Medline ® Abstracts for References 1-5

OBJECTIVE: To use intrapartum sonography as a tool to investigate the development of the persistent occiput posterior position during labor, as well as to identify parameters correlating with the outcome of labor.

METHODS: A prospective study of 408 women in labor after 37 weeks' gestation with a singleton fetus in a vertex position using sonography at the onset of labor was performed. Fetal position, placental location, and maternal BMI (body mass index) were recorded. Outcome of labor was monitored for all relevant parameters.

RESULTS: Most (68%) of persistent occiput posterior positions develop through a malrotation during labor from an initially occipitoanterior position. Only 32% of persistent cases were occipitoposterior (dorsoposterior) at the onset of labor; operative interventions were required in 87.5% of these. Of the 61 (15%) occipitoposterior positions at the onset of labor, 53 (87%) rotated into an occiput anterior position. Persistent occiput posterior position was more common in the initially occipitoposterior group (P<0.01, Fisher exact test), and posterior placental locations were fewer (z test, P = 0.05). Also, operative deliveries were more common in the group remaining occipitoposterior throughout labor (P<.01, Fisher exact test). A higher maternal BMI correlated with neonatal weight (P<.01, Pearson correlation), an increase in operative deliveries (P = .032, Pearson correlation), lower Apgar scores at 1 minute (P = .02, Spearman correlation), and increase in posterior placental locations (P = .037, two-tailed t test).

CONCLUSION: In most cases, persistent occiput posterior position develops through a malrotation and only in a little more than one-third of cases through absence of rotation from an initially occipitoposterior position. Higher maternal BMI correlates with higher fetal weight, increased operative deliveries, lower Apgar scores at 1 minute, and posterior placental locations. Intrapartum sonography proved to be useful in investigating the development of the persistent occipitoposterior position.

OBJECTIVE: To assess clinical and sonographic fetal head position before induction of labor, position at delivery, and whether occiput posterior (OP) position is associated with adverse delivery outcome.

METHODS: Abdominal palpation and ultrasonographic fetal head and spine position were determined at 36 weeks or more of gestation in 289 women immediately before induction of labor and the head position at delivery noted. Chi-square, Mann-Whitney U tests, and logistic regression were used to assess whether OP position was associated with cesarean delivery.

RESULTS: Ninety-seven (36%) of 270 women with full outcome data had an OP position on ultrasonography before induction of labor. Of these 97 women, eight (8%) were OP at delivery. Sixty-eight percent of the 25 OP positions at delivery occurred due to a mal-rotation from a non-OP position during labor. Logistic regression showed that OP position before induction of labor was not an independent predictor of cesarean delivery (odds ratio 1.75, 95% confidence interval 0.97-3.15, P=.06).

CONCLUSION: Two thirds of OP positions at delivery after induction of labor occur due to a mal-rotation in labor from a non-OP position. Ultrasonography is an easy method of assessing fetal head position before induction of labor. In clinical practice, its usefulness is limited by the fact that, contrary to conventional teaching, OP position before induction of labor does not appear to be associated with an increased risk of cesarean delivery.

LEVEL OF EVIDENCE: II.

OBJECTIVES: To assess the relationship between fetal head position and head station during labor, as measured using an ultrasound-based system, and the occurrence of occiput posterior (OP) position at delivery.

METHODS: This was an international prospective observational study including women who delivered between January 2009 and September 2013 in four centers: one in Brooklyn, NY, USA; one in Haifa, Israel; and two in Paris, France. We used an ultrasound-based system (LaborPro) to monitor fetal head station and position non-invasively throughout labor. We collected data on demographics, labor parameters and outcome.

RESULTS: A total of 595 women were included. In 563 (94.6%) women, fetal head position at delivery was occiput anterior (OA), in 31 (5.2%) it was OP and in one (0.2%) it was occiput transverse. In 89% of pregnancies with intrapartum OP when fetal head station was above -2, the head position turned to OA at delivery; the equivalent figures were 74% and 63% OA at delivery when intrapartum OP was diagnosed at head stations of -2 to<0, and 0 andbelow, respectively. Cesarean delivery was performed in 35% of pregnancies with fetal head in OP position at delivery, as opposed to 10% of those with non-OP position at delivery. On retrospective analysis, all deliveries in OP were already in OP at station -2 and below.

CONCLUSIONS: In this first assessment of fetal head position at delivery according to fetal head position at various station levels, our data show that 100% of OP positions at delivery were already in OP position at station -2 and below. We did not observe rotation from a non-OP to an OP position from station -2 and below. Nearly two-thirds of fetuses in OP at station 0 and below will rotate to an OA position for delivery.

OBJECTIVE: To investigate if occiput posterior delivery is the consequence of persistence of an initial occiput posterior position or malrotation from an initial occiput anterior or transverse position.

METHODS: This was a cross-sectional study involving transabdominal sonography to determine fetal occipital position in 918 singleton pregnancies with cephalic presentation in active labor at 37-42 weeks of gestation. The relationship between occipital position in labor and at delivery was examined.

RESULTS: The occiput was posterior in 33.0% (149/452), 33.9% (101/298) and 19.0% (32/168) of fetuses at the respective cervical dilatations of 3-5, 6-9 and 10 cm and this persisted at delivery in 21.5% (32/149), 31.7% (32/101) and 43.8% (14/32) of cases. In 70% (32/46), 91% (32/35) and 100% (14/14) of occiput posterior deliveries there was persistence from this position at 3-5, 6-9 and 10 cm of cervical dilation.

CONCLUSIONS: The majority of occiput posterior positions during labor rotate to the anterior position even at 10 cm of cervical dilatation. However, the vast majority of occiput posterior positions at delivery are a consequence of persistence of this position during labor rather than malrotation from an initial occiput anterior or transverse position.

OBJECTIVE: To assess the feasibility of transabdominal ultrasound for determining fetal head position in laboring women and compare it to digital examination, and to study ultrasonographically the rotation of the fetal head in normal and obstructed labor.

DESIGN: This was an observational prospective study of 148 women in active labor. Ultrasound examinations were performed longitudinally in the first and second stages of labor.

RESULTS: Assessment of the fetal head position by digital examination was not possible in 60.7% (122/201) of cases in the first stage and 30.8% (41/133) in the second stage of labor. Difficulty in assessing the position was more likely if the occiput was posterior in comparison to anterior and in the maternal right in comparison to the left side. In the second stage, it was three times more likely for the assessment not to be possible digitally if the occiput was posterior. In the cases when assessment by vaginal examination was possible, the correlation with ultrasound was average in the first stage (kappa = 0.59) and good in the second stage (kappa= 0.77). Overall fetal head position assessment by digital examination was accurate in 31.28% of the cases in the first stage and 65.7% of the cases in the second stage of labor. Rotation of the fetal head is highly unlikely when labor begins in the occipital anterior position. Persistent occipital posterior position developed through failure to rotate from an initial occipital posterior or transverse position. Duration of the first stage of labor was independently related to parity and position of the fetal spine at presentation, and duration of the second stage of labor was independently related to parity, birth weight, position of the fetal head at the beginning of the second stage, rotation and position of the head at delivery.

CONCLUSION: Ultrasound assessment of the fetal head position in labor is feasible in a busy labor ward. Digital examination is less accurate than ultrasound, in particular in cases of obstructed labor when medical intervention is more likely to be needed. Ultrasound assessment may prove useful in the prediction and diagnosis of difficult and prolonged labor.