Recently I have taken a ultrasound (normal, as not getting periods from 2 months) ,all beta hcg n hpt are negative ,they told me to not to pee and withhold till you can manage, but I drink around 600 ml water, my bladder was almost full that if I drink furthermore I could vomit, want to go for urine but not that much i.e not in very hurry to pee, but yes I wanted to pee, does ultrasound be accurate.