Ultrasound Obstet Gynecol 2015; 46: 611–615 Published online in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/uog.14821
Prospective multicenter study of ultrasound-based measurements of fetal head station and position throughout labor D. VITNER*, Y. PALTIELI*, S. HABERMAN†, R. GONEN*, Y. VILLE‡ and J. NIZARD§ *Department of Obstetrics and Gynecology, Bnai Zion Medical Center, Technion, Israel Institute of Technology, Haifa, Israel; †Department of Obstetrics and Gynecology, Maimonides Medical Center, Brooklyn, NY, USA; ‡Department of Obstetrics and Fetal Medicine, Universit´e Paris Descartes, Hopital Necker-Enfants-Malade, Paris, France; §Service de Gyn´ecologie Obst´etrique, Groupe ˆ Hospitalier Piti´e-Salpˆetri`ere, APHP, Sorbonne Universit´es, Paris, France
K E Y W O R D S: fetal head position; fetal head station; LaborPro; occipitoposterior; ultrasound in labor
ABSTRACT 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 and below, 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. Copyright © 2015 ISUOG. Published by John Wiley & Sons Ltd.
INTRODUCTION Occiput posterior (OP) fetal head position occurs in about 25% of pregnancies in the first stage of labor, 15% in the second stage and 5% at the time of delivery1 . OP position is the most common malposition during labor2 – 4 . It is associated with prolongation of both first and second stages of labor, and it increases the rates of Cesarean deliveries, perinatal morbidity and severe maternal perineal lacerations and anal sphincter injury2,5 . The mechanism that leads to OP position at delivery is not entirely understood and the literature on this topic are inconsistent. Akmal et al. and Souka et al. have suggested that OP position at delivery originates from malposition of the fetal head before or during early labor5,6 , whereas Gardberg et al. claim that it is a result of malrotation during labor from an occiput anterior (OA) or occiput transverse (OT) position1 . Recent intrapartum sonographic studies have demonstrated that clinical assessment of fetal head position has limited reliability2 – 5,7 . Intrapartum sonography is considered as the gold standard for assessing the position of the fetal head, but is not yet commonly used for routine monitoring of labor progression2,6 . The aim of this study was to assess the relationship between OP position and fetal head station during labor, both measured using an ultrasound-based system (LaborPro system; Trig Medical Ltd, Nesher, Israel), and to evaluate the use of these findings in predicting OP at delivery.
ˆ Correspondence to: Prof. J. Nizard, Service de Gyn´ecologie Obst´etrique, Groupe Hospitalier Piti´e Salpˆetri`ere, 83, Boulevard de l’Hopital, 75013 Paris, France (e-mail: [email protected]) Accepted: 5 December 2014
Copyright © 2015 ISUOG. Published by John Wiley & Sons Ltd.
ORIGINAL PAPER
Vitner et al.
612
Pubis
Station: intersection point between skull and birth canal
Birth canal centerline
Fetal skull
Figure 1 Screenshot of the LaborPro system showing the center of the birth canal (blue line) and its intersection with the fetal skull and determination of fetal head station.
METHODS We performed a prospective observational study including women who delivered between January 2009 and September 2013. The inclusion criteria were women with singleton uncomplicated cephalic term pregnancies during labor who signed or gave consent. The study was performed at four different sites (Brooklyn, NY, USA; Haifa, Israel; and two centers in Paris, France). The study was approved by local Institutional Review Boards or Ethical Committees. For the purposes of this study, fetal head positions ranging from left occipitoposterior (112.5◦ ) to right occipitoposterior (247.5◦ ) were defined as OP7 . The angle used in this definition was based on a comparison between fetal head position and maternal pelvis position, as provided by the system used. The LaborPro system was used to determine fetal head station and position using ultrasound and a position tracking system, as well as other parameters. The system has received both US Food and Drug Administration clearance and a European CE mark. The systems were provided
Copyright © 2015 ISUOG. Published by John Wiley & Sons Ltd.
by the manufacturer for use in this study. The LaborPro system has previously been described elsewhere7 . In summary, intrapartum assessment is carried out as follows: Step 1: Spatial positioning of the pelvic inlet plane and birth canal – the maternal pelvis is mapped by marking known points on the pelvis using tiny position sensors and ultrasound. With the L5 spinous process marked as a fixed point, measurements are not affected by maternal movements or position. Step 2: Station is determined by infrapubic ultrasound imaging – the superior and inferior limits of the symphysis pubis and the point of intersection between the birth canal and the fetal skull are automatically or manually marked (Figure 1). The system calculates and displays fetal head station in relation to the pelvic inlet plane and birth canal, and provides data instantaneously. The assessment of fetal head position by the system is performed by calculating the spatial position of head
Ultrasound Obstet Gynecol 2015; 46: 611–615.
