CN107822633B - Fetal weight estimation method - Google Patents

Fetal weight estimation method Download PDF

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CN107822633B
CN107822633B CN201710880315.3A CN201710880315A CN107822633B CN 107822633 B CN107822633 B CN 107822633B CN 201710880315 A CN201710880315 A CN 201710880315A CN 107822633 B CN107822633 B CN 107822633B
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electrode
impedance
pregnant woman
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excitation
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CN107822633A (en
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王萍
陈波
俞洁
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Beijing Kangping Technology Co ltd
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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/05—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves 
    • A61B5/053—Measuring electrical impedance or conductance of a portion of the body
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/05—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves 
    • A61B5/053—Measuring electrical impedance or conductance of a portion of the body
    • A61B5/0537—Measuring body composition by impedance, e.g. tissue hydration or fat content
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/43—Detecting, measuring or recording for evaluating the reproductive systems
    • A61B5/4306—Detecting, measuring or recording for evaluating the reproductive systems for evaluating the female reproductive systems, e.g. gynaecological evaluations
    • A61B5/4343—Pregnancy and labour monitoring, e.g. for labour onset detection
    • A61B5/4362—Assessing foetal parameters

Abstract

The invention provides a pregnant woman abdomen segmented impedance measuring method and a fetus weight estimating method, wherein the pregnant woman abdomen segmented impedance measuring method comprises the following steps: establishing a four-port network for pregnant woman abdominal section impedance measurement; and calculating the abdominal segmented impedance of the pregnant woman according to the four-port network. According to the pregnant woman abdomen segmented impedance measuring method, the pregnant woman abdomen segmented impedance is obtained through measurement, the fetal weight is estimated based on the obtained pregnant woman abdomen segmented impedance, B-ultrasonic detection and uterine height measurement are not needed, and the cost and complexity of fetal weight estimation are effectively reduced.

Description

Fetal weight estimation method
Technical Field
The invention relates to the technical field of family planning, in particular to a fetal weight estimation method.
Background
The change of the weight of the fetus has important research significance for the health monitoring of pregnant women in the gestation period, the size of the weight of the fetus directly determines the selection mode of the pregnant women to be delivered, and the safety of the pregnant women and the fetus can be effectively ensured. Fetal weight is one of the important factors determining the manner of delivery.
In recent decade, the cesarean section yield of China is high due to multiple aspects, the fact that the fetal weight cannot be accurately predicted is one of important reasons, and a doctor cannot well guide a pregnant woman to select a delivery mode because the fetal weight cannot be accurately estimated. On the other hand, the wrong estimation of the fetal weight may cause various dystocia in the trial delivery process, such as shoulder dystocia, brachial plexus injury, and neonatal asphyxia. Therefore, accurately predicting the fetal weight is an important basis for a doctor to clinically treat the pregnant woman, and is a powerful guarantee for reducing the complications of the dangerous infants and reducing the cesarean section yield.
At present, the formula for predicting the fetal weight through the double apical diameters of the fetus is more, most of the formulas are more complex, and the memory and the popularization are difficult. Although the fetal abdominal circumference is a good index for predicting the fetal weight, the measurement of the fetal abdominal circumference is affected by the amniotic fluid volume and the fetal orientation, and the measurement error is still large. The ultrasonic wave has no damage, simple and convenient use and accurate measurement, so the method can be used for predicting the size of the fetus. By using the ultrasonic to measure various biological indexes of the fetus, the growth and development conditions of the fetus can be judged, and the method has important significance for accurately estimating the weight of the fetus. The formula for predicting the fetal weight by ultrasonic is many, and the factors such as fetal liver, fetal abdominal subcutaneous tissue, femoral length, head circumference, abdominal circumference and the like measured by ultrasonic are reported in documents, and the correlation with the fetal weight is high. In actual operation, ultrasonic measurement has high requirements on the technical level of inspectors, the display of the abdominal circumference layer can be influenced by various complex conditions, and the accurate abdominal circumference measurement value is difficult to obtain if the standard layer cannot be displayed.
In non-patent document 1, a mathematical formula for estimating the weight of a fetus is established by songxiaofeng and the like according to parameters such as the height of the uterus, the circumference of the abdomen and the like of a pregnant woman and indexes such as the double apical diameter, the length of the femur, the circumference of the abdomen and the like of a B-ultrasonic measurement fetus, but the method has a large error of a prediction result according to empirical regression analysis.
