The goal of this clinical trial is to learn which method of intravenous fluid works better for treating abnormal fetal heart rate patterns during labour in low-risk pregnant women at term. The main question it aims to answer is:

Does a rapid fluid bolus (500 mL given quickly) convert abnormal fetal heart rate tracings to normal within 30 minutes better than slow continuous infusion? Researchers will compare a 500 mL normal saline bolus followed by continuous infusion to continuous infusion alone to see which method improves fetal heart rate patterns faster.

Participants will:

• Be placed in the left lateral position and receive supplemental oxygen by face mask
• Have oxytocin stopped if it is being given
• Receive normal saline through an IV line - either as a rapid bolus or a slow continuous drip, depending on which group they are assigned to
• Have fetal heart rate monitored continuously and assessed at 30, 60, and 120 minutes
• Have blood pressure, heart rate, and oxygen levels checked every 15 minutes
• Have two ultrasound measurements taken - one of a vein in the abdomen and one of blood flow in the umbilical cord - at the start and at 30 minutes

Intravenous fluid is a key component of intrauterine resuscitation (IUR) for Category II fetal heart rate tracings. However, no randomised trial has compared bolus versus continuous infusion directly.

Intervention :

Both groups receive normal saline from a 1000 mL bag through a 21-gauge cannula. The bolus group receives the first 500 mL as a rapid free-flow infusion (IV bag positioned 110 cm above hand level), followed by the remaining 500 mL at 150 mL/h. The continuous group receives the full 1000 mL at 150 mL/h throughout. All participants also receive standard IUR: left lateral positioning, oxytocin discontinuation where applicable, and supplemental oxygen 10 L/min by face mask.

Outcome Assessment :

The primary outcome (EFM category at 30 minutes) is assessed by the attending physician from a separate room, blinded to group allocation. All EFM tracings are also independently re-adjudicated by two blinded reviewers after delivery.

Physiological Surrogates :

A single trained operator measures inferior vena cava collapsibility index (IVC-CI) by M-mode ultrasound and umbilical artery Doppler pulsatility index (UA PI) at baseline and 30 minutes to assess maternal volume status and fetoplacental resistance.

Statistical Analysis :

The primary analysis uses Fisher's exact test with risk difference, relative risk, and number needed to treat. Cumulative recovery is modelled by discrete-time survival analysis. A pre-specified BMI subgroup analysis and blinded re-adjudication sensitivity analysis are included.

Inclusion Criteria:

1. Singleton
2. Thai nationality
3. Gestational Age more than equal 37 Weeks
4. Maternal Age 20-35 Years
5. Cephalic Presentation
6. Electronic Fetal Monitoring (EFM) Category II

Exclusion Criteria:

1. Maternal underlying diseases : Cardiac disease, Pulmonary disease), Overt DM, Thyroid disease,. etc
2. High risk pregnancy :Pre-eclampsia/Eclampsia), GDM
3. Fetal abnormalities
4. Maternal receiving medications for example : Magnesium sulfate, Pethidine, Opioids
5. Oligohydramnios

Data was saved in form of Microsoft excel spreadsheet and SPSS file

Participants were not informed of their group assignment. The attending physician who assessed EFM tracings at 30 minutes did so from a separate room without knowledge of treatment allocation. Two independent reviewers re-adjudicated all EFM tracings after delivery, blinded to allocation, real-time classification, and each other's assessments. The statistician received a locked dataset with coded group labels (A and B) and performed all analyses prior to unblinding. The resident and bedside nurse who administered the fluid were aware of the assigned infusion regimen and were not blinded.