Criteria: Inclusion Criteria:  18-40 years Primipara or multipara Singleton pregnancy ≥ 37 weeks American Society of Anesthesiologists physical status classification I to II Scheduled for elective cesarean section under spinal anesthesia  Exclusion Criteria:  Body height < 150 cm Body weight > 100 kg or body mass index (BMI) ≥ 40 kg/m2 Eclampsia or chronic hypertension or baseline blood pressure ≥ 160mmHg Hemoglobin < 7g/dl Coagulation or renal function disorders Known allergy to hydroxyethyl starch Fetal distress, or known fetal developmental anomaly