In non-patent document 2, the influence of factors such as abdominal wall fat thickness and presenting height is considered by the liu cheng jun, and the like, and fetal weight estimation is mainly based on uterine height and abdominal circumference, but measuring the abdominal wall thickness before delivery has great difficulty in clinical application.
In non-patent document 3, yaosmin et al predict fetal weight by measuring liver area using B-ultrasound, and the increase in fetal weight in the late gestation is mainly associated with accumulation of fat and storage of liver glycogen. However, when the fetus is over-nourished, the liver area is increased, which causes a larger error; meanwhile, the abdominal circumference ultrasonic measurement accuracy of primary hospitals is poor, and the clinical application is influenced.
In non-patent document 4, researchers such as wujun use artificial intelligence methods such as artificial neural networks to measure the fetal weight, so that the prediction accuracy is improved to a certain extent, but the artificial neural networks have the defects of complex network structures, long training time and the like, and clinical verification needs to be promoted.
Non-patent document 5 discusses the relationship between maternal components during pregnancy and the birth weight of a newborn, and statistical analysis shows that the increase in pregnancy weight is related to changes in various maternal components, but does not provide a model for estimating the body components and the fetal weight.
Documents of the prior art
Non-patent document 1: new method [ J ] for predicting body weight of foot-month fetus based on support vector machine (Zhao Xiao, Hanping, Zhooli, Chengzhao, Chilobrachys) and Chilobrachys, China biomedical engineering, 2004, (06):516 plus 522.
Non-patent document 2: liu Zhijun, Li Gui Rong, Guo Xingqiao, comparison of the new method for predicting the fetal weight with the traditional method [ J ], Chinese maternal and child health care, 2008, (24): 3478-.
Non-patent document 3: yaoqin, Panvemin, Shaohongshui, Liupei autumn, the value of predicting the fetal weight by B-ultrasonic measurement of fetal liver area [ J ], Shandong medicine, 2003, (24): 15-16.
Non-patent document 4: wujun, Taizhu, Linjiang Li, Luhong, Lideyu, Wangtianfu, Zhengchangqiong, and the method for predicting body weight of full-term fetus based on artificial neural network [ J ], journal of biomedical engineering, 2005, (05):922 + 925+ 929.
Non-patent document 5: chen gan, xu Ping, Li Jie, Wang Zhi crowd, Zhao Xia, Shenshan Mei, Wang Jing, Wang Shuan, relationship between maternal component of pregnancy and birth weight of newborn, Chinese woman and child health care, 2015, 30(1): 54-57.
According to the analysis of the documents, the domestic pregnant woman fetal weight measurement is mostly based on B-ultrasonic and uterine height methods, and the following defects exist:
(1) most measurement methods are based on a linear regression model, the measurement cost is high, the measurement mode is complex, the estimation error is large, and the measurement precision is greatly influenced by the sample size;
(2) the pregnant woman in the gestation period needs to carry out multiple measurements according to the gestation week, the safety of the pregnant woman and a fetus needs to be ensured in the measurement process, and the burden of operators and the measurement times of the pregnant woman are increased.
Disclosure of Invention
In view of the above, the present invention provides a pregnant woman abdomen segmented impedance measuring method and a fetus weight estimating method, which can effectively reduce the cost and complexity of estimating the weight of the fetus without performing B-ultrasonic detection and uterine height measurement.
In order to solve the technical problems, the invention adopts the following technical scheme:
on one hand, the pregnant woman abdominal segmented impedance measuring method according to the embodiment of the invention comprises the following steps:
establishing a four-port network for pregnant woman abdominal section impedance measurement;
and calculating the abdominal segmented impedance of the pregnant woman according to the four-port network.
According to the four-port network disclosed by the embodiment of the invention, the segmented measurement of the abdominal impedance of the pregnant woman can be realized, and the technical support is provided for analyzing the abdominal impedance and the body composition change and estimating the weight of the fetus during pregnancy.
According to some embodiments of the invention, the four-port network comprises two measurement electrodes and two excitation electrodes.
Optionally, the two measuring electrodes are respectively a first measuring electrode and a second measuring electrode, the first measuring electrode connects the left waist and the right waist of the pregnant woman, and the second measuring electrode connects the waist of one side of the pregnant woman and the hip of the one side;
the two excitation electrodes are respectively a first excitation electrode and a second excitation electrode, the first excitation electrode is connected with the left side hip and the right side hip of the pregnant woman, and the second excitation electrode is connected with the waist of the other side of the pregnant woman and the hip of the other side of the pregnant woman.