OP in labor deliver in OA
613
Figure 2 Graphic representation of the fetal head in the maternal pelvis using fetal head station and position data from the LaborPro system.
landmarks relative to the center of the birth canal, by marking one of the following ultrasound landmarks on the screen: biparietal/occipitofrontal diameter, cervical vertebra, midline and orbits. The system graphically presents results according to the measured degree of rotation (Figure 2). Measurements were performed by midwives or physicians. Each series of measurements took between 1 and 2 minutes. We collected data on demographic characteristics, labor parameters and pregnancy outcome.
t-test was used to assess differences in continuous variables between groups. In cases in which station measurements were repeated at a particular point in time, the lowest measurements were used. The association between fetal position measured during labor, stratified by different station levels (above station −2, between station −2 and < 0, and station 0 and below), and head position at delivery was examined using the chi-square test. All P-values were two-sided, and statistical significance was defined as P < 0.05.
Statistical methods Data analysis was performed using the SPSS statistical package version 21.0 (SPSS Inc., Chicago, IL, USA). Descriptive statistics for categorical variables (parity, induction of labor, epidural and mode of delivery) were conducted using frequency tables. For continuous variables (age, fetal weight and body mass index (BMI)), means and SD were given. Comparisons of categorical characteristics between groups (OP vs OA or OT at delivery) were performed using the chi-square test. The
Copyright © 2015 ISUOG. Published by John Wiley & Sons Ltd.
RESULTS A total of 595 women were included in the study. In 563 (94.6%) women, fetal head position at delivery was OA, in 31 (5.2%) deliveries it was OP and in one woman (0.2%) it was OT (diagnosis at Cesarean delivery). There were no statistically significant demographic differences between groups with OP vs OA or OT head position at delivery, except for maternal BMI, which was higher in
Ultrasound Obstet Gynecol 2015; 46: 611–615.
Vitner et al.
614 Table 1 Demographic and delivery characteristics of the study population according to occiput posterior (OP) fetal head position at delivery
Characteristic Maternal age (years) Gestational age (weeks) Epidural analgesia Birth weight (g) BMI (kg/m2 ) Nulliparous Induction of labor CS (%) CS due to NPL (%)† Duration of 2nd stage (h) Vacuum/forceps delivery
OP at delivery (n = 31)
Non-OP at delivery (n = 564)
P*
27.9 ± 7.0 39.9 ± 1.0 96.4 3462 ± 294 27.8 ± 7.8 55.2 17.9 35.5 80.0 1.5 ± 1.1 22.6
28.6 ± 5.5 39.8 ± 1.0 96.4 3355 ± 387 23.1 ± 3.9 56.4 19.0 10.3 53.1 2.0 ± 1.2 17.7
0.5 0.4 0.93 0.09 0.02 0.9 0.9 < 0.001 < 0.001 0.03 0.5
Data given as mean ± SD or % (denominators vary due to missing data). *t-test for continuous variables and chi-square test for categorical variables. †Given as % of total number of Cesarean section (CS) deliveries. BMI, body mass index; NPL, non-progressive labor.
the OP group (Table 1). About half of the women were nulliparous in the OP and non-OP groups. Cesarean delivery was performed in 35% of pregnancies with fetal head in OP at delivery, as opposed to in 10% of pregnancies with non-OP position at delivery (P < 0.001). Non-progressive labor was the indication of 80% of cases of Cesarean delivery in the OP group, but of only half of the cases in the non-OP group (P < 0.001). Moreover, 42% of pregnancies with OP position at delivery had a normal spontaneous vaginal delivery compared with 72% of pregnancies with non-OP position at delivery (Table 1). There was no statistically significant difference in the rate of instrumental vaginal delivery between groups. We found that 89% of pregnancies with fetal head in OP position when the head station was above −2 turned to the OA position at delivery (Table 2), with equivalent figures of 74% and 63% for OA at delivery when a diagnosis of OP was made at a head station of −2 to < 0, and at or below 0, respectively. On retrospective analysis of fetal head position at these three categories of head station level, for cases with OP at delivery all fetuses were already in OP at station −2 and lower, and all fetuses in OA or OT positions at station −2 and below were eventually in the OA position at delivery. Before engagement (i.e. at station −2 to < 0), 103 fetuses were in the OP position (23%); of these, 76 rotated to OA and one to OT, and 26 remained in the OP position at delivery. Sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) are given in Table 3 for a diagnosis of intrapartum OP position in predicting OP position at delivery at each of the three head-station levels.
