Flange Fit

01

Measuring Your Nipple

​Measure your nipple diameter before pumping or feeding—when swelling is at its lowest—for the most accurate resting size. Ideally, test fit before a latch or at least one hour after feeding or pumping.

Nipples typically expand by 2–3 mm in diameter and length during a pumping session. Use your resting size as a baseline:​

• Add 4 mm if you’re measuring on your own

• If you’re working with a lactation consultant, she will fit closer

Note that nipples often appear slightly wider horizontally—measure both directions and round up if needed.

Testing the Fit

Flange fit also depends on your breast tissue, skin elasticity, and any swelling (edema). Always test during an actual pumping session, using the expression phase (not the fast initial rhythm), and set your pump to your maximum comfortable vacuum (MCV)—the highest suction that feels strong but not painful. This level typically matches your baby’s natural suction.

During testing (minimum 5 minutes of active pumping), observe:

• Nipple is centered and moves freely in the tunnel

• Minimal areola is pulled into the tunnel

• No rubbing, friction, or discomfort

• Flange stays comfortably in place without excess pressure

A small amount of nipple balm or lubricant may be helpful to reduce friction during testing, though it’s not always needed.

For wearable pumps, alignment is key—make sure nipples are centered and check each breast individually.

Why it Matters

The right fit increases comfort and milk flow, supports milk supply, helps prevent nipple damage and clogged ducts. The wrong fit can decrease milk output, cause soreness, cracking, bruising, compress milk ducts, restricting flow.Too small = friction, pain, and potential injury; Too large = less suction and excess areola pulled in. Even mild pressure on the breast can reduce milk flow. During milk ejection, ducts expand up to 68%—compression can collapse them and block milk release. When to Reassess: Early postpartum (due to swelling and IV fluids, After receiving IV fluids during delivery, If exclusively pumping or using NICU pumping plans, Anytime pain, nipple changes, or milk output issues arise.