Further, the four-port network may be excited by the first excitation electrode and the second excitation electrode, respectively, to calculate four-segment impedances corresponding to the first measurement electrode, the second measurement electrode, the first excitation electrode, and the second excitation electrode.
Specifically, a predetermined current may be applied to both ends of the first excitation electrode to excite the first excitation electrode, and a voltage difference between the first excitation electrode and the first measurement electrode, between the second excitation electrode and the second measurement electrode, between the first excitation electrode and the second excitation electrode may be measured,
inputting the predetermined current to two ends of the second excitation electrode for excitation, and measuring the voltage difference between the second excitation electrode and the first measuring electrode, the second measuring electrode and the first excitation electrode,
and calculating four sections of impedances corresponding to the first measuring electrode, the second measuring electrode, the first exciting electrode and the second exciting electrode according to the voltage differences between the first exciting electrode and the first measuring electrode, the second measuring electrode and the second exciting electrode and the voltage differences between the second exciting electrode and the first measuring electrode, the second measuring electrode and the first exciting electrode.
On the other hand, the fetal weight estimation method according to the embodiment of the present invention includes the steps of:
measuring the abdominal segmental impedance of the pregnant woman by using the pregnant woman abdominal segmental impedance measuring method according to any one of the embodiments;
obtaining the equivalent impedance of the abdomen according to the segmented impedance of the abdomen;
establishing a fetal weight estimation model according to the abdominal equivalent impedance;
calculating the fetal weight according to the fetal weight estimation model and the physical parameters of the pregnant woman.
The calculation formula of the equivalent impedance is shown as the following formula:
Figure GDA0003171419020000061
wherein R isEquivalence ofRepresents the equivalent impedance, R1、R2、R3、R4Respectively representing four sections of impedance corresponding to the four-port network.
According to some embodiments of the present invention, abdominal segment impedance and abdominal equivalent impedance at 2 different frequency bands (e.g. 250Hz and 500Hz) are calculated respectively, and the fetal weight estimation model is established according to the abdominal segment impedance and abdominal equivalent impedance at the different frequency bands and the physical parameters of the pregnant woman.
Further, the fetal weight estimation model is represented by the following formula:
Y＝78*(Ti-20)+(α*H*H)/R250 equivalent+(β*ΔW)/R500 equivalent
Wherein Y is fetal body weight in grams (g); h is the abdominal circumference of the pregnant woman in centimeters (cm); Δ W is the weight gain of the pregnant woman, the weight difference with the weight of the progestational precursor during detection, and the unit is gram (g); t isiIs the gestational week; r250 equivalent、R500 equivalentRespectively, represent the 1 st frequency band (i.e., 250H)z) and the equivalent impedance under the 2 nd frequency band (namely 500Hz), and alpha and beta are reference coefficients.
Still further, the reference coefficient α is calculated by the following formula:
Figure GDA0003171419020000062
the reference coefficient β is calculated by the following formula:
Figure GDA0003171419020000063
wherein R is250、R500、Y、H、ΔW、TiAll the test data are the test data in the 1 st sample; r250'、R500'、Y'、H'、ΔW、TiFor the test data in item 2, R is added250 equivalentIs recorded as R250R is to be500 equivalentIs recorded as R500R is to be250 equivalent' Note R250', introduction of R500 equivalentIs recorded as R500′。
Optionally, a group of test samples are selected, the fetal weight is estimated according to the obtained alpha and beta values according to the actual physical parameters of the pregnant women of the test samples, the estimated weight is compared with the actual weight of the test samples, two samples with the smallest error are selected to recalculate the reference coefficients alpha and beta, and the fetal weight estimation model is established according to the recalculated alpha and beta.
Preferably, the Ti is greater than or equal to 25.
The technical scheme of the invention at least has one of the following beneficial effects:
(1) the pregnant woman abdomen segmented impedance measuring method provided by the invention can realize segmented measurement of pregnant woman abdomen impedance, and provides technical support for abdomen impedance and body composition change analysis and fetal weight estimation during pregnancy.
(2) The fetal weight estimation method based on body composition (namely the abdominal segmented impedance of the pregnant woman) provided by the invention can realize fetal weight estimation in the pregnancy, does not need B-ultrasonic detection and uterine height measurement, and effectively reduces the cost and complexity of fetal weight estimation.
