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Does fetal heart rate predict subsequent heart rate in childhood?
Early Human Development, 19 (1989) 147-152 Elsevier Scientific Publishers Ireland Ltd.
147
EHD 00978
Does fetal heart rate predict subsequent heart rate in childhood? Peter W. Thomas, Mary N. Haslum, Ian MacGillivray and M. Jean Golding Institute of Child Health, Royal Hospitalfor Sick Children, Bristol BS2 BBJ(U.K.) Accepted for publication 17 January 1989
Summary An investigation to determine whether there is any relationship between extremes of fetal heart rate during labour and subsequent heart rate at the age of 10 was carried out using data from the 1970 cohort of British Births. In 11,000 nationally representative children it was found that low fetal heart rate (below 120 beats/min) was associated with a heart rate at age 10 which was significantly lower than in those children whose fetal heart rate had remained between 120 and 160 beats/min (Z’< 0.01). This relationship could not be explained by fetal asphyxiation, maternal antenatal hypotension or the method of pain relief during labour. There was no equivalent relationship with high fetal heart rate during labour. This could imply that some fetuses with low heart rates are not exhibiting fetal distress but have an inherent tendency to relatively slow heart rates. fetal; heart rate; childhood; measurements.
Introduction Monitoring fetal heart rate intrapartum has for many years been standard practice in hospitals in the UK. High fetal heart rate (tachycardia) may commonly reflect maternal or fetal infection, prematurity, maternal bleeding or maternal tachycardia [3]. Low fetal heart rate (bradycardia) may be an indicator of fetal
Correspondence to: Jean Gelding. 0378-3782/89/$03.50 0 1989 Elsevier Scientific Publishers Ireland Ltd. Published and Printed in Ireland
148
asphyxiation or be due to anaesthetics given to the mother [3]. There is, therefore, a higher incidence of morbidity and mortality in infants who showed abnormal fetal heart rates [4]. Here we address the question of whether there are more subtle longterm associations. Materials and methods The 1970 British Births Survey is a study of all children born in Great Britain between the 5th and 1lth April 1970. After the delivery of each child a questionnaire was completed by the midwife who was responsible for the birth. In this way information on each mother’s social and medical background, antenatal visits, labour and delivery and the well being of her child in the perinatal period were collected. This information included whether during labour the fetal heart rate (a) remained between 120 and 160 beats/mm, (b) rose above 160 beats/min or (c) fell below 120 beats/min. A total of 17,196 questionnaires were completed and returned [ 11. At the age of 10 years, 14 906 of the children (94% of those surviving the birth cohort and thought to be resident in Great Britain) were followed-up. This time the mother was interviewed again and extensive educational tests were carried out on the child. Of these children, 13,723 were also examined by a Clinical Medical Officer who took a medical history and made a general and systemic examination (which included a number of motor coordination tests). Pulse rate was measured for each child at the beginning of the examination, blood pressure half way through the examination and pulse rate was measured again at the end of the examination. On each occasion that the pulse rate was measured, the medical officer was instructed to settle the child for at least 2 min beforehand and to take the pulse over a period of a minute. Each medical examination lasted for approximately 25 min and the medical officer was not aware of the fetal heart rate measurements. For 11,190 children, information both on the intrapartum fetal heart rate and on the two pulse rates at 10 years were available. These data have been analysed using simple linear regression in order to calculate differences in mean pulse rates (regression coefficients) between the group whose fetal heart rate remained between 120 and 160 beats/min during labour (base group) and the groups who experienced abnormal fetal heart rates during labour. When trying to explain this relationship by adjusting for other factors, multiple linear regression has been used. Results For those children in the Birth Survey who were followed-up at the age of 10, the distribution of fetal heart rates is shown in Table Ia and that of pulse rates taken at the age of 10 is shown in Table Ib. The mean pulse rate taken at the beginning of the medical examination was significantly higher than that taken at the end (P < 0.001). In 12.3% of children pulse rate remained the same throughout the examination, in 49.3% of children pulse rate fell and in 38.3% it rose. Approximately 13% of children had a fall in pulse rate of 10 beats/min or more. To investigate whether fetal heart rate was related to childhood heart rate, the
149 TABLE I Frequency distributions of fetal heart rates and childhood pulse rates. (a) Fetal heart rates during labour. Fetal heart rate (beats/mitt)
Frequency (Vo)
Remained between 120 and 160 throughout Fell below 120 Rose above 160 Both fell and rose
10 809 (92.1) 607 (5.2) 282 (2.4) 37 (0.3)
Total
11735 (100)
(b) Pulse rates at 10 years old. Pulse rate (beats/mm)
Frequency <60 60-69 70-79 SO-89 90-99
100-109 110+ Total Mean SD.
