Can sonographic depiction of fetal head position prior to or at the onset of labor predict mode of delivery?

Impact of ultrasound guided training in the diagnosis of the fetal head position during labor: A prospective observational study

OBJECTIVES

To assess whether the additional training with transabdominal ultrasound may improve the accuracy of the transvaginal digital examination in the assessment of the fetal head position during the active stage of labor.

METHODS

Prospective observational study involving 2 residents in their 1 st year of training in Obstetrics with no prior experience in neither transvaginal digital examination nor ultrasound. Women with term, cephalic presenting fetus and active labor with cervical dilation ≥ 8 cm and ruptured membranes were included. In the preliminary phase of the study, the resident A ("blinded") was assigned to assess the fetal head position by transvaginal digital examination, while the resident B ("unmasked") performed transvaginal digital examination following transabdominal ultrasound, which was considered to be the gold standard to determine the fetal head position. After 50 examinations independently performed by each resident in the training phase, a post-training phase of the study was carried out to compare the accuracy of each resident in the diagnosis of fetal head position by digital assessment. The occiput position was eventually confirmed by ultrasound performed by the main investigator.

RESULTS

Over a 6 months period, 90 post-training vaginal examinations were performed by each resident. The number of incorrect diagnoses of head position was higher for the "blinded" resident compared with the "unmasked" resident subjected to the ultrasound training (28/90 or 31.1 % vs 15/90 or 16.7 % p = 0.02). For both residents a wrong diagnosis was more likely with non-OA vs OA fetuses but this difference was statistically significant for the "blinded" Resident (10/20 or 50 % vs 18/70 or 25.7 % p = 0.039) but not for the "unmasked" Resident (5/18 or 27.9 % vs 10/72 or 13.9 % p = 0.16).

CONCLUSION

The addition of transabdominal ultrasound as a training tool in the determination of the fetal head position during labor seems to improve the accuracy of the transvaginal digital examination in unexperienced residents.

Association of fetal biparietal diameter with mode of delivery and perinatal outcome

OBJECTIVE

To determine the association between sonographic assessment of fetal biparietal diameter (BPD) and pregnancy outcome.

METHODS

This was a retrospective cohort study of pregnancies at 37-42 weeks of gestation which had antepartum sonographic measurement of BPD within 7 days before delivery. Eligibility was limited to singleton pregnancies with neither known structural or chromosomal abnormalities nor prelabor Cesarean delivery (CD). The association of BPD with outcome was analyzed using multivariate logistic regression, receiver-operating characteristics curves and stratification according to BPD quartiles.

RESULTS

In total, 3229 women were eligible for analysis, of whom 2483 (76.9%) had a spontaneous vaginal delivery (SVD), 418 (12.9%) underwent operative vaginal delivery (OVD) and 328 (10.2%) underwent CD. The mean BPD in the obstetric intervention groups (OVD and CD) was significantly higher than that in the SVD group (P < 0.001). After adjusting for confounders, increased BPD was an independent risk factor such that higher values of BPD were associated with progressively higher risk of obstetric intervention (adjusted odds ratio, 1.05 for each 1-mm increase in BPD (95% CI, 1.02-1.09)), but no clear cut-off value for obstetric intervention was found. The fourth quartile group (BPD ≥ 97 mm) was associated with a significantly lower SVD rate (P < 0.001) and higher OVD rate (P = 0.04), relative to the first (BPD 88-90 mm) and second (BPD 91-93 mm) quartile groups, with no apparent adverse impact on immediate neonatal outcome.

CONCLUSIONS

Increased BPD within the week prior to delivery is an independent risk factor such that higher values of BPD are associated with progressively higher risk of obstetric intervention; however, in our experience, no adverse neonatal outcome resulted from such intervention. Thus, increased BPD should not discourage a trial of vaginal delivery.

Fetal head-symphysis distance: a simple and reliable ultrasound index of fetal head station in labor

OBJECTIVES

To assess the reproducibility of measurement of a new sonographic index of fetal head station in labor, the fetal head-symphysis distance (HSD), using three-dimensional ultrasound, and its correlation with digital assessment of fetal head descent and with the angle of progression (AoP).

METHODS

Three-dimensional (3D) ultrasound volumes were acquired from 47 nulliparous women in active labor following assessment of fetal head station with digital examination. The HSD (the distance between the lower edge of the pubic symphysis and the nearest point of the fetal skull) was measured independently by two operators in order to evaluate intra- and interobserver reproducibility. The correlation between HSD, AoP and fetal head station was evaluated using regression analysis. Using 3D tomographic ultrasound imaging (TUI), measurements of the HSD were obtained in different parasagittal planes to evaluate the influence of inaccurate alignment of the probe with the midline of the pelvis.

RESULTS

Measurement of HSD showed high intraobserver (intraclass correlation coefficient (ICC) = 0.995; 95% CI, 0.991-0.997) and interobserver (ICC = 0.991; 95% CI, 0.984-0.995) reliability. In addition, a high correlation was demonstrated between mid-sagittal and parasagittal HSD measurements. HSD showed significant negative correlation with both fetal head station and AoP.

CONCLUSION

Fetal HSD is a simple and reliable method for the assessment of fetal head descent in labor.