ObjectiveTo define reference values of the patellar reflex in normotensive pregnant and postpartum women and to compare these with values in women with preeclampsia. DesignObservational study. SettingUniversity teaching hospital in the Netherlands. PopulationNormotensive non-pregnant women, pregnant women and preeclamptic women. MethodsIn normotensive pregnant women the patellar reflex was cross-sectionally recorded using surface electromyography at four time points during pregnancy and six to eight weeks postpartum. In non-pregnant normotensive women this was recorded once. Preeclamptic women were recorded during pregnancy and postpartum. Main outcome measuresLatency and amplitude of the compound muscle action potential of the patellar reflex. ResultsLatency and amplitude of the compound muscle action potential during normotensive pregnancies showed no changes compared with the non-pregnant state during reproductive age. Latency of the compound muscle action potential was increased in pregnancies with severe preeclampsia compared with normotensive pregnancies. These differences disappeared postpartum. ConclusionsDuring pregnancy, the patellar reflex can be assessed using surface electromyography. Latency and amplitude show no changes during normotensive pregnancies and are no different from the postpartum or non-pregnant values. In severely preeclamptic women, latency is increased. The clinical value of this is limited.