[Prediction of shoulder dystocia--combining foetal weight estimation by ultrasound and maternal risk factors--a solution for the dilemma?].

BACKGROUND

Although foetal macrosomia is a known risk factor for shoulder dystocia, foetal weight estimation by ultrasound is imprecise.

METHODS

We analysed in a retrospective, single-centre study whether the combination of foetal sonographic parameters and maternal parameters could improve the prediction of foetal macrosomia and whether on the basis of this findings the prediction of shoulder dystocia in foetal macrosomia could be enhanced. Likelihood ratios for sonographic parameters have been assessed and have been used to calculate post-test-probabilities for fetal macrosomia. All vaginal singleton deliveries with cephalic presentation >or=37+0 week of gestation in the period 1994-2005 (n=8 576) have been analysed. Shoulder dystocia has been observed in 136 cases (1.6%).

RESULTS

In multivariate analysis the strongest predictor for shoulder dystocia was foetal macrosomia (>or= 4000 g), odds ratio=4.04 (95% confidence interval 2.71-6.05), next to diabetes 2.43 (1.14-5.17), obesity (BMI >or=30 kg/m (2)) 1.55 (1.02-2.46), and foetal head circumference (>35 cm) 1.51 (1.02-2.24). Foetal sonographic parameters showed likelihood ratios up to 6.93. The accuracy of shoulder dystocia predictions in cases of birth weight >or=4,500 g improved only slightly from 0.2-3.3%.

DISCUSSION: The accuracy of the estimation of foetal macrosomia has been improved by combining ultrasonography with prepartal maternal risk factors.