Currently there is no guideline to decide on the most appropriate dose of spinal anaesthesia. This study is planned to find out factors that influence the effect of spinal anaesthesia in pregnant mother going for Caesarean section and both the mother and baby's outcomes. Investigators will recruit pregnant mothers who are planned for elective Caesarean section under spinal anaesthesia at University Malaya Medical Centre before operation and obtained their consent to participate in this study. Routine standard care will be provided for all the participants. Perioperative data including vertebral column length and abdominal girth measured by measuring tape will be collected and analysed. There is no new intervention performed on participants.

The rising rate of caesarean section is a global phenomenon. Rate of caesarean section in Malaysia were 23.41% in 2011 and 25.08% in 2012. Subarachnoid block is the preferred anaesthetic technique for most lower segment caesarean section as compared to general anaesthesia. This is because general anaesthesia is associated with higher risk of failed endotracheal intubation and aspiration of gastric contents in parturients. Moreover, usage of pencil-point spinal needle had reduced the risk of postdural puncture headache frequency and severity.

Effective surgical anaesthesia is the main objective of subarachnoid block. Therefore, adequate sensory blockade with minimal maternal and neonate side effects are warranted. The suitable level of sensory blockade post subarachnoid block for lower segment caesarean section is bilateral block up to T6 dermatome level to pinprick. This will block the somatic sensation and eliminate the visceral pain from peritoneal manipulation during caesarean section.

However, the spread of subarachnoid block may be variable. Various patient variables such as age, height, weight, body mass index, vertebral column length and abdominal girth influence the spread of subarachnoid block. Inadequate sensory blockade will cause parturient suffer from pain while excessive blockade will lead to unwanted sympathetic inhibition causing hypotension and bradycardia. Ability of an anaesthetist to determine optimal dose to achieve adequate level of sensory blockade yet with minimal unwanted side effects is crucial.

Incidence of maternal hypotension is related to the level of sensory blockade after subarachnoid block.And maternal hypotension is associated with maternal discomfort during caesarean section and poorer fetal outcomes. Therefore, this study is carried out to investigate whether vertebral column length and abdominal circumference affecting the spread of intrathecal hyperbaric bupivacaine in term parturient.

Previous studies showed conflicting results on the factors that influence the effect of spinal anaesthesia. One of the studies was carried out in China which might not reflect the investigator's local multiracial population characteristics. Previous studies also did not investigate the outcome of baby related to maternal hypotension which is known complication.

Inclusion Criteria:

• patients aged more than 18 years old
• American Society of Anesthesiologists (ASA) physical status I-II
• singleton pregnancy
• gestational age 37 weeks or more
• height 150-175cm and weight 50-100kg

Exclusion Criteria:

• patients with contraindication to subarachnoid block
• history of allergy to local anaesthetics
• contraindication to NSAIDS use
• failure of subarachnoid block
• any abnormality of spine
• history of spinal surgery
• refusal to participate in this research

all term parturients going for elective Caesarean section

term parturients who are scheduled for elective Caesarean section under spinal anaesthesia in University Malaya Medical Centre