Untucked unisex scrubs are not proper OR attire. You don't enter my OR with scrubs untucked as that violates my standard scrub policy. Contrary to popular belief, scrubs are worn to prevent release of skin particles and hair into the environment of the OR. An untucked scrub suit is not able to accomplish this.
If your scrub suit is tunic (nurses scrubs)you can wear it untucked (note that tunic tops are much longer than unisex scrub tops). If it is not, the top should be tucked into the pants to prevent contact with sterile surfaces. The ties should be tucked in before you step up to the scrub sink too. Scrubs should be made of lint-free material, fit properly (not too tight as this causes chafing of skin) and clean. When outside of the OR, a lab coat is worn over them.
If you sleep in scrubs at home, you cannot wear those into the hospital OR. If you wear scrubs in, you change before you start your first case and change between cases if your scrubs become soiled. You also change scrubs between cases if they become soiled with body fluids. If body fluids soak through to your underwear, you change those too.
If you are a non-sterile person (anesthesia or circulator) you are required to wear a cover jacket over either tunic or tucked scrub suit to prevent shedding of skin and hair from arms.