Drawings
Fig. 1a is a four-port network body distribution diagram in a pregnant woman abdomen segmented impedance measurement method, wherein R1 represents a first excitation electrode, R2 represents a first measurement electrode, R3 represents a second measurement electrode, and R4 represents a second excitation electrode;
FIG. 1b is a schematic diagram showing the current flowing through the human body when the first excitation electrode is excited by applying the current;
FIG. 1c is a schematic view showing the current flowing through the human body when the second excitation electrode is excited by applying the current;
FIG. 2 is a schematic flow chart of a method for estimating fetal weight according to an embodiment of the present invention;
FIG. 3 is a schematic flow chart of the method for estimating the fetal weight according to the present invention;
FIG. 4 is a graph showing the error between the predicted weight and the actual weight of a fetus according to the method for estimating fetal weight of the present invention;
fig. 5 shows the predicted body weight and the true value according to the optimal prediction model.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the drawings of the embodiments of the present invention. It is to be understood that the embodiments described are only a few embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the described embodiments of the invention, are within the scope of the invention.
The pregnant woman abdominal segmented impedance measuring method according to the embodiment of the invention is described in detail below with reference to the accompanying drawings.
The pregnant woman abdomen segmented impedance measuring method comprises the following steps of:
(1) and establishing a four-port network for pregnant woman abdomen segmented impedance measurement.
In the invention, the pregnant abdomen impedance measurement model adopts a four-port impedance network.
In order to reduce the influence caused by contact impedance between skin and electrodes and estimate the value of the abdominal impedance of a pregnant woman through measurement as few as possible, four-electrode bioelectrical impedance measurement is utilized. As shown in fig. 1 a-1 c, the four-port network includes two measurement electrodes and two excitation electrodes.
In one example of the invention, as shown in fig. 1a, the two measuring electrodes are a first measuring electrode R2 and a second measuring electrode R3, respectively, the first measuring electrode R2 connects the left and right waist of the pregnant woman, and the second measuring electrode R3 connects the waist of one side of the pregnant woman (the right side of fig. 1a, corresponding to the left side of the pregnant woman's actual body) with the hip of said one side. In addition, the two excitation electrodes are a first excitation electrode R1 and a second excitation electrode R4, respectively, the first excitation electrode R1 connects the waist of the other side of the pregnant woman with the hip of the other side (i.e., the side of the first excitation electrode R1 opposite to the second measurement electrode R3), and the second excitation electrode R4 connects the left hip and the right hip of the pregnant woman.
It should be noted that the above is only an example, for example, the position of the first excitation electrode R1 and the position of the second measurement electrode R3 may be exchanged, the position of the second excitation electrode R4 and the position of the first measurement electrode R2 may be exchanged, or the positions of the first excitation electrode R1 and the second measurement electrode R3, and the positions of the second excitation electrode R4 and the first measurement electrode R2 may be exchanged at the same time.
In the following description of the invention, the situation of fig. 1a to 1c is explained for the sake of simplicity. Those skilled in the art can perform impedance measurement of the abdomen of the pregnant woman based on the above-mentioned position exchange based on the following description, and such modifications are intended to fall within the scope of the present invention.
(2) And calculating the abdominal segmented impedance of the pregnant woman according to the four-port network.
Through the four-port network arranged above, the four-port network is excited by a first excitation electrode R1 (shown in fig. 1 b) and a second excitation electrode R4 (shown in fig. 1 c), and four sections of impedances corresponding to the first measuring electrode, the second measuring electrode, the first excitation electrode and the second excitation electrode are calculated.
In some embodiments of the present invention, a predetermined current is connected to two ends of the first excitation electrode R1 for excitation, and voltage differences between the first excitation electrode R1 and the first measurement electrode R2, the second measurement electrode R3, and the second excitation electrode R4 are measured; thereafter, the predetermined current is inputted to both ends of the second excitation electrode R4 for excitation, and the voltage difference between the second excitation electrode R4 and the first measurement electrode R2, the second measurement electrode R3, the first excitation electrode R1 is measured; finally, four sections of impedances corresponding to the first measuring electrode R2, the second measuring electrode R3, the first exciting electrode R1 and the second exciting electrode R4 are calculated according to the voltage differences measured between the first exciting electrode R1 and the first measuring electrode R2, the second measuring electrode R3 and the second exciting electrode R4 and the voltage differences measured between the second exciting electrode R4 and the first measuring electrode R2, the second measuring electrode R3 and the first exciting electrode R1.
