Aww, I understand the worry, lalo na kapag first time! Brown marks or spots sa pregnancy can be so many things, sometimes it's just hormonal changes, melasma, or even just skin pigmentation shifting because of the hormones, pero syempre need mo talaga i-confirm with your OB para sure kung ano exactly yan at kung kailangan ng treatment. A few of us mums had similar concerns during pregnancy and lahat naman okay lang after the doctor checked, so don't stress yourself too much pero do get it checked soon para peace of mind mo lang!