A handheld milk conductivity sensing device (Mylee) for measuring secretory activation progress in lactating women: a device validation study

Abstract

Background: Human milk electrolytes are known biomarkers of stages of lactation in the first weeks after birth. However, methods for measuring milk electrolytes are available only in laboratory or expert settings. A small handheld milk sensing device (Mylee) capable of determining on-site individual secretory activation progress from sensing the conductivity of a tiny milk specimen was developed. Here we evaluate the validity of a novel milk-sensing device (Mylee) for measuring the progress of milk maturation and secretory activation status.

Methods: Retrospective data analysis of laboratory records generated using the Mylee device. Device conductivity measurements were assessed for accuracy, reliability and stability in rigorous laboratory tests with standard materials. A set of human milk specimens (n = 167) was used to analyze the agreement between the milk maturation score and laboratory measurements of the secretory activation biomarker milk sodium [Na+].

Results: The Mylee device was demonstrated to have excellent reproducibility (CV_95%<5%) and accuracy (error < 5%) for conductivity measurements of a small specimen (350 µl), with good device stability and almost perfect inter-device unit reliability (ICC > 0.90). With regression analysis, we revealed excellent agreement between Mylee milk maturation (MM%) output or its raw conductivity signal and laboratory measurements of conductivity and sodium [Na+] in a dataset of milk specimens (n = 167; R² > 0.9). The Mylee MM% score showed good predictive ability for secretary activation status, as determined by sodium threshold (18 mmol/L) in human milk specimens.

Conclusions: In this study, we demonstrated the reliability and validity of the Mylee device and its ability to detect on-site milk secretory activation in a manner comparable to that of electrolyte-based methods. The novel MyLee device offers the potential to generate real-time information about the lactation stage, measured by mothers at the commodity of their home.

Keywords: Biomarkers; Breastfeeding, feasibility studies; Human milk; Lactogenesis; Milk supply; Mobile health; Remote sensing technology; Retrospective studies; Secretory activation.

Fig. 1

Schematic representation of the Mylee device and app. A milk well is designed to hold a predefined small milk specimen volume when the Mylee device is placed on top. The device is connected via Bluetooth to a smartphone and operated via the Mylee app. The milk data are transferred from the device to the app, and the Milk maturation percentage is computed based on server-based algorithm logic

Fig. 2

Device measurements are reliable for a range of specimen temperature and volume. (A) Milk well 3D illustration and middle slice cross view illustrating the central cavity volume (300–350 µl). (B) The conductivity of specimens gradually elevated from 200 µl to 450 µl as recorded by the Mylee device in two levels of standard conductivity solution. red X - The system alerted of insufficient specimen volume for measuring. (Ci) Series of conductivity measurements by device vs. specimen temperature in a bath-warmed standard sample left to cool to ambient temperature (Starting Temp 39 °C, End Temp 30 °C; yellow) and a Fridge-cooled standard sample left to warm to ambient temperature (Starting Temp 17 °C, End Temp 24.7 °C; blue). Two Room Temp standard samples were included for comparison (26.4 °C; 27.6 °C, black). (Cii) Conductivity measurements of two levels of standard materials from 10 different measurement dates performed at various ambient temperatures. The X-axis represents the sample temperature as measured by the device

Fig. 3

Device measurements are stable and reliable over time. (A) Linear regression of conductivity to KCl molarity in the measuring range of 10–100 mM. (B) Levey–Jennings chart of the quality control data logged by one of the devices tested for stability, with two levels of conductivity standard solution (Level 1 (1413 µS/cm) and Level 2 (5.00 mS/cm)) collected over a 2-month period. The middle line is the mean, and the dashed line measures the distance from the mean to the standard deviation. (C). Test-retest analysis to assess the consistency of the measurement set-over devices by comparing conductivity records in a set of 28 mothers’ milk specimens

Fig. 4

The measurements from the Mylee device were comparable to milk sodium measurements in human milk (n = 167). Correlation plots of the device (A) milk maturation (MM%) and (B) raw conductivity against the specimen Na + concentration recorded by the ISE (LAQUATwin, HORIBA)

Fig. 5

MM% reflects classification based on sodium limits in milk specimens. Records of mother’s milk specimens divided into two classes according to baby age records (A) 5–10 days, (B) 11–60 days after birth) and categorized into two subgroups based on milk Na + levels. Group differences were tested by two factor ANCOVA, followed by the Tukey test (*** P < .001)

Fig. 6

Mylee App interface example depicting MyLee device measurement records for each breast at 12 days after delivery. Most recent measurements are assigned a color index according to the App proprietary algorithm relative to population benchmarks of good predominant breastfeeding benchmarks. All measurement records are presented as a chart (blue - left side, Gray - right side), where lines represent progression between days. Population benchmarks are marked as background in green and light green (15th, 50th, and 80th percentile limits)