You should purchase the size that is closest to your pre-pregnancy pant size (pant size 0-8 is a XS/S and pant size 101X is a M/L). If you gained more than 50 pounds during your pregnancy then you should order the next larger size of Shrinkx. IF YOU ARE BETWEEN SIZES the best thing to do is take a measurement of your hips. Measure at the widest part, and if your hips are 40 inches and below we recommend going with the XS/S size. If your hips are over 40 inches, but less than 51.5 inches around, then we recommend going with the M/L size for your best fit.