Picking a breast pump: vacuum considerations

What do I need to know about picking a breast pump? Suction/Vaccum


You would think that a stronger breast pump is better. But before you put that breast pump on the highest setting, make sure you know the benefits (and risks) of using the highest strength setting. Breast Pump power of suction is usually documented as mmHG which is millimeters of mercury, the standard unit of measuring vacuum pressure. Studies were done on babies sucking at the breast and breasts pump suction levels are based off what we know of how babies remove milk from the breast. The suction level, or vacuum, is DIFFERENT than the cycle speed, which is how fast it pumps. This is why breast pumps should have two settings that should be changeable: cycle (speed) and vacuum (strength). Most pumps will cycle 40-70 cycles per minute. This is based off of the average number of sucks a baby does at the breast in that same amount of time.


Breast pump effectiveness is evaluated by measuring the vacuum (also called suction) of the pump with a pressure gauge, an instrument that measures negative pressure. The gauge needle points to a number from 0 to 450 mmHg (the abbreviation for millimeters of mercury – Hg is the chemical symbol for mercury).  The gauge measures the vacuum, not the speed, of the pump. When there are questions about a pump’s performance, the concern is usually about the vacuum, but not always. Each breast pump has been manufactured to have specific pressures based off that unique pump. When assessing different pumps, the reading on the gauge is then compared to a standard range for that individual breast pump that is being tested, to determine whether the pump is performing per manufacturer’s guidelines or not. When you purchase a breast pump, the mmHg the pump has a capacity to reach may be in the product listing or manual. This number is important to pay attention to. Based on known research for the vacuum babies can generate a that the breast to remove milk, the pressure leves should be in the range of 220 to 350. The number is the maximum suction level that specific pump can achieve. “Hospital grade” pumps generally have maximum suction levels in the 300 range while personal grade pumps are generally in the 200 range. This doesn’t necessarily make a pump better or worse. Hospital grade pumps typically have bigger, stronger motors as they are physically bigger pumps. They are also multi-user pumps that need to have a longer shelf life for use.

Interestingly enough, vacuum levels can vary based on weather (so do not test pumps during stormy conditions) and elevation. Maximum pump vacuum values are set at sea level. The higher you are in elevation, the lower the maximum suction strength your vacuum with achieve!

Breast pump suction is supposed to mimic baby's natural sucking through several phases:

  • Let Down - mimics when baby is vigorously sucking at the very beginning of the feeding and in order to try to stimulate additional let downs during the feeding. Babies can trigger any where from 2-9 let downs in a feeding. This phase stimulates the nerves in your nipples, which signals the release oxytocin, the hormone responsible for letting down your milk. The release of oxytocin contracts the small muscles that surround your milk-producing tissue, which squeezes milk into your ducts and down to the nipple which is then removed by the baby. Many babies will stay in this vigorous sucking phase for up to 1-2 minutes or until they trigger your let down.
  • Expression - this phase is when baby's sucking slows down, and he/she is swallowing the remove all the milk that was let down from the breast. Many babies stay in this phase for 4-8 minutes, the time it takes to “reset” your hormones to trigger another hormone release of oxytocin.

Vacuum suction patterns have been programmed into certain pumps that copy the movements of an infant's tongue with the goal of to reproducing the pattern of how older infants suck. After the first few weeks, babies will typically alternate between a light and fast "flutter sucking" to a deep and rhythmic sucking pattern, and occasionally when flow changes suck with both intensity and speed. By alternating back and forth between similar patterns on the pump, more let downs can be triggered which allows more milk to be expressed.  Pumping with higher strength and efficiency is what is needed to make sure that the body receives adequate signals to increase breast milk volume and to transition from colostrum to mature milk when establishing supply in the immediate days postpartum. This is especially imperative in situations where the pump is replacing direct breastfeeding. This happens when there is a separation from mother and baby in the first week after birth, baby is unable to latch and suck adequately, there is a tongue tie and the family is waiting to have that released, or any other reason why a parent would choose to exclusively pump.

It’s not true that higher pump suction level equals more milk output. The highest suction level on a breast pump are actually above the comfort zone of the majority of pumping mothers. So even if the breast pump has a maximum suction level of 350 mmHg, most will still feel more comfortable expressing in the range of 150 – 200 mmHg regardless of whether the pump can reach 250 or 350 mmHg at its maximum setting. Pumping at too high of a suction level can actually hinder milk flow and even be the root cause of plugged ducts, mastitis, and breast/nipple damage! Think of it like drinking from a juice box straw. With hard sucking, the juice box starts to collapse on itself and not as much juice can move out because of the vacuum effect. You get more juice by gentle, consistent sucking. Milk ducts are small, compressible tubes inside the breast that move milk from milk-making glands at the back called alveoli down to every smaller diameter ducts that empty to nipple pores at the front. Too much breast pump suction compresses the areolar tissues which squeezes the ducts and actually decreases the flow of milk out the ducts. With time this can cause milk to back up in the breast, increasing the risk of plugged ducts. This can also foster inflammation and risk damage.

So why do you feel like you need to turn the pump suction all the way up to move your milk? The number one reason I see for this is because you’re actually using the wrong side flange/breast shield. The majority of people cannot pump with the flange that comes in the box. The 24mm flange was standardized many years ago and hasn’t changed much with time.  In my experience, the majority of the people I work with need to size DOWN, and often significantly. When the flange is too big there is too much air space in the tunnel and a higher vacuum level is needed to generate enough change in the negative pressure in the flange to move the breast tissue. By finding the correct flange fit, less vacuum is needed to effectively move milk and the entire pumping experience is more comfortable.

It’s impossible to know ahead of time which cycle and suction settings will work best for your when you start using a breast pump. Everyone’s anatomy is unique and their sensitivity to the pump is individual. What works for one person may not necessarily work for the next. Those with nipple sensitivity may need a softer, gentler pump that cycles slower and with less vacuum. Other many have larger breasts with longer nerve pathways from the nipple that need higher suction and speed to stimulate let down.  When considering a breast pump, the most important thing is having a pump that gives you the most flexibility to adjust cycle and vacuum settings to find what works to trigger your milk.

If you’re buying a hospital grade breast pump because you know you’re going to be frequently pumping at work or exclusively pumping, look for a maximum vacuum strength above 300 mmHg. Most hospital grade breast pumps on the market will top out at 320 – 350 mmHg. If a breast pump is marketed as hospital grade and the maximum suction level is listed at below 300 mmHg, you should look more closely at the technical specifications and compare them to other hospital grade breast pumps on the market before buying it. If you’re buying a personal grade breast pump, look for a maximum breast pump suction level of 250 – 300 mmHg. The majority of personal grade electric breast pumps on the market fall within this range. If the vacuum strength tops out at below 250 mmHg, it usually means a weaker motor. This may still stimulate a small percentage of pumpers, especially in the early days postpartum when it is easiest to trigger let downs, but may not be strong enough for long term pumping. You should look more closely at the technical specifications before buying a breast pump like this, because a weaker motor means the motor has to work harder to perform at the same level as other personal grade breast pumps. These pumps also wear out faster and the motors don’t work as well for as long.