DISCUSSION In this first assessment of fetal head position at delivery according to fetal head position at various station levels, our data showed that most fetuses in OP during labor, even after engagement of the fetal head, will rotate to
Copyright © 2015 ISUOG. Published by John Wiley & Sons Ltd.
Table 2 Fetal head position at delivery according to fetal head position during labor, as assessed using an ultrasound-based system, stratified by fetal head station at intrapartum assessment Head position at delivery
Head position in labor
OA
Station above −2 OA 29 (96.7) OP 25 (89.3) OT 75 (94.9) Total 129 (94.2) Station between −2 and < 0 OA 250 (100.0) OP 76 (73.8) OT 96 (100.0) Total 422 (94.0) Station at or below 0 OA 223 (100.0) OP 17 (63.0) OT 20 (100.0) Total 260 (96.3)
OP
OT
Total
P 0.48
1 (3.3) 3 (10.7) 4 (5.1) 8 (5.8)
0 (0.0) 30 0 (0.0) 28 0 (0.0) 79 0 (0.0) 137
0 (0.0) 26 (25.2) 0 (0.0) 26 (5.8)
0 (0.0) 250 1 (1.0) 103 0 (0.0) 96 1 (0.2) 449
0 (0.0) 10 (37.0) 0 (0.0) 10 (3.7)
0 (0.0) 223 0 (0.0) 27 0 (0.0) 20 0 (0.0) 270
0.001
0.001
Data given as n (%) or n. OA, occiput anterior; OP, occiput posterior; OT, occiput transverse. Table 3 Sensitivity, specificity and positive (PPV) and negative (NPV) predictive values of diagnosis of fetal occiput posterior (OP) during labor for OP at delivery, stratified according to fetal head station at intrapartum assessment Fetal head station Above −2 Between −2 and < 0 At or below 0
Sensitivity
Specificity
PPV
NPV
37.5 100 100
80.6 82.0 93.5
10.7 25.5 37.0
95.4 100 100
Data given as %.
an OA position for delivery. In this setting, ultrasound showed that all fetuses in OA or OT from station −2 and lower delivered in OA. Moreover, all neonates delivered in OP were already in OP from station −2 and lower. Our study is the first to correlate fetal head position and station during labor, determined by an ultrasound-based device (the LaborPro system), with position at delivery. Hence, because measurements of station and position are automatic or semi-automatic, the data collected are more objective than when position and station are assessed only by ultrasound or vaginal examination. We were able to study a large population, which is important when considering that delivery in OP is relatively rare. Finally, data were collected prospectively in the four centers and fetal head position was therefore assessed even when delivery was performed by Cesarean section. Care providers were not blinded to data provided by the ultrasound-based system, but because the main criterion studied was not the mode of delivery but head position at delivery, this should not influence our conclusions. Our data differ from those of other series in the literature, but most of these other series have used different methodology. Studies of ultrasound assessment of fetal head position in the literature have mostly used either first/second stage1,2,6 or cervical dilatation assessed clinically5,8 as a labor-progression scale. Although there
Ultrasound Obstet Gynecol 2015; 46: 611–615.
OP in labor deliver in OA is a relationship between cervical dilatation assessed clinically and fetal head station assessed by ultrasound9 , we have provided data using fetal head station itself as a labor progression scale. The mechanism leading to OP at delivery is a matter of debate. Gardberg et al. reported that most deliveries in OP were from fetuses in OA during labor1 . This contrasts with data from other authors2,8 and our data. Akmal et al.5 and Souka et al.6 reached different conclusions from Gardberg et al.1 , claiming that the vast majority of cases of OP position at delivery are a consequence of persistence of this position during labor rather than malrotation from an initial OA or OT position5,6 . It seems therefore that OP at delivery results from an absence of rotation from an initial OP position, at least from station −2 and lower. Having the information that the fetal head position is in OP during labor is important. First, it should not influence labor management until late into labor because the vast majority of cases will rotate to OA. Second, it may explain why trials using maternal positioning in labor with fetuses in OP did not show significant improvement after this intervention10,11 . In conclusion, we found that 100% of cases of OP position at delivery were already in OP at station −2 and below. We did not observe rotation from a non-OP to 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.
