Maternal contribution detection during fetal heart monitoring

1. A method comprising:

acquiring an ultrasound signal from a fetal heart from an ultrasound transducer;

determining a fetal heart signal contribution to the ultra sound signal by suppressing any maternal contribution from the ultrasound echo signal, wherein the fetal heart signal contribution is a component of an ultrasound Doppler echo signal that is caused by pulsations of a fetal heart and wherein a maternal contribution is a component of an ultrasound Doppler echo signal that is caused by pulsations of blood in maternal abdominal muscles;

canceling the fetal heart signal contribution from the ultrasound signal; and

triggering an alarm based upon a result of the cancellation.

2. The method of claim 1 , further comprising:

determining an existence of a first heart rate detected on any remaining signal following the cancellation; and

evaluating a coincidence of the first heart rate with a second heart rate detected on the ultrasound signal, wherein the alarm is outputted if the first heart rate exists and does not satisfy a predetermined degree of coincidence with the second heart rate.

3. The method of claim 1 , wherein the ultrasound signal is acquired by:

determining an approximate distance between an ultrasonic transducer and the fetal heart; and

sensing a range of distances from the ultrasonic transducer using the ultrasonic transducer, the range having a minimum distance based upon the approximate distance.

4. The method of claim 3 , wherein the range has a maximum distance based on the approximate distance.

5. The method of claim 4 , wherein the minimum distance of the range is spaced from the approximate distance by a spacing.

6. The method of claim 4 , wherein the minimum distance of the range and the maximum distance of the range form a window enclosing and spaced from the fetal heart.

7. The method of claim 4 , wherein determining the approximate distance comprises sensing overlapping depth zones, wherein the approximate distance is determined based upon overlapping portions of two adjacent depth zones at which strength of an echo signal is highest.

8. The method of claim 7 further comprising selecting the two adjacent depth zones from a plurality of pairs of adjacent depth zones based upon coincidence of heart rates of ultrasound signals reflected from each pair of the plurality of pairs of adjacent depth zones with a fetal heart rate of ultrasound signals reflected from an entire range of all the plurality of pairs of adjacent depth zones.

9. The method of claim 1 , wherein the determining of a fetal heart signal contribution to the ultra sound signal and the canceling of the fetal heart contribution from the ultrasound signal comprises:

autocorrelating the ultrasound signal;

obtaining periods between first fetal heartbeats;

identifying a minimum of the periods;

cutting off segments of the ultrasound signal, wherein each segment has a length corresponding to the minimum and is aligned with the first fetal heartbeat;

normalizing each segment by an amplitude of the first fetal heartbeat in the segments;

determining an average of the normalized segments; and

subtracting a denormalized averaged segment from each segment .

10. A fetal heart monitoring system comprising:

an ultrasonic transducer;

an alarm;

a controller configured to generate control signals directing the operation of the ultrasonic transducer and to receive echo signals from the ultrasonic transducer, the controller configured to:

acquire an ultrasound signal from a fetal heart from the ultrasound transducer; and

determine a fetal heart signal contribution to the ultrasound signal by suppressing any maternal contribution from the ultrasound signal, wherein the fetal heart signal contribution is a component of an ultrasound Doppler echo signal that is caused by pulsations of a fetal heart and wherein a maternal contribution is a component of an ultrasound Doppler echo signal that is caused by pulsations of blood in maternal abdominal muscles;

cancel the fetal heart signal contribution from the ultrasound signal; and

triggering the alarm based upon a result of the cancellation.

11. The fetal heart monitoring system of claim 10 , wherein the controller is configured to:

determine an existence of a remaining signal following the cancellation; and

evaluate a coincidence of a heart rate detected on any remaining signal with a heart rate detected on the ultrasound signal, wherein the alarm is outputted if the remaining signal exists and does not coincide with the heart rate detected on the ultrasound signal.

12. The fetal heart monitoring system of claim 10 , wherein the ultrasound signal is acquired by:

determining an approximate distance between an ultrasonic transducer and the fetal heart; and

sensing a range of distances from the ultrasonic transducer using the ultrasonic transducer, the range having a minimum distance based upon the approximate distance.

13. The fetal heart monitoring system of claim 10 , wherein the controller is configured to suppress the maternal contribution from the ultrasound signal by:

autocorrelating the ultrasound signal;

obtaining periods between first fetal heartbeats;

identifying a minimum of the periods;

cutting off segments of the ultrasound signal, wherein each segment has a length corresponding to the minimum and is aligned with the first fetal heartbeat;

normalizing each segment by an amplitude of the first fetal heartbeat in the segments;

determining an average of the normalized segments; and

subtracting a denormalized averaged segment from each segment.

14. An apparatus comprising:

a non-transitory computer-readable medium containing computer-readable code to direct a processor to:

acquire an ultrasound signal from a fetal heart from an ultrasound transducer;

determine a fetal heart signal contribution to the ultrasound signal by suppressing any maternal contribution from the ultrasound signal, wherein the fetal heart signal contribution is a component of an ultrasound Doppler echo signal that is caused by pulsations of a fetal heart and wherein a maternal contribution is a component of an ultrasound Doppler echo signal that is caused by pulsations of blood in maternal abdominal muscles; and

cancel the fetal heart signal contribution from the ultrasound signal; and

output an alarm based upon a result of the cancellation.

15. The apparatus of claim 14 , wherein the non-transitory computer-readable medium contains computer-readable code to direct the processor to:

determine an existence of a first heart rate detected on any remaining signal following the cancellation; and

evaluating a coincidence of the first heart rate with a second heart rate detected on the ultrasound signal, wherein the alarm is outputted if the first heart rate exists and does not satisfy a predetermined degree of coincidence with the second heart rate.

16. The apparatus of claim 14 , wherein the non-transitory computer-readable medium contains computer-readable code to direct a processor to:

determine an approximate distance between an ultrasonic transducer and the fetal heart;

sense a range of distances from the ultrasonic transducer using the ultrasonic transducer, the range having a minimum distance based upon the approximate distance; and

monitor a heart rate of the fetal heart using ultrasonic echo signals from the range.

17. The apparatus of claim 16 , wherein the computer-readable code is configured to direct the processor to determine the approximate distance by sensing overlapping depth zones, wherein the approximate distance is determined based upon overlapping portions of two adjacent depth zones at which strength of an echo signal is highest.

18. The apparatus of claim 17 , wherein the computer-readable code is further configured to direct the processor to select the two adjacent depth zones from a plurality of pairs of adjacent depth zones based upon coincidence of heart rates of ultrasound signals reflected from each pair of the plurality of pairs of adjacent depth zones with a fetal heart rate of ultrasound signals reflected from an entire range of all the plurality of pairs of adjacent depth zones.

19. The apparatus of claim 14 , wherein the computer-readable code is configured to direct the processor to cancel the fetal heart signal contribution from the ultrasound signal by:

autocorrelating the ultrasound signal;

obtaining periods between first fetal heartbeats;

identifying a minimum of the periods;

cutting off segments of the ultrasound signal, wherein each segment has a length corresponding to the minimum and is aligned with the first fetal heartbeat;

normalizing each segment by an amplitude of the first fetal heartbeat in the segments;

determining an average of the normalized segments; and

subtracting a denormalized averaged segment from each segment.

20. The apparatus of claim 14 , wherein the computer-readable code is further configured to direct the processor to identify a window about the fetal heart and to acquire the ultrasound signal solely from within the window.