely extracting the fetus in this setting are reviewed separately. (See "Cesarean birth: Management of the deeply impacted head and the floating head", section on 'Deeply impacted fetal head'.)

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Labor".)

SUMMARY AND RECOMMENDATIONS

●Prevalence – Before labor, 15 to 20 percent of term fetuses in cephalic presentation are occiput posterior (OP), but only 5 percent are OP at vaginal birth because most OP fetuses spontaneously rotate to an anterior position during labor. (See 'Prevalence and pathogenesis' above.)

●Consequences – The OP position may prolong labor and arrest descent. Maternal and neonatal morbidity are increased because of the need for interventions to manage these labor abnormalities. (See 'Consequences' above.)

●Diagnosis – Diagnosis of OP position is generally made by digital vaginal examination in the second stage of labor that identifies the anterior location of the fetal frontal (metopic) and coronal sutures and anterior fontanel (figure 1). If there is uncertainty, ultrasound examination can accurately identify fetal head position (figure 2). (See 'Diagnosis' above.)

●Management

•Antepartum, first and early second stage of labor – Intervention to rotate the fetus is not warranted when OP position is diagnosed antepartum, in the first stage of labor, or in the early second stage of labor as spontaneous rotation to occiput anterior (OA) usually occurs. (See 'Antepartum' above and 'First stage of labor' above and 'Second stage of labor' above.)

Maternal exercises and repositioning do not increase the rate of spontaneous rotation. (See 'Antepartum' above and 'First stage of labor' above.)

Prophylactic rotation in the early second stage may lead to prolapse of the umbilical cord or small parts if the head is disengaged, without clear benefits. Head engagement does not preclude the possibility of spontaneous rotation. (See 'Second stage of labor' above.)

As the second stage progresses, fetuses that remain in the OP position may continue to descend at a reasonable rate and deliver spontaneously from the OP position or descent may become protracted or arrested despite adequate uterine contractions and maternal expulsive efforts. (See 'Second stage of labor' above.)

•Prolonged second stage

-For women with a prolonged second stage and clinically adequate pelvis for rotation, we suggest digital/manual rotation to the OA position rather than expectant management (Grade 2C). Rotation at this time has a high success rate, increases the likelihood of vaginal birth, and has low risk of maternal and fetal complications. We perform rotation as soon as descent slows as rotation before an arrest is more likely to be successful than after an arrest has occurred and spontaneous rotation is less likely in this setting. (See 'Second stage of labor' above.)

-If rotation is unsuccessful, the patient continues to push and subsequent intervention depends on labor progress and fetal status. If arrest of descent occurs or concern about the fetal heart rate warrants delivery, we attempt operative vaginal birth from the OP position if the leading point of the fetal skull is ≥2 cm beyond the ischial spines, estimated fetal weight is <4000 grams, and there is ample room between the fetal occiput and maternal sacrum/coccyx. If the prerequisites for a safe operative vaginal birth are not met, then cesarean birth is performed. (See 'Second stage of labor' above.)