Hypotension in Threatened Preterm Labour Treating with Initial Loading Dose of 30 mg versus 40 mg Nifedipine

INTERVENTION: Arm 1: nifedipine 30 mg loading in 1 hour (10 mg orally every 20 minutes) then nifedipine slow release (SR) 20 mg orally every 4‐8 hours until 48 hours, regularly of treatment given will be at the discretion of the treating physician CONDITION: hypotension in threatened preterm pregnant who treated with nifedipine PRIMARY OUTCOME: Incidence of hypotension measurement by non invasive measurement instrument,autonomic blood pressure monitor,Dinamap blood pressure monitor have set the standard for accuracy and have been calibrated by schedule and all candidate will use the same instrument and systolic and diastolic blood pressure were recorded in medical recording form. SECONDARY OUTCOME: Nil INCLUSION CRITERIA: Pregnant women with gestational age between 24 to 36 weeks with one or more uterine contractions in 10 minutes with Cervical dilatation 0 to 3 cm