Finger Plethysmography to Predict Fluid Responsiveness in Healthy Pregnancy and Severe Preeclampsia

The goal of this observational study is to determine whether noninvasive finger plethysmographic cardiac output monitoring can help predict fluid responsiveness in pregnant women, including those with preeclampsia with severe features. The main questions it aims to answer are : * Can changes in cardiac output measured by finger plethysmography predict fluid responsiveness? * How does this method perform compared with standard echocardiographic assessment? Participants will provide consent and undergo noninvasive hemodynamic monitoring and a brief reversible physiological challenge.