DISCLOSURE Dr Yoav Paltieli is a senior physician of the OB/GYN Department in Bnai Zion Medical Center, Haifa, Israel,
Copyright © 2015 ISUOG. Published by John Wiley & Sons Ltd.
615
and an officer of Trig Medical Inc., Nesher, Israel, the manufacturer of the LaborPro System. The LaborPro Systems were provided by the manufacturer for use in this study.
REFERENCES 1. Gardberg M, Laakkonen E, Salevaara M. Intrapartum sonography and persistent occiput posterior position: a study of 408 deliveries. Obstet Gynecol 1998; 91: 746–749. 2. Blasi I, D’Amico R, Fenu V, Volpe A, Fuchs I, Henrich W, Mazza V. Sonographic assessment of fetal spine and head position during the first and second stages of labor for the diagnosis of persistent occiput posterior position: a pilot study. Ultrasound Obstet Gynecol 2010; 35: 210–215. 3. Sherer DM, Miodovnik M, Bradley KS, Langer O. Intrapartum fetal head position I: comparison between transvaginal digital examination and transabdominal ultrasound assessment during the active stage of labor. Ultrasound Obstet Gynecol 2002; 19: 258–263. 4. Sherer DM, Miodovnik M, Bradley KS, Langer O. Intrapartum fetal head position II: comparison between transvaginal digital examination and transabdominal ultrasound assessment during the second stage of labor. Ultrasound Obstet Gynecol 2002; 19: 264–268. 5. Akmal S, Tsoi E, Howard R, Osei E, Nicolaides KH. Investigation of occiput posterior delivery by intrapartum sonography. Ultrasound Obstet Gynecol 2004; 24: 425–428. 6. Souka AP, Haritos T, Basayiannis K, Noikokyri N, Antsaklis A. Intrapartum ultrasound for the examination of the fetal head position in normal and obstructed labor. J Matern Fetal Neonatal Med 2003; 13: 59–63. 7. Nizard J, Haberman S, Paltieli Y, Gonen R, Ohel G, Le Bourthe Y, Ville Y. Determination of fetal head station and position during labor: a new technique that combines ultrasound and a position-tracking system. Am J Obstet Gynecol 2009; 200: 404.e1–5. 8. Lieberman E, Davidson K, Lee-Parritz A, Shearer E. Changes in fetal position during labor and their association with epidural analgesia. Obstet Gynecol 2005; 105: 974–982. 9. Haberman S, Paltieli Y, Gonen R, Ohel G, Ville Y, Nizard J. Association between ultrasound-based assessment of fetal head station and clinically assessed cervical dilatation. Ultrasound Obstet Gynecol 2011; 37: 709–711. 10. Desbriere R, Blanc J, Le Du R, Renner JP, Carcopino X, Loundou A, d’Ercole C. Is maternal posturing during labor efficient in preventing persistent occiput posterior position? A randomized controlled trial. Am J Obstet Gynecol 2013; 208: 60.e1–8. 11. Guittier MJ, Othenin-Girard V, Irion O, Boulvain M. Maternal positioning to correct occipito-posterior fetal position in labour: a randomised controlled trial. BMC Pregnancy Childbirth 2014; 14: 83.
Ultrasound Obstet Gynecol 2015; 46: 611–615.
Prospective multicenter study of ultrasound-based measurements of fetal head station and position throughout labor D. VITNER*, Y. PALTIELI*, S. HABERMAN†, R. GONEN*, Y. VILLE‡ and J. NIZARD§ *Department of Obstetrics and Gynecology, Bnai Zion Medical Center, Technion, Israel Institute of Technology, Haifa, Israel; †Department of Obstetrics and Gynecology, Maimonides Medical Center, Brooklyn, NY, USA; ‡Department of Obstetrics and Fetal Medicine, Universit´e Paris Descartes, Hopital Necker-Enfants-Malade, Paris, France; §Service de Gyn´ecologie Obst´etrique, Groupe ˆ Hospitalier Piti´e-Salpˆetri`ere, APHP, Sorbonne Universit´es, Paris, France
K E Y W O R D S: fetal head position; fetal head station; LaborPro; occipitoposterior; ultrasound in labor
ABSTRACT 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 and below, 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. Copyright © 2015 ISUOG. Published by John Wiley & Sons Ltd.
