Research
Obstetrics
Determination of fetal head station and position during labor: a new technique that combines ultrasound and a position-tracking system

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Objective

The purpose of this study was to compare the ultrasound-based LaborPro (Trig Medical Ltd, Yokneam, Israel) system determination of fetal head station and position with routine vaginal examination.

Study Design

This prospective study, which was conducted in 3 centers included 311 measurements that were performed in 166 singleton term pregnancies during the active phase of vertex, uncomplicated labor. Ultrasound-based position-tracking system calculations of fetal head station and position were compared with routine vaginal examination measurements.

Results

Comparison of vaginal examination with the system head station results revealed a mean absolute difference of 5.5 ± 6.1 mm (n = 311). Vaginal examination head-position evaluation, within a 45° interval, complied with the system in 35 of 87 cases (40.2%).

Conclusion

Our data show that an ultrasound-based system can determine fetal head station and position during labor, when compared with vaginal examination, and requires minimal ultrasound skills. The limits of vaginal examination assessment of the head position are in agreement with published data.

Section snippets

System characteristics

The LaborPro system (Trig Medical Ltd, Yokneam, Israel) uses magnetic position trackers and ultrasound technology that are controlled by personal computer-based software. A low-power magnetic field is generated by a flat transmitter (microBIRD-SA; Ascension Technology, Inc, Burlington, VT) that is placed under the mattress of the delivery bed. Three miniature position (1.3-mm diameter) sensors sense the magnetic field that is created by the transmitter, and the system controller calculates the

Fetal head station

The 3 different modes of fetal head station evaluation by the system showed an average absolute difference of 3.5 mm (95% CI, 2.1-4.9 mm) with the BPD plane, 5.8 mm (95% CI, 5.1-6.5 mm) with the IP-Tip, and 6.1 mm (95% CI, 4.9-8.1 mm) with the ABD-Tip (Table 1). The upper 95% CI for the absolute difference does not exceed 8.1 mm for any of the methods. Mean differences and mean absolute difference, which were obtained from the 3 sites, were comparable (P = .655 and .387, respectively).

Analysis

Comment

This study demonstrates that an ultrasound- and position sensing-based system can determine fetal head station and position during labor when compared with vaginal examination, even in the hands of a nonskilled ultrasound operator. Fetal head station evaluation by the BPD-plane and IP-Tip mode gives the closest results to vaginal examination.

The system that we evaluated was reliable in all stations that were tested with its different modes of measurements. It required very little ultrasound

Acknowledgments

We thank Diane Nicholson, CNM, and the Maimonides Medical Center delivery ward midwifes; Orna Caspin, RN, Ms Ayelt Kravezki, Rina Shachar, RN, and the Bnai Zion Medical Center delivery ward midwifes; and Fanny Revel, Fabienne Boirot, and the CHI Poissy-Saint-Germain-en-Laye delivery ward midwives for their time and proficiency.

References (10)

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Cited by (0)

Authorship and contribution to the article is limited to the 7 authors indicated. There was no outside funding or technical assistance with the production of this article.

Cite this article as: Nizard J, Haberman S, Paltieli Y, et al. 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.e1-404.e5.

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