Hereinafter, the calculation process of the abdomen segmental impedance of the pregnant woman will be described in detail with reference to the accompanying drawings.
Fig. 1b is a schematic diagram of the current flowing through the abdominal impedance when the ac (first excitation electrode R1) is switched on. Current flows through ab, bd, dc, and forms a parallel circuit with ac. At this time, three voltage values ab, bd and dc are measured respectively, so that the ratio of the corresponding impedances can be obtained through the ratio of the voltages.
When a current is switched on cd (second excitation electrode R4), as shown in fig. 1c, the current flows through ca, ab, bd and forms a parallel circuit with dc. At this time, the voltage values at ca, ab and bd are measured respectively, so that the ratio of the corresponding impedances can be obtained through the ratio of the voltages.
As can be seen from the measurement principle of the four-port circuit network, the correspondence of 6 pairs of active excitation-measurement ports can be obtained (see table 1).
TABLE 1 efficient stimulus-measurement Port mapping Table
Figure GDA0003171419020000111
When the ac port (i.e. two ends of the first excitation electrode R1) is connected with current excitation, as can be seen from fig. 1 b:
Figure GDA0003171419020000112
wherein, in the formula (1), the current I is added between the left waist part a and the left crotch part c, and the voltage between a and c is measured to be Vac-ac。
For easy solution, according to the circuit principle, when current flows through the same circuit, the ratio of voltage values at different ports is equal to the ratio of electrical impedance at the ports, and when current I is applied between the left waist a and the left crotch c, respectively at the measurement Vab、Vbd、VcdThree voltages, at which the resistance R is obtained2、R3、R4The three impedance values are as follows in equation (2).
Similarly, as shown in FIG. 1c, the excitation current is increased between c and d, and the equation (3) of the corresponding impedance is measured, which corresponds to the following equation:
Vac-ab:Vac-bd:Vac-cd＝R2:R3:R4 (2)
Vcd-ac:Vcd-ab:Vcd-bd＝R1:R2:R3 (3)
according to the above formulas (2) and (3):
Figure GDA0003171419020000113
further, by calculation, it is possible to obtain:
Figure GDA0003171419020000121
the above formula (5) is substituted into (1) to obtain:
Figure GDA0003171419020000122
furthermore, the values of the abdominal body impedance of the pregnant woman calculated by the formula (6) and the formula (5) are respectively:
Figure GDA0003171419020000123
Figure GDA0003171419020000124
Figure GDA0003171419020000125
the following can be obtained by simplifying the above equations (7), (8) and (9):
Figure GDA0003171419020000126
Figure GDA0003171419020000127
Figure GDA0003171419020000128
abdomen four-section impedance R1、R2、R3、R4Can be calculated by the above equations (10), (6), (11) and (12).
Next, a fetal weight estimation method according to an embodiment of the present invention will be described with reference to fig. 2 and 3.
As shown in fig. 2, the fetal weight estimation method according to the embodiment of the present invention includes the following steps:
A. first, the abdominal segment impedance of the pregnant woman is obtained.
Specifically, the calculation can be performed with reference to the above-described method.
B. And then, acquiring the equivalent abdominal impedance according to the abdominal segmented impedance.
For example, the calculation formula of the equivalent impedance is shown as follows:
Figure GDA0003171419020000131
wherein R isEquivalence ofRepresents the equivalent impedance, R1、R2、R3、R4Respectively representing four sections of impedance corresponding to the four-port network.
C. Next, a fetal weight estimation model is established based on the abdominal equivalent impedance.
Specifically, in the step B, the abdomen segmented impedance and the abdomen equivalent impedance in 2 different frequency bands are respectively calculated, and the fetal weight estimation model may be established according to the abdomen segmented impedance and the abdomen equivalent impedance in the different frequency bands.
The fetal weight estimation model is shown as follows:
Y＝78*(Ti-20)+(α*H*H)/R250 equivalent+(β*ΔW)/R500 equivalent (14)
Wherein Y is the weight of the fetus in grams,
h is the abdominal circumference of the pregnant woman in centimeters,
Δ W is the weight gain of pregnant women, the weight difference with the weight of the pregnant precursors during detection, and the unit is gram,
Tiin the case of the week of pregnancy,
R250 equivalent、R500 equivalentRespectively representing equivalent impedances in the 1 st band and the 2 nd band,
alpha and beta are reference coefficients.
