I'm also having a second one as baby measures just below 90th centile at 28 week scan so said I'd rather do it now then wait until 32 weeks and do it then I had it twice with my 1st and both came back negative
I had the test for the first time at 31 weeks and it came back positive. Managing it with diet for now (36 weeks), and I’m getting the hang of it. If it does come back positive brace yourself for them wanting to induce at 39 weeks.
I had to have a second one late on as baby was measuring really big. It was still negative for me, but you can develop it at any point in pregnancy. Hope it goes ok for you xx