Breast shields vary in size. They are measured by the width of the barrel opening. Most pumps supply 24-millimetre breast shields, but other sizes are usually available. Common sizes are 21-mm, 24-mm, 27-mm, 30-mm, and 36-mm.
It is very important to have the correct size of shield to allow the nipple to move forward and backward in the shield without pain and to allow only a small portion of the areola and tissue underneath (the nipple root) into the barrel.
While most mothers find the 24-mm size effective, others may need to use a different size. The size can also change with time (Jones 2009). A small number of mothers may need a different breast shield size for each nipple.
1) Correct breast shield size
Mothers can estimate the best shield size by measuring the width of the nipple where it meets the areola (the nipple bottom). Choose the shield size that is closest to the size of the nipple bottom and is at least two millimeters wider than the nipple bottom.
If your breast shield size is correct, you should expect:
- No nipple pain or damage.
- To obtain the expected amounts of milk.
- Pumping one breast to take a maximum of 20 minutes.
- For the breast to feel completely softened after pumping.
2) Breast shields that are too large
If the breast shield is too big, the nipple travels too far down the barrel, which can result in pain and reduced milk flow from:
- Excessive stretching of the nipple root.
- Excessive stretching of the milk ducts inside the nipple root.
- Swelling of the nipple root.
Noise can be a sign that the shield is too big and is losing suction, allowing air to enter.
3) Breast shields that are too small
If the breast shield is too narrow, the nipple scrapes along the sides of the barrel. You may notice dead skin in the barrel. If it is much too small, the nipple may not even be able to enter the barrel.
Breast shields that are too small can cause:
- Pain and injury to the nipple sides and bottom.
- Swelling of the nipple.
- Poor milk flow.