You are a PA working in GP and you have a 30 year old patient who is in her third trimester. She has come in complaining of swollen feet, ankles, legs and fingers. Upon examining the patient you note 2cm of oedema up to her calf. Her observations are as follows; BP 165/100, tempurature 37 degrees, 99% O2, RR 17 breaths per minute, HR 80 bpm. What is the first investigation you will conduct?