Abstract: Objective: The purpose of this study was to evaluate if manual muscle testing (MMT) could identify fetal sex in women who did not know the sex of their babies. The null hypothesis was that MMT is no more accurate than chance.Methods: A prospective case series of 27 sequential pregnant patients who did not know the sex of their fetus were included in this study. The examiner was also blind to the sex of the fetus. Manual muscle testing was evaluated after the mother stated “I am having a boy.” Likelihood ratios, specificity, sensitivity, positive predictive value, and negative predictive value were calculated.Results: Fourteen girl babies and 13 boy babies were born. Manual muscle testing accurately predicted the sex 13 times. The positive likelihood ratio was 0.92 (95% confidence interval, 0.42-2.03), sensitivity was 0.40, specificity was 0.54, positive predictive value was 0.46, and negative predictive value was 0.44.Conclusion: Manual muscle testing was no better than chance at predicting fetal sex in this case series.