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Womens Health

Women's Health - Poster Session C

Poster L22 - Fetal Blood Sampling Device: Fetal Distress Detection Using pH Monitoring

Friday, October 25, 2024
10:00 AM - 11:00 AM EST
Location: Exhibit Hall E, F & G

Introduction:  The global rise of Cesarean deliveries (C-sections) without significant decrease in maternal or neonatal morbidities suggest inaccuracies in current diagnostic procedures. This issue is urgent considering the higher cost and morbidity rate of C-sections against vaginal deliveries. The determining factor to perform a C-section is fetal distress, which indicates insufficient oxygen for the fetus during labor. Signs include low amniotic fluid, changes in fetal heart rate, and reduced fetal movement. The US current standard of care to diagnose fetal distress is cardiotocography (CTG), which measures fetal heart rate, fetal movement, and contractions. However, CTG has high sensitivity and low specificity from factors like fetal movement and maternal medication that influence fetal heart rate without suggesting distress. Additionally, a lack of standardization results in subjective interpretation of CTG scans. Both contribute towards unnecessary diagnosis for C-sections. A recent review of C-sections found using CTG on low-risk pregnancies increased C-sections by 20% with no effect on perinatal outcomes. A more viable diagnosis method is fetal blood sampling (FBS), which measures fetal scalp blood pH for signs of hypoxia. Measuring pH instead of relying on CTG scans provides a more objective indication of fetal distress since anaerobic respiration produces lactic acid, which lowers the blood pH below the healthy range (>7.25). While performed globally, FBS is not widely adopted in the US because of the lengthy procedure and multiple tools required to perform it. Our laboratory has created a handheld FBS solution that is more efficient and user-friendly than the current FBS kit.

Materials and

Methods:  Our project aims to develop a FBS device that consolidates the kit into a single device that utilizes pH measurements to detect fetal distress through iterative design and development with US OB/GYN advisors. This device consists of a pH meter, retractable lancet, Q-tip, and capillary tube to collect fetal blood and measure the pH levels. Buttons are used to control the deployment of components, and the housing is modeled after a speculum to mimic the comfortability of a ubiquitous device utilized by OB/GYNs (Figure 1). The designed modularization of the device allows for easy replacement of contaminated components for sterilization to reduce potential infection and waste.
Verification testing was performed with clinician input to ensure the device met the design criteria above. The device was tested for incision depth, where the lancet should penetrate the surface by 2mm. Volume accuracy was tested, where the capillary tube should collect 0.3mL of fluid. The sensitivity and specificity of the pH meter was tested to determine whether it can detect distress from proxies for fetal blood. The pH tests measured the range of the pH meter given low to high levels of blood oxygen given the Quality Care Guidelines for intrapartum surveillance. Values for a normal pH range should be 7.25 or greater, and ranges lower than this are considered abnormal, indicating retesting or the need for a C-section. Preliminary safety tests were conducted using orange juice, alkaline water, and control solutions of pH 7.01 and 4.01 to ensure desired sensitivity and specificity.

Results, Conclusions, and Discussions: Given iterative feedback from our US OB/GYN advisors, the device was required to be operable with one hand and ergonomic. However, the retraction of components were rough and difficult. The positioning of the handle created slight discomfort when holding the device. To verify the ability of the device to adequately perform the FBS procedure, 10 trials were conducted to measure the incision depth and sample volume accuracy. The deployment of the lancet was consistent with an incision depth of 2mm±0.33mm. Similarly, the capillary tube showed consistency in volume accuracy as it drew fetal blood volume of 0.3mL±0.02mL.
The evaluation of the pH sensitivity and specificity showed consistent measurements of the control solutions and the testing solutions. The pH meter was calibrated with control solutions, therefore the spread of data collected for the 4.01 and 7.01 pH solutions was marginal, showing accuracy of pH measurements. Further testing utilized orange juice and alkaline water to test solutions close to the calibration buffers, with alkaline water serving as a solution close to the pH of human blood and orange juice used as a proxy for abnormal pH levels. The pHs of orange juice and alkaline water are 3.92 and 7.4 respectively, and successive trials reached these values (Figures 2 and 3). These results showed how pH readings can become indicators of fetal distress, as changes were detected efficiently using the FBS device. However, the current meter proved to be too insensitive to measure the outputs necessary to determine fetal distress, as these values were not detected when using solutions of 7.01 to 7.25. Further testing will be required to assess the sensitivity of the pH meter.
For future work, the housing will be revised to offer ease of use and improve its ergonomics. In particular, this redesign should put less strain on the wrist. With all of the parts assembled inside the housing, faster testing can be accomplished than with standard FBS kits that require assembly. Use of lactate meters to determine fetal distress will be explored, as this has been found to be a better indicator of fetal distress in recent research.

Acknowledgements (Optional):  We would like to acknowledge Dr. Christine King and Dr. Dinh Vu for their valuable guidance and feedback towards the development of this project. This project was supported by the Undergraduate Research Opportunities Program at the University of California Irvine.