Further, tests are performed for two samples, and the reference coefficients α and β are calculated from the test values. Wherein the reference coefficient α may be calculated by the following formula:
Figure GDA0003171419020000141
the reference coefficient β is calculated by the following formula:
Figure GDA0003171419020000142
wherein R is250、R500、Y、H、ΔW、TiAll the test data are the test data in the 1 st sample; r250'、R500'、Y'、H'、ΔW、TiThe test data in the 2 nd. It should be noted that, in order to make the formula simple, R is250 equivalentIs recorded as R250R is to be500 equivalentIs recorded as R500R is to be250 equivalent' Note R250', introduction of R500 equivalentIs recorded as R500′。
Further, in order to optimize the reference coefficients, a set of test samples may be selected, the fetal weight is estimated according to the calculated α and β values based on the actual maternal body parameters of the test samples, the estimated weight is compared with the actual weight of the test samples, two samples with the smallest error are selected to recalculate the reference coefficients α and β, and the fetal weight estimation model is established based on the recalculated α and β.
Next, the optimization of α and β will be described in detail with reference to fig. 3.
As shown in fig. 3, first, data is initialized, the sample is divided into a sample to be measured and a test sample (as shown in table 1 below), and the sample to be measured is combined two by two to form a data set L.
The first 10 groups in table 2 were used as samples to be tested, and the samples to be tested were combined two by two to estimate the fetal weight model. The last 3 groups served as test samples to test the accuracy of the model.
TABLE 2 data of B ultrasonic part and segmental impedance measurement part of abdomen in late pregnancy in different gestational weeks
Figure GDA0003171419020000151
The first 10 groups are samples to be tested, and the results of 45 types of alpha and beta groups can be obtained by combining the samples to be tested two by two (the combination of the sample 1 and the samples 2-10 is respectively recorded as combination 1-combination 9, the combination of the sample 2 and the samples 3-10 is respectively recorded as combination 10-combination 17, and the like). In the case of these 45 combinations, the optimum α and β combinations are found from the error between the predicted body weight and the actual body weight.
Specifically, first, a group of samples 1 and 2 in the sample data set L to be measured is selected, and the adjustable coefficients α and β are derived according to the prediction formula derived from S4 in embodiment 1, as follows:
Figure GDA0003171419020000152
wherein R is250、R500、Y、H、ΔW、TiAll the test data are the test data in the 1 st sample; r250'、R500'、Y'、H'、ΔW、TiFor the test data in item 2, R is added250 equivalentIs recorded as R250R is to be500 equivalentIs recorded as R500R is to be250 equivalent' Note R250', introduction of R500 equivalentIs recorded as R500′。
Then, the value of the corresponding alpha can be obtained according to the weight prediction formula:
Figure GDA0003171419020000161
then, the data in sample 1 and sample 2 are used to solve the corresponding α and β values, respectively. The solved alpha and beta values are then substituted into equations (14) to determine a fetal weight estimation model. And calculates a difference between the weight calculated according to the weight estimation model and the actual weight.
As described above, the values of alpha and beta were calculated at 45 combinations, respectively, and the results were taken in (14) to estimate the body weight. The error between the 45 combined specific weight estimates and the actual weight is shown in figure 4. In the case of these 45 combinations, the optimum α and β combinations are found from the error between the predicted body weight and the actual body weight, and the body weight estimation model equation (14) is determined using the optimum α and β combinations.
Thereafter, the test sample 11 is substituted into the above-identified equation (14), and the fetal weight estimation is performed.
Similarly, the test samples 12, 13 are also individually subjected to fetal weight estimation.
Thereafter, the values of α and β are recalculated in order of magnitude of error, with the two sets of test samples having the smallest error.
Fetal weight estimation models are applicable to late and mid-term pregnancy, especially TiIs more than or equal to 25, namely is especially suitable for estimating the weight of the fetus after 25 weeks.
D. And finally, calculating the fetal weight according to the fetal weight estimation model and the physical parameters of the pregnant woman.
After the fetal weight estimation model is determined, the fetal weight is calculated based on the fetal weight estimation model and physical parameters of the pregnant woman (abdominal circumference of the pregnant woman, weight gain of the pregnant woman, and gestational week).
The fetal weight was estimated based on the optimized α and β values and the fetal weight estimation model, and the results are shown in fig. 5.
