Ten publications and studies on the relation between maternal height and the risk of dystocia due to cephalopelvic disproportion (CPD) are analysed. The rate of Caesarean sections was chosen as the CPD indicator. When maternal height is presented in percentiles, curves can be superimposed, and sensitivities and specificities of the various studies may be analysed together. One biased study was excluded; the remaining 9 were pooled and regression lines calculated for sensitivity (Se) and specificity (Sp) of the entire set of points. The resulting model, i.e. Se = 10.9+1.99 Y and Sp = 99.9 − 0.99 Y, permits easy calculation of the expected sensitivity and specificity for each percentile Y. When the frequency of Caesarean section due to CPD is known, positive and negative predictive values can also be calculated. The proposed formulas can also be used to determine confidence intervals.
The findings in terms of the sensitivity and specificity of low maternal height as a risk factor for dystocia indicate that 1 out of 5 pregnant women would have to be referred for further investigation to identify half of the cases of mechanical dystocia necessitating Caesarean section. The predictive value for a Caesarean rate of 2% (a value often seen in developing countries) for this 20th percentile would be only 5%. Practical ways of choosing a reference criterion are suggested. A two-track strategy (antenatal check-ups and community monitoring) is proposed.