INTRODUCTION Occiput posterior (OP) fetal head position occurs in about 25% of pregnancies in the first stage of labor, 15% in the second stage and 5% at the time of delivery1 . OP position is the most common malposition during labor2 – 4 . It is associated with prolongation of both first and second stages of labor, and it increases the rates of Cesarean deliveries, perinatal morbidity and severe maternal perineal lacerations and anal sphincter injury2,5 . The mechanism that leads to OP position at delivery is not entirely understood and the literature on this topic are inconsistent. Akmal et al. and Souka et al. have suggested that OP position at delivery originates from malposition of the fetal head before or during early labor5,6 , whereas Gardberg et al. claim that it is a result of malrotation during labor from an occiput anterior (OA) or occiput transverse (OT) position1 . Recent intrapartum sonographic studies have demonstrated that clinical assessment of fetal head position has limited reliability2 – 5,7 . Intrapartum sonography is considered as the gold standard for assessing the position of the fetal head, but is not yet commonly used for routine monitoring of labor progression2,6 . The aim of this study was to assess the relationship between OP position and fetal head station during labor, both measured using an ultrasound-based system (LaborPro system; Trig Medical Ltd, Nesher, Israel), and to evaluate the use of these findings in predicting OP at delivery.
ˆ Correspondence to: Prof. J. Nizard, Service de Gyn´ecologie Obst´etrique, Groupe Hospitalier Piti´e Salpˆetri`ere, 83, Boulevard de l’Hopital, 75013 Paris, France (e-mail: [email protected]) Accepted: 5 December 2014
Copyright © 2015 ISUOG. Published by John Wiley & Sons Ltd.
ORIGINAL PAPER
Vitner et al.
612
Pubis
Station: intersection point between skull and birth canal
Birth canal centerline
Fetal skull
Figure 1 Screenshot of the LaborPro system showing the center of the birth canal (blue line) and its intersection with the fetal skull and determination of fetal head station.
METHODS We performed a prospective observational study including women who delivered between January 2009 and September 2013. The inclusion criteria were women with singleton uncomplicated cephalic term pregnancies during labor who signed or gave consent. The study was performed at four different sites (Brooklyn, NY, USA; Haifa, Israel; and two centers in Paris, France). The study was approved by local Institutional Review Boards or Ethical Committees. For the purposes of this study, fetal head positions ranging from left occipitoposterior (112.5◦ ) to right occipitoposterior (247.5◦ ) were defined as OP7 . The angle used in this definition was based on a comparison between fetal head position and maternal pelvis position, as provided by the system used. The LaborPro system was used to determine fetal head station and position using ultrasound and a position tracking system, as well as other parameters. The system has received both US Food and Drug Administration clearance and a European CE mark. The systems were provided
Copyright © 2015 ISUOG. Published by John Wiley & Sons Ltd.
by the manufacturer for use in this study. The LaborPro system has previously been described elsewhere7 . In summary, intrapartum assessment is carried out as follows: Step 1: Spatial positioning of the pelvic inlet plane and birth canal – the maternal pelvis is mapped by marking known points on the pelvis using tiny position sensors and ultrasound. With the L5 spinous process marked as a fixed point, measurements are not affected by maternal movements or position. Step 2: Station is determined by infrapubic ultrasound imaging – the superior and inferior limits of the symphysis pubis and the point of intersection between the birth canal and the fetal skull are automatically or manually marked (Figure 1). The system calculates and displays fetal head station in relation to the pelvic inlet plane and birth canal, and provides data instantaneously. The assessment of fetal head position by the system is performed by calculating the spatial position of head
Ultrasound Obstet Gynecol 2015; 46: 611–615.
