Fetal Monitors WHO. “Fetal Monitor.” From the publication: Core Medical Equipment. Geneva, Switzerland, 2011

Quiz Clinical Use History Specifications Principles of Operation Block Diagram Commercial Examples Preventive Maintenance Common Problems Test Procedures Summary

1.How can one measure the mother contractions? With each sensor? 2.What are the technologies for fetal monitoring? Describe one advantage and one problem from each. 3.Draw a block diagram from a Doppler monitor? 4.How can one test a monitor without a pregnant woman? Quiz

Fetal Heart Rate 110 to 160 beats a minute Strong and regular beat sounds During labor the fetal heart rate can change with distress

Clinical Use Fetus heart rate Mother contractions (Tocodynamometer) –Strain gage (TOCO) transducer with a belt around the abdomen Developing World Healthcare Technology Laboratory. “Fetal Monitors.” From the Publication: “Biomedical Technicians Training Program, Session 3 v2, Special Topics: Cardiac Equipment.” Engineering World Health, March 1, 2011, p

History Stethoscope allowed to hear the fetal heart beat 1960’s - Prof. K. Hammacher (Hewlett-Packard) began Electronic fetal monitor (microphone)

Input –Electrical –Mechanical (ultrasound) Output –Electronically (display) –Mechanical: sound –Paper Specifications

Types of Fetal Monitor Surface Electrodes Scalp Electrode Doppler (most common): WHO. “Fetal Heart Detector, Ultrasonic.” From the publication: Core Medical Equipment. Geneva, Switzerland, 2011

Surface Electrodes Principles of Operation Operates like an electrocardiogram Adhesive Ag/AgCl electrodes in contact with the mother’s body

Surface Electrodes Principles of Operation Developing World Healthcare Technology Laboratory. “Fetal Monitors.” From the Publication: “Biomedical Technicians Training Program, Session 3 v2, Special Topics: Cardiac Equipment.” Engineering World Health, March 1, 2011, p

Advantages: –Not invasive –Works on any time during pregnancy –Very low cost Limitations: –Artifacts from the maternal heart beat –Don’t work well with certain fetal positions –Can’t resolve multiple fetal pregnancies Surface Electrodes Principles of Operation

Advantages: –Accurate signal Limitations: –Invasive –Cannot be applied to multiple fetal pregnancies Scalp Electrodes Principles of Operation

Doppler Principles of Operation Dirk Hünniger (Own work) [GFDL ( or CC-BY-SA-3.0 ( via Wikimedia Commons

Doppler Principles of Operation WHO. “Foetal Cardiac Monitor.” From the publication: “WHO Technical Specifications for 61 Medical Devices. WHO. Retrieved from:

Advantages: –Not invasive –Less artifacts Limitations: –Expensive –Don’t work well with certain fetal positions –Can’t resolve multiple fetal pregnancies Doppler Principles of Operation

Fetal Heart Activity Signals Jezewski, L. et.al. “A Novel Technique for Fetal heart Rate Estimation for Doppler Ultrasound Signal.” BioMedical Engineering OnLine, Vol. 10, No. 92 (2011). Retrieved from:

Commercial Examples IAEYQ_AUIBygB&dpr=2

Commercial Examples Harmid (2010), Fetal Monitor [picture]. Retrieved from

Contractions belts: Stretch belt strength on the mothers belly Scalp electrodes: opens the amniotic sac for infection Patient’s Safety

Check batteries Preventive Maintenance

Broken leads Dirty probes (gel) Dead batteries Wrong paper feeding Common Problems

Use watch to verify correct hear rate Electrodes: Test on yourself (mother) and another to a friend (fetus) Test Procedures

Doppler : Check for noises when tapping the probe with your hands Test heart rate on yourself Test Procedures WHO. “Fetal Monitor.” From the publication: Core Medical Equipment. Geneva, Switzerland, 2011.

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