Determining the Position of the Fetal Head in the Second Stage of Labor

Abstract & Commentary

Synopsis: The vaginal exam was correct in 71.6% of cases, and the ultrasound was correct in 92% of cases.

Source: Chou MR, et al. Vaginal vs Ultrasound Examination of Fetal Occiput Position During the Second Stage of Labor. Am J Obstet Gynecol. 2004;191:521-524.

A very simple study appeared in the August edition of the American Journal of Obstetrics and Gynecology. It dealt with the ability of clinicians to precisely determine the position of the fetal head in the maternal pelvis during the second stage of labor.

Chou and colleagues studied 88 patients after full dilatation. One clinician was asked to determine the position of the fetal head digitally, and another blinded examiner, using transabdominal and transperineal ultrasound, assessed the fetal position in the same patient shortly before or after the digital examination. The ultrasound clues to determining the position of the fetus were the position of the fetal spine and the alignment in the pelvis of the fetal orbits and occiput. The end point used by Chou et al was the position of the cranium at delivery after restitution.

The vaginal exam was correct in 71.6% of cases, and the ultrasound was correct in 92% of cases. The 3 cases where the ultrasound information was discordant with the delivery results probably involved spontaneous rotation, only 1 of which was directly observed before birth.

Comment by John C. Hobbins, MD

To suggest that super-trained physicians and certified nurse midwives can misdiagnose fetal position at the end of labor represents fighting words. Well unfortunately, there are at least 4 studies showing that vaginal examination is incorrect between 27% and 76% of the time. Once we set aside our defensive responses to this, we should realize that it is not easy to separate a Y from a diamond, or even to accurately determine the direction of the sagittal suture when being confronted with 3-4 cm of caput.

A few studies have pitted clinical exams against ultrasound evaluations in determining fetal position, and have found a major difference. However, in these studies, the gold standard was assumed to be the ultrasound. In this study, Chou et al used a third, and supposedly objective, variable, the position of the fetal head at delivery after restitution.

I suppose we could quibble over the nuances in study design, but it is very clear that ultrasound could become an important, yet simple, adjunct to clinical decision making. For example, Rayburn et al addressed the concept that in patients with dystocia, one might give a little extra time in the second stage if an occiput posterior position was noted on ultrasound. On the other hand, those with occiput anterior or oblique positions would benefit little from further expulsive efforts. Also, the correct application of forceps could be aided by this technique. Very few clinicians can honestly say that they have not delivered a fetus sunny-side up when they thought the fetus was in an occiput anterior position when they applied their forceps.

Every Labor and Delivery floor should have an ultrasound on-site or conveniently available. For transperineal scanning, one can simply use a standard transabdominal curved array transducer housed in a glove, but in most cases, the information can be gained transabdominally.

Also, soon to be published information will be available to help the clinician precisely determine fetal station using transperineal ultrasound. This, in turn, will allow practitioners to truly assess progress in descent.

References

1. Chou MR, et al. Vaginal vs Ultrasound Examination of Fetal Occiput Position During the Second Stage of Labor. Am J Obstet Gynecol. 2004;191:521-524.

2. Rayburn WF, et al. Dystocia In Late Labor: Determining Fetal Position By Clinical and Ultrasonic Techniques. Am J Perinatol 1989;6:316-319.

3. Sherer DM, et al. 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(3):258-263.

4. Sherer DM, et al. 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(3):264-268.

5. Souka AP, et al. Intrapartum Ultrasound for the Examination of the Fetal Head Position in Normal and Obstructed Labor. J Matern Fetal Neonatal Med. 2003;13:59-63.

John C. Hobbins, MD, Professor and Chief of Obstetrics, University of Colorado Health Sciences Center, Denver, is Associate Editor of OB/GYN Clinical Alert.