While breastfeeding has many benefits for a mother and her baby, it has one major drawback: It's incredibly difficult to know how much milk the baby is consuming.
To take the guesswork out of breastfeeding, an interdisciplinary team of engineers, neonatologists and pediatricians at Northwestern University has developed a new wearable device that can provide clinical-grade, continuous monitoring of breast milk consumption.
The unobtrusive device softly and comfortably wraps around the breast of a nursing mother during breastfeeding and wirelessly transmits data to a smartphone or tablet. The mother can then view a live graphical display of how much milk her baby has consumed in real time.
By eliminating uncertainty, the device can provide peace of mind for parents during their baby's first days and weeks. In particular, the new technology could help reduce parental anxiety and improve clinical management of nutrition for vulnerable babies in the neonatal intensive care unit (NICU).
The study will be published on Wednesday (May 14) in the journal Nature Biomedical Engineering. To ensure its accuracy and practicality, the device endured several stages of rigorous assessments, including theoretical modeling, benchtop experiments and testing on a cohort of new mothers in the hospital.
"Knowing exactly how much milk an infant is receiving during breastfeeding has long been a challenge for both parents and healthcare providers," said Northwestern's John A. Rogers , who led the device development. "This technology eliminates that uncertainty, offering a convenient and reliable way to monitor milk intake in real time, whether in the hospital or at home."
"Uncertainty around whether an infant is getting sufficient nutrition can cause stress for families, especially for breastfeeding mothers with preterm infants in the NICU," said Dr. Daniel Robinson , a Northwestern Medicine neonatologist and co-corresponding author of the study. "Currently, only cumbersome ways exist for measuring how much milk a baby has consumed during breastfeeding, such as weighing the baby before and after they have fed. We expect this sensor to be a big advance in lactation support, reducing stress for families and increasing certainty for clinicians as infants make progress with breastfeeding but still need nutritional support. Reducing uncertainty and helping families achieve their breastfeeding goals will lead to healthier children, healthier mothers and healthier communities."
A bioelectronics pioneer, Rogers is the Louis Simpson and Kimberly Querrey Professor of Materials Science and Engineering, Biomedical Engineering and Neurological Surgery at Northwestern — where he has appointments in the McCormick School of Engineering and Feinberg School of Medicine — and the director of the Querrey Simpson Institute for Bioelectronics (QSIB). Robinson is an associate professor of pediatrics at Feinberg and an attending physician in the division of neonatology at Ann & Robert H. Lurie Children's Hospital of Chicago. Rogers and Robinson co-led the study with Dr. Craig Garfield , a professor of pediatrics at Feinberg and attending physician at Lurie Children's, and Dr. Jennifer Wicks , a pediatrician at Lurie Children's.
Three postdoctoral researchers at QSIB contributed equally to the project, each of whom is now a faculty member in Korea: Jiyhe Kim, an assistant professor at Ajou University, led the device design and supported clinical trials; Seyong Oh, an assistant professor at Hanyang University, engineered the wireless electronics; and Jae-Young Yoo, an assistant professor at Sungkyunkwan University, developed methods for data analytics. Kim and Oh are co-first authors with Raudel Avila , an assistant professor of mechanical engineering at Rice University and Northwestern Ph.D. graduate, who led the computational modeling.
Addressing an unmet need
The project started four years ago, when neonatologists and pediatricians at Lurie Children's approached Rogers' team with a critical unmet need. Because the transfer of milk from mother to baby during breastfeeding is not visible and the flow of milk varies, it's nearly impossible to know the precise volume of milk a baby consumes in one sitting.
"Currently, there are no reliable ways to know how much babies are eating when they are breastfeeding," said Wicks, who is a mother of three. "Some pediatricians and lactation consultants will use scales to weigh a baby before and after feeding, and that measurement gives a decent estimate of the amount of milk the baby drank. But unfortunately, baby scales are not small, and most people do not own baby scales. So, while that can provide an estimate, it's not convenient."
As another option, mothers can pump breastmilk into a bottle. While bottle-feeding offers precise volume measurements and visual reassurance that the baby is consuming milk, it removes the benefits of skin-to-skin contact. And the extra steps of pumping, storing and handling milk are time-consuming and can even increase the risk of bacterial contamination.
"There are several advantages to breastfeeding at the breast compared to feeding breast milk with a bottle," Wicks said. "First and foremost, that skin-to-skin bond is beneficial for both babies and moms. Additionally, milk production is oftentimes stimulated better by actual breastfeeding."
Although other academic researchers and small startup companies have explored technologies to monitor aspects of breast milk and feeding, peer-reviewed studies are scarce.
"Based on our reviews of the scientific literature and our discussions with pediatricians and neonatologists, there are no clinically validated technologies that address this important medical need," Rogers said. "Our work fills that gap."
Pinpointing the right strategy
Rogers' team previously developed soft, flexible wireless body sensors for monitoring babies in the NICU as well as wearable sensors for tracking the drainage of fluid flow through shunts, which are commonly used to treat patients with hydrocephalus. With experience working with vulnerable populations and developing devices capable of measuring fluid flow, Rogers and his team were ideal candidates for the project.
"Our clinical colleagues asked us whether we could develop a sensor that would allow new mothers to determine how much milk their babies are consuming during a nursing session," Rogers said. "At first, we weren't sure how to approach the problem. The strategies we used to track flow through shunts as they pass through locations superficially below the skin don't work because milk ducts lie too far beneath the skin's surface."
