The first thing you should know as you begin to learn about pumping is know that there are many different sizes of flanges for your nipple. You must also remember that your nipple size can change at anytime during your breastfeeding and or pumping journey.
The first thing to know if the shield or flange you have is correct will be to place your nipple into the flange directly in the center.
Know that when you turn on your breasts pump that your nipple should be able to move freely in and out without irritation.
Avoid gaps and or trapped air between the flange and your breasts to avoid having pain while pumping.
For best results, keep your nipple centered because if not you mat experience nipple damanged, pain or may affect emptying of your breasts.
You can use a small amount of coconut oil to allow your breasts to move freely while pumping to increase your comfort.
How do you know if your flange size is too big?
A flange that is too big will pull too much breasts tissue into the shaft causing pain on your nipple and Areola. Sensation of pulling pain, little or slow express with a need to hand express after pumping.
If you have a gap or air in between this will create a poor suction to get the milk out of your breasts.
If you have large breasts that DOES NOT mean you need a larger flange size! It is key to look at the size of the nipple. Its important to check while pumping as stated above because your nipple can change the shape and form while pumping .
If you have flat or inverted nipples your nipple can change. You will feel pain and less milk will be pumped if you have the incorrect flange size.
How to know if your flange size is too small?
Painful rubbing of your nipple in the flange, you will have nipple trauma from excessive rubbing, your nipple not moving freely in the flange, little milk is being expressed and you may have a milk blister, or clot on your nipple!
Once your supply has regulated you may need to change your flange size due to less inflammation in the breasts from your beginning stages of pumping. Some women may need a different flange size for each breasts.
There are 4 main sizes of flanges that you can consider using:
21mm, 24mm, 27mm, 30mm, 36mm
How to measure your breasts for potential sizes are as follow:
Using a ruler or measuring tape, measure the diameter of your nipple at the base (across the middle) in millimeters (mm). 1 cm = 10 mm.
Below is a picture of a nipple that has used too large of a flange size causing blisters and clots on the nipple.
The second picture is a flange size that is too big for your nipple thus creating friction and pain by pulling your nipple.
I have also added a video from www.medela.us