I truly wish I had known about this the first time I breastfed. I always felt like my pump never fit quite right, but I now realize my flanges were slightly too large and likely impacted my comfort and pumping experience.I highly recommend purchasing this sizer and measuring toward the end of pregnancy, since sizing can change throughout pregnancy and postpartum. I also recommend rechecking your size after birth to ensure you have the best possible fit once your milk comes in.Im so glad I saw an influencer recommend this tool its such a simple thing that can make a huge difference, and I wish more new moms knew about it before starting their breastfeeding journey.