After years of failed attempts based on methods to monitor the optical properties of the breast, to quantify suckling motions, to track swallowing events and several others, the engineers finally settled on a remarkably simple technique. The device sends a tiny, safe electrical current through the breast using two small pads, or electrodes, placed on the skin. Another pair of electrodes captures the voltage difference associated with that current.
As the baby drinks milk, the amount of milk in the breast decreases. This reduction leads to a change in the electrical properties of the breast in a subtle but measurable manner. These changes directly relate to the amount of milk removed from the breast. The larger the amount, the bigger the change in electrical properties. Though subtle, that change can be accurately calibrated and quantified for real-time display on a smartphone during breastfeeding.
"This is a concept called bioimpedance, and it's commonly used to measure body fat," Rogers said. "Because muscle, fat, bone and tissues conduct electricity differently, bioimpedance can yield an accurate measurement of fat content. In a conceptually similar way, we can quantify the change in milk volume within the breast. This was the last strategy we tried, unfortunately. But fortunately, we found that we were able to make it work really well."
Rigorous testing
After designing initial prototypes, the engineering team optimized it through several stages of testing and modeling. First, they built simplified models of a breast using materials that mimic the electrical properties of skin, fat and milk. By precisely controlling the amount of "milk" in these models, the researchers could see how the device's data changed as the volume of "milk" changed.
Led by Avila at Rice, the team then created detailed computer models of the breast, based on real anatomy. Their physics-based computer simulations monitored the physiological changes that occur during breastfeeding. Using bioimpedance, Avila linked the flow of electrical signals to the amount of milk leaving the breast in real time. His team's anatomically correct computer models incorporate patient-specific breast shapes and tissue distributions, enabling them to test how sensor placement and tissue variation affect readings.
"Our simulation results matched the trends of experiments and human clinical studies," Avila said. "Connecting our models to impact in the real world is always a highlight, and it's only possible through the collaboration among experimental, modeling and clinical teams."
Personalized for all shapes and sizes
The resulting device is a thin, soft, pliable cord that lightly wraps around the outer circumference of the breast. Electrodes, which gently adhere to the skin, are integrated into each end of the cord. A small, lightweight "base station," which also softly mounts onto the skin, sits in the middle of the cord between the electrodes. Enclosed in a soft, silicone case, the base station holds a small rechargeable battery, Bluetooth technology for wireless data transfer and a memory chip.
Because every mother has differences in breast density, shape and size, the device can be personalized through a single calibration. To calibrate the system, the mother wears the device while using a breast pump connected to a bottle with volume markings. This enables the user to know the precise volume of milk being expressed over a specific period of time. Meanwhile, the device records the breast's electrical properties throughout the pumping process. This calibration scheme teaches the device how to interpret the changes in electrical signals for each specific mother.
After developing prototypes, the team tested the device on 12 breastfeeding mothers — both in the NICU and at home. To assess whether the device was consistent and reliable over time, the researchers took multiple measurements from the same mothers, spans of time as long as 17 weeks.
In this first stage of testing, mothers wore the sensor while they pumped as this important step required knowing precisely the amount of milk mothers expressed. In one testing session, the researchers compared the device's data to the difference in the baby's weight before and after breastfeeding. Overall, with the testing during pumping, the results between amounts in the bottle and amounts detected by the sensor were strikingly similar.
Improving care in the NICU
While the device would provide reassurance and useful information to all parents, Robinson and Wicks say NICU babies would benefit the most from careful monitoring. Knowing exactly how much a baby in the NICU is eating is even more critical than for healthy, full-term infants.
These babies often have precise nutritional needs. Premature babies, for example, may have underdeveloped digestive systems, making them more vulnerable to feeding intolerance. Precise feeding volumes can help minimize the risks of developing intestinal disorders and reflux.
"Some babies are limited to a certain number of feeds at a time," Wicks said. "For babies who are born prematurely or who are recovering from a surgery, they can only eat small amounts of milk very slowly. Oftentimes, we cannot allow them to breastfeed because there's no way for us to know how much milk they are getting from mom. Having a sensor to monitor this would enable these babies to breastfeed more successfully with their mom."
Future directions
To become even more user-friendly, the researchers envision the technology eventually could be integrated into comfortable undergarments like breastfeeding bras. This would further enhance the device's ease of use and overall experience for mothers.
The researchers still plan to complete comprehensive comparisons to the pre- and post-feed weighing. The team also aims to ensure the sensor is usable for mothers with a wide range of skin tones. While the current version of the device detects the amount of milk flowing out of the breast, future iterations could measure milk refilling into the breast. Then mothers could track changes in milk production over time. The team also plans to continue optimizing the device so it can glean even more insights, such as milk quality and fat content.
"Breastfeeding can be extremely emotional for mothers, in part due to the uncertainty surrounding how much milk their babies are getting," Wicks said. "It can come with a lot of sadness because mothers feel anxious and like they aren't doing a good job. Oftentimes, mothers experience anxiety, frustration or symptoms of depression and give up on breastfeeding altogether.
"There are many factors that make breastfeeding difficult. Being able to remove one piece of uncertainty and being able to help reassure them that they are producing enough milk will really help decrease some of that stress and anxiety. For all moms around the world — who are in all different stages of their breastfeeding journeys — this device will be incredibly helpful. We're looking forward to bringing it to more people."
The study, "A compact, wireless system for continuous monitoring of breast milk expressed during breastfeeding," was supported by the Querrey Simpson Institute for Bioelectronics, the Defense Health Agency, the National Research Foundation of Korea and the Haythornthwaite Foundation.
