The leggings are designed with an expandable belly panel so you can get the most out of them. You don't have to wait to wear them. From as early as week 12,  graduated compression can assist with circulation - your heart needing to work harder to increase blood flow through you to the placenta and your growing baby.TheRY compression leggings are rated at 15-20mmHg and is suitable for all day wear. As with anything though, if at any point you are experiencing discomfort from wearing anything it is best to discontunue wear and seek advise.