End of examination
Start of examination
124 1357 3661 4335 1728 673 192 12070 81.33 11.26
Frequency
70
1.0
11.2 30.3 35.9 14.3 5.6 1.6 100
070
185 1470 3960 4197 1492 539 157
1.5 12.3 33.0 35.0 12.4 4.5 1.3
12ooo 80.22 11.06
100
first pulse rate, second pulse rate and the difference between the two pulse rates (first pulse rate - second pulse rate) were adjusted for fetal heart rate by using simple linear regression. The results are presented in Table II and show that abnormal fetal heart was not significantly related to either the first pulse rate or the difference in pulse rates. However, children whose fetal heart rate had fallen below 120 beats/ min tended to have, at the age of 10 years old, a mean second pulse rate that was 1.41 beats/min lower than children who had had a normal fetal heart rate (P < 0.001). Excluding children with a serious congenital abnormality (mongolism, spina bifida, hydrocephalus or a diagnosed or suspected congenital heart condition) from the analysis in Table II made little difference to the regression coefficients. Asphyxiation is known to be a major cause of a drop in fetal heart rate. For the purposes of this study asphyxiation was defined as occurring when the time to establish regular respirations after delivery exceeded 3 min. Of those infants who were followed up at age 10, 439 (3.9%) had been asphyxiated and of these 60 (13.7%) were known to have had a fetal heart rate which fell below 120 beats/min compared
150 TABLE II Results of regression of pulse rates on fetal heart rates. Fetal heart rate (relative to normal)
First pulse rate
Second pulse rate
Difference between First and second pulse rates
P
SE.
Sigh
P
SE.
Sigh
b’
S.E.
Sigh
-0.94 -0.09 0.55
0.48 0.70 1.89
NS NS NS
- 1.41 - 0.32 1.16
0.47 0.69 1.85
** NS NS
0.41 0.16 - 0.62
0.36 0.52 1.40
NS NS NS
< 120 >160 Both
’Regression coefficients (difference in mean pulse rates at age 10 in this group from group who had a normal fetal heart rate during labour). bSignificance level obtained by testing hypothesis that b = 0. NS, P > 0.05; **P< 0.01.
with only 4.8% of the 10,855 infants who had not been asphyxiated. Therefore the regression analysis of pulse rate on fetal heart rate was repeated separately for asphyxiated and non-asphyxiated fetuses (Table III). The relationship between a fall in fetal heart rate to below 120 beats/min and the second pulse rate at 10 years old was still apparent both for non-asphyxiated and for asphyxiated fetuses; the regression coefficients were of a similar magnitude, but the relationship within the small asphyxiated group was not statistically significant. There was no significant difference in mean pulse rates (k SE.) at age 10 between TABLE III Results of regression of second pulse rate on fetal heart rate for asphyxiated and non-asphyxiated fetuses.
Fetal heart rate (relative to normal)
Second pulse rate
&
(A) Non-asphyxiated < 120 >160 Both (B) Asphyxiated <120 >I60 Both
S.E.
Sigh
- 1.55
0.54
**
0.61 1.36
0.81 2.39
NS NS
- 1.75 - 2.34 - 1.51
2.03 2.25 4.91
NS NS NS
‘b regression coefficient (see footnote for Table II). bSee footnote for Table II.
151
the group who had been asphyxiated (80.87 f 0.68) and the group who had not (80.15 f 0.12). The relationship between a fall in fetal heart rate to below 120 beats/min and a low mean second pulse rate for children who had not been asphyxiated was still apparent after using multiple linear regression to adjust for whether the mother had been given inhalation analgesia, opiates, drugs other than opiates, general anaesthetic, anaesthetic other than general, or whether she had a highest antenatal diastolic blood pressure under 80 mmHg. Discussion We have shown that a fall in fetal heart rate to below 120 beats/min during labour is associated with the second (but not the first) of two recordings of pulse rate measured by a Clinical Medical Officer when the child was 10 years old. On average, the pulse rates in the group of children who had had a fall in fetal heart rate were 1.4 beats/min lower than in the group whose fetal heart rate had been normal during labour. The differences between first and second pulse rates during the 10 year medical examination are possibly due to different physiological reactions to the stresses associated with such an examination. In almost half the children the first pulse rate was higher than the second; the elevated first pulse rate was probably due to anxiety about facing a medical examination. However, 38% of the children experienced a rise in pulse rate indicating that they may have been becoming more anxious as the examination progressed. To determine if the fall in fetal heart rate during labour had a role in determining ‘unstressed’, but not ‘stressed’ pulse rate at the age of 10, the data was