First time buyer- at loss for leggings sizing

Hi, I have never tried lulu leggings but have always heard great things. I am 11 weeks pregnant and finally decided to invest in them in hopes I can wear them during pregnancy and after. I went by the sizing and just ordered Align in size 18 and Wunder Train leggings in size 20. I measure 53 in hips and 44 in waist right now. This is second pregnancy so inches are piling up quicker. Pre pregnancy I was wearing either L or XL in leggings or pants. Currently wearing 1X in other brands like Popflex or target with some room to grow. My problem is see that I now see youtube videos where in ladies bigger than me are wearing size 12 or 14 in leggings. Few mentioned that size 20 accomodates upto size 26 28, what??? With the sizes I ordered I may be comfy during pregnancy but I do not want them to be too big that they slide down postpartum. How does the sizing go? Is sizing chart even accurate?