OP in labor deliver in OA
613
Figure 2 Graphic representation of the fetal head in the maternal pelvis using fetal head station and position data from the LaborPro system.
landmarks relative to the center of the birth canal, by marking one of the following ultrasound landmarks on the screen: biparietal/occipitofrontal diameter, cervical vertebra, midline and orbits. The system graphically presents results according to the measured degree of rotation (Figure 2). Measurements were performed by midwives or physicians. Each series of measurements took between 1 and 2 minutes. We collected data on demographic characteristics, labor parameters and pregnancy outcome.
t-test was used to assess differences in continuous variables between groups. In cases in which station measurements were repeated at a particular point in time, the lowest measurements were used. The association between fetal position measured during labor, stratified by different station levels (above station −2, between station −2 and < 0, and station 0 and below), and head position at delivery was examined using the chi-square test. All P-values were two-sided, and statistical significance was defined as P < 0.05.
Statistical methods Data analysis was performed using the SPSS statistical package version 21.0 (SPSS Inc., Chicago, IL, USA). Descriptive statistics for categorical variables (parity, induction of labor, epidural and mode of delivery) were conducted using frequency tables. For continuous variables (age, fetal weight and body mass index (BMI)), means and SD were given. Comparisons of categorical characteristics between groups (OP vs OA or OT at delivery) were performed using the chi-square test. The
Copyright © 2015 ISUOG. Published by John Wiley & Sons Ltd.
RESULTS A total of 595 women were included in the study. In 563 (94.6%) women, fetal head position at delivery was OA, in 31 (5.2%) deliveries it was OP and in one woman (0.2%) it was OT (diagnosis at Cesarean delivery). There were no statistically significant demographic differences between groups with OP vs OA or OT head position at delivery, except for maternal BMI, which was higher in
Ultrasound Obstet Gynecol 2015; 46: 611–615.
Vitner et al.
614 Table 1 Demographic and delivery characteristics of the study population according to occiput posterior (OP) fetal head position at delivery
Characteristic Maternal age (years) Gestational age (weeks) Epidural analgesia Birth weight (g) BMI (kg/m2 ) Nulliparous Induction of labor CS (%) CS due to NPL (%)† Duration of 2nd stage (h) Vacuum/forceps delivery
OP at delivery (n = 31)
Non-OP at delivery (n = 564)
P*
27.9 ± 7.0 39.9 ± 1.0 96.4 3462 ± 294 27.8 ± 7.8 55.2 17.9 35.5 80.0 1.5 ± 1.1 22.6
28.6 ± 5.5 39.8 ± 1.0 96.4 3355 ± 387 23.1 ± 3.9 56.4 19.0 10.3 53.1 2.0 ± 1.2 17.7
0.5 0.4 0.93 0.09 0.02 0.9 0.9 < 0.001 < 0.001 0.03 0.5
Data given as mean ± SD or % (denominators vary due to missing data). *t-test for continuous variables and chi-square test for categorical variables. †Given as % of total number of Cesarean section (CS) deliveries. BMI, body mass index; NPL, non-progressive labor.
the OP group (Table 1). About half of the women were nulliparous in the OP and non-OP groups. Cesarean delivery was performed in 35% of pregnancies with fetal head in OP at delivery, as opposed to in 10% of pregnancies with non-OP position at delivery (P < 0.001). Non-progressive labor was the indication of 80% of cases of Cesarean delivery in the OP group, but of only half of the cases in the non-OP group (P < 0.001). Moreover, 42% of pregnancies with OP position at delivery had a normal spontaneous vaginal delivery compared with 72% of pregnancies with non-OP position at delivery (Table 1). There was no statistically significant difference in the rate of instrumental vaginal delivery between groups. We found that 89% of pregnancies with fetal head in OP position when the head station was above −2 turned to the OA position at delivery (Table 2), with equivalent figures of 74% and 63% for OA at delivery when a diagnosis of OP was made at a head station of −2 to < 0, and at or below 0, respectively. On retrospective analysis of fetal head position at these three categories of head station level, for cases with OP at delivery all fetuses were already in OP at station −2 and lower, and all fetuses in OA or OT positions at station −2 and below were eventually in the OA position at delivery. Before engagement (i.e. at station −2 to < 0), 103 fetuses were in the OP position (23%); of these, 76 rotated to OA and one to OT, and 26 remained in the OP position at delivery. Sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) are given in Table 3 for a diagnosis of intrapartum OP position in predicting OP position at delivery at each of the three head-station levels.
DISCUSSION In this first assessment of fetal head position at delivery according to fetal head position at various station levels, our data showed that most fetuses in OP during labor, even after engagement of the fetal head, will rotate to
Copyright © 2015 ISUOG. Published by John Wiley & Sons Ltd.
