To have a smoother pumping experience, having a flange that fits nicely onto your nipple will help prevent some unnecessary discomfort/pain.
We recommend that you measure your nipple nearer to due date, or in the last trimester as nipple size may change. It may also change during the course of breastfeeding.
You can use a ruler to measure the diamater, add 2-3mm to the nearest available flange size. That is the general guide on the size to use. Alternatively, you can download our printable nipple ruler here or head down to any of our retailer to obtain 1.