Why Does a Baby Trigger Letdown Faster Than a Pump? And What Pumping Moms Can Do to Get Better Results

As a lactation consultant and registered nurse, I hear this question all the time:“Why can my baby trigger letdown so fast, but it takes forever with the pump?”

This is a very real and valid concern for many pumping moms—especially those who are exclusively pumping, returning to work, or building a stash for later use. Understanding why this happens, and what you can do about it, can make your pumping experience far more effective and less frustrating.

Let’s dive into the science behind letdown, what research says about the breast’s response to different types of stimulation, and how you can apply this knowledge in your daily pumping routine.

Understanding the Letdown Reflex

Letdown, or milk ejection reflex (MER), is triggered by the hormone oxytocin. When your baby suckles at the breast, nerve endings in your nipple send a signal to your brain, which causes oxytocin to be released by the posterior pituitary gland. This hormone prompts the myoepithelial cells surrounding the milk-producing alveoli to contract, pushing milk down through the ducts and toward the nipple.

This reflex can be affected by several factors:

• Physical stimulation (baby or pump)

• Emotional state (stress can inhibit oxytocin)

• Hormonal signals

• Conditioning (your body "knows" your baby)

  
  

What the Research Shows: Baby vs. Pump

A key study published in the Journal of Human Lactation in 2003 by Kent et al.¹ measured how different electric breast pump patterns affected milk ejection and milk volume. The researchers used ultrasound to detect when milk ejection occurred and measured how much milk was removed under different conditions.

Key findings from the study:

• Letdown during breastfeeding happened in 56 ± 4 seconds.

• The standard Medela pump pattern (45 cycles/min) triggered letdown in 149 ± 12 seconds.

• Faster stimulation patterns (105–125 cycles/min), designed to mimic a baby’s initial sucking rhythm, reduced letdown time to as low as 104 ± 10 seconds, although this was not statistically significant.

In short: babies are faster and more efficient at triggering letdown than pumps—and for good reason.

Why Is the Baby More Effective?

The baby doesn’t just use suction—they stimulate the breast with warmth, skin contact, pressure, and rhythmic jaw and tongue movements that perfectly coordinate with your body’s oxytocin response.

Not only that—your letdown reflex is conditioned to your baby. You may start leaking just by hearing your baby cry or smelling their skin. A plastic pump simply doesn’t have that same connection.

However, the study found that using faster stimulation patterns that mimic a baby’s non-nutritive sucking at the beginning of a feed (around 105–125 cycles/min) helped reduce the time to letdown during pumping.

Does Suction Strength Help?

Another important finding: Suction strength (vacuum pressure) did not influence how fast letdown occurred.However, once letdown was achieved, a stronger vacuum helped remove more milk, provided it was comfortable for the mom.

In fact, one of the patterns tested (Pattern A, the standard pump rhythm) removed the most milk in the 50–70 seconds after letdown, but took the longest to actually trigger it.

This shows that a strong vacuum can be useful after milk begins to flow, but it’s not the solution if your letdown takes forever.

Do You Always Feel Letdown?

Interestingly, the study found that 21% of milk ejections were not sensed by the mother, even though ultrasound showed that they were happening.

That means if you don’t feel the classic “tingle” or pressure of letdown—don’t panic. Your body might still be working just fine.

How to Use This Knowledge to Improve Pumping

Here are evidence-based tips to make your pumping sessions more effective:

1. Start with a Baby-Like Stimulation Phase

Most babies suck very quickly—up to 120 sucks/min—at the beginning of a feed. If your pump has a letdown or stimulation phase, make sure it runs for the first 1–2 minutes to mimic this rapid rhythm. Use speeds around 105–125 cycles/min if available.

2. Switch to a Slower Expression Mode

Once milk begins to flow or you feel (or suspect) letdown, switch to a slower mode (around 45–60 cycles/min) and increase vacuum only to your comfort level. This phase mimics how babies slow their sucking once milk begins to flow.

3. Let the Pump Run Through at Least One Full Letdown

Try to pump for 15–20 minutes or until the milk flow stops, even if it takes a while for letdown to occur. Some moms benefit from staying on the pump until they feel a second letdown, especially during power pumping or to build a freezer stash.

4. Create a Letdown Routine

Because letdown is partly conditioned, doing the same routine before pumping can help. Examples:

• Look at a picture or video of your baby

• Smell a piece of your baby’s clothing

• Use warmth or massage on your breast

• Pump in the same quiet space each time

5. Don’t Max Out the Suction

Comfort is key. Going above your threshold won’t help letdown and may cause nipple damage. Let the suction work with your body, not against it.

6. Skip the “Pause” Feature

The study also tested a pump pattern that paused regularly to mimic a baby’s pauses while suckling. The result? It removed less milk. Keeping a steady, rhythmic pattern is more effective for milk removal.

My Take as a Lactation Consultant

As someone who’s worked with hundreds of pumping moms, I always emphasize: the pump is not your baby. You might need to work a little harder to trigger letdown—but with the right techniques, your pump can become a powerful tool.

Some moms may benefit from hand expression to trigger letdown first, followed by pumping. Others respond best to warm compresses, nipple stimulation, or even light breast massage.

Most importantly: Don’t compare your pumping output to what your baby gets directly at the breast. Babies are more efficient, and that’s okay. Your pump can still do an amazing job with the right rhythm, suction, and consistency.

Need Personalized Help?

If you’re struggling with:

• Long letdown times

• Low pumping output

• Pain or discomfort with pumping

• Transitioning to exclusive pumping or back to work…you’re not alone.

I offer 1:1 lactation consultations where we’ll go over your pumping routine, evaluate your pump settings, and come up with a plan tailored to you.

I also created a mini pumping guide full of practical tips to help you get more milk and feel more confident.Leave a comment or message me for the link, or find it directly on my website.

References

1. Kent, J. C., Ramsay, D. T., Doherty, D., Larsson, M., & Hartmann, P. E. (2003). Response of breasts to different stimulation patterns of an electric breast pump. Journal of Human Lactation, 19(2), 179–186. https://doi.org/10.1177/0890334403252473

2. Drewett, R. F., & Woolridge, M. W. (1979). Sucking patterns of human infants. Early Human Development, 3(3), 225–240.

3. Woolridge, M. W. (1986). The development of human feeding. In A. Lucas (Ed.), The Biology of Human Milk (pp. 61–85).

4. Ramsay, D. T., Kent, J. C., Owens, R. A., & Hartmann, P. E. (2004). Ultrasound imaging of milk ejection in the breast of lactating women. Pediatrics, 113(2), 361–367.

5. Mitoulas, L. R., Kent, J. C., Cox, D. B., Owens, R. A., Sherriff, J. L., & Hartmann, P. E. (2002). Vacuum profile influences the removal of milk from the breast. Early Human Development, 67(3), 193–207.