Never heard of that...
Unless it's what happened to me.
I was at a routine checkup and heard the nurse say "it's half/half." I asked "whats half/half, whats that mean" (cuz I jus knew I had something really bad) and she said "your urine, but its ok, we'll just get blood" (which ended up being my #2 kid).
I hadn't missed a period and they had to induce me in the end so that half/half test was VERY SOON after conception.