While the foregoing is directed to the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.

Claims (9)

1. A method of estimating fetal weight, comprising the steps of:
establishing a four-port network for pregnant woman abdominal section impedance measurement;
calculating the abdominal segmented impedance of the pregnant woman according to the four-port network;
obtaining the equivalent impedance of the abdomen according to the segmented impedance of the abdomen;
establishing a fetal weight estimation model according to the abdominal equivalent impedance;
calculating the fetal weight according to the fetal weight estimation model and the physical parameters of the pregnant woman;
respectively calculating abdominal segmented impedance and abdominal equivalent impedance under 2 different frequency bands, and establishing the fetal weight estimation model according to the abdominal segmented impedance and the abdominal equivalent impedance under the different frequency bands;
the calculation formula of the equivalent impedance is shown as the following formula:
Figure FDA0003135967890000011
wherein R isEquivalence ofRepresents the equivalent impedance, R1、R2、R3、R4Respectively representing four sections of impedance corresponding to the four-port network.
2. The fetal weight estimation method of claim 1, wherein the four-port network comprises two measurement electrodes and two excitation electrodes.
3. The fetal weight estimation method of claim 2, wherein the two measuring electrodes are a first measuring electrode and a second measuring electrode, respectively, the first measuring electrode connecting the left and right waists of the pregnant woman, the second measuring electrode connecting the one waist and the hip of the one side of the pregnant woman;
the two excitation electrodes are respectively a first excitation electrode and a second excitation electrode, the first excitation electrode is connected with the waist of the other side of the pregnant woman and the hip of the other side of the pregnant woman, and the second excitation electrode is connected with the left hip and the right hip of the pregnant woman.
4. The fetal weight estimation method of claim 3, wherein the four-port network is excited by the first excitation electrode and the second excitation electrode to calculate four sections of impedance corresponding to the first measuring electrode, the second measuring electrode, the first excitation electrode and the second excitation electrode, respectively.
5. The fetal weight estimation method of claim 4, wherein a predetermined current is applied to both ends of the first excitation electrode for excitation, and voltage differences between the first excitation electrode and the first measuring electrode, the second measuring electrode and the second excitation electrode are measured,
inputting the predetermined current to two ends of the second excitation electrode for excitation, and measuring the voltage difference between the second excitation electrode and the first measuring electrode, the second measuring electrode and the first excitation electrode,
and calculating four sections of impedances corresponding to the first measuring electrode, the second measuring electrode, the first exciting electrode and the second exciting electrode according to the voltage differences between the first exciting electrode and the first measuring electrode, the second measuring electrode and the second exciting electrode and the voltage differences between the second exciting electrode and the first measuring electrode, the second measuring electrode and the first exciting electrode.
6. The method of claim 1, wherein the fetal weight estimation model is as follows:
Y＝78*(Ti-20)+(α*H*H)/R250 equivalent+(β*ΔW)/R500 equivalent
Wherein Y is the weight of the fetus in grams,
h is the abdominal circumference of the pregnant woman in centimeters,
Δ W is the weight gain of pregnant women, the weight difference with the weight of the pregnant precursors during detection, and the unit is gram,
Tiin the case of the week of pregnancy,
R250 equivalent、R500 equivalentRespectively representing equivalent impedances in the 1 st band and the 2 nd band,
alpha and beta are reference coefficients.
7. The fetal weight estimation method of claim 6, wherein a test is performed on two samples and the reference coefficients a and β are calculated from the test values, wherein,
the reference coefficient α is calculated by the following formula:
Figure FDA0003135967890000031
the reference coefficient β is calculated by the following formula:
Figure FDA0003135967890000032
wherein R is250、R500、Y、H、ΔW、TiAll the test data are the test data in the 1 st sample; r250′、R500′、Y′、H′、△W′、Ti' for the test data in sample 2, R250 equivalentIs recorded as R250R is to be500 equivalentIs recorded as R500R is to be250 equivalent' Note R250', introduction of R500 equivalent' Note R500′。
8. The method of claim 7, wherein a set of test samples is selected, the fetal weight is estimated according to the determined values of α and β based on the actual maternal body parameters of the test samples, the estimated weight is compared with the actual weight of the test samples, the reference coefficients α and β are recalculated using two samples with the smallest error, and the model of fetal weight estimation is established based on the recalculated values of α and β.
9. The fetal weight estimation method of claim 6, wherein T isiGreater than or equal to 25.
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