Table 2 Fetal head position at delivery according to fetal head position during labor, as assessed using an ultrasound-based system, stratified by fetal head station at intrapartum assessment Head position at delivery
Head position in labor
OA
Station above −2 OA 29 (96.7) OP 25 (89.3) OT 75 (94.9) Total 129 (94.2) Station between −2 and < 0 OA 250 (100.0) OP 76 (73.8) OT 96 (100.0) Total 422 (94.0) Station at or below 0 OA 223 (100.0) OP 17 (63.0) OT 20 (100.0) Total 260 (96.3)
OP
OT
Total
P 0.48
1 (3.3) 3 (10.7) 4 (5.1) 8 (5.8)
0 (0.0) 30 0 (0.0) 28 0 (0.0) 79 0 (0.0) 137
0 (0.0) 26 (25.2) 0 (0.0) 26 (5.8)
0 (0.0) 250 1 (1.0) 103 0 (0.0) 96 1 (0.2) 449
0 (0.0) 10 (37.0) 0 (0.0) 10 (3.7)
0 (0.0) 223 0 (0.0) 27 0 (0.0) 20 0 (0.0) 270
0.001
0.001
Data given as n (%) or n. OA, occiput anterior; OP, occiput posterior; OT, occiput transverse. Table 3 Sensitivity, specificity and positive (PPV) and negative (NPV) predictive values of diagnosis of fetal occiput posterior (OP) during labor for OP at delivery, stratified according to fetal head station at intrapartum assessment Fetal head station Above −2 Between −2 and < 0 At or below 0
Sensitivity
Specificity
PPV
NPV
37.5 100 100
80.6 82.0 93.5
10.7 25.5 37.0
95.4 100 100
Data given as %.
an OA position for delivery. In this setting, ultrasound showed that all fetuses in OA or OT from station −2 and lower delivered in OA. Moreover, all neonates delivered in OP were already in OP from station −2 and lower. Our study is the first to correlate fetal head position and station during labor, determined by an ultrasound-based device (the LaborPro system), with position at delivery. Hence, because measurements of station and position are automatic or semi-automatic, the data collected are more objective than when position and station are assessed only by ultrasound or vaginal examination. We were able to study a large population, which is important when considering that delivery in OP is relatively rare. Finally, data were collected prospectively in the four centers and fetal head position was therefore assessed even when delivery was performed by Cesarean section. Care providers were not blinded to data provided by the ultrasound-based system, but because the main criterion studied was not the mode of delivery but head position at delivery, this should not influence our conclusions. Our data differ from those of other series in the literature, but most of these other series have used different methodology. Studies of ultrasound assessment of fetal head position in the literature have mostly used either first/second stage1,2,6 or cervical dilatation assessed clinically5,8 as a labor-progression scale. Although there
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OP in labor deliver in OA is a relationship between cervical dilatation assessed clinically and fetal head station assessed by ultrasound9 , we have provided data using fetal head station itself as a labor progression scale. The mechanism leading to OP at delivery is a matter of debate. Gardberg et al. reported that most deliveries in OP were from fetuses in OA during labor1 . This contrasts with data from other authors2,8 and our data. Akmal et al.5 and Souka et al.6 reached different conclusions from Gardberg et al.1 , claiming that the vast majority of cases of OP position at delivery are a consequence of persistence of this position during labor rather than malrotation from an initial OA or OT position5,6 . It seems therefore that OP at delivery results from an absence of rotation from an initial OP position, at least from station −2 and lower. Having the information that the fetal head position is in OP during labor is important. First, it should not influence labor management until late into labor because the vast majority of cases will rotate to OA. Second, it may explain why trials using maternal positioning in labor with fetuses in OP did not show significant improvement after this intervention10,11 . In conclusion, we found that 100% of cases of OP position at delivery were already in OP at station −2 and below. We did not observe rotation from a non-OP to 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.
DISCLOSURE Dr Yoav Paltieli is a senior physician of the OB/GYN Department in Bnai Zion Medical Center, Haifa, Israel,
Copyright © 2015 ISUOG. Published by John Wiley & Sons Ltd.
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and an officer of Trig Medical Inc., Nesher, Israel, the manufacturer of the LaborPro System. The LaborPro Systems were provided by the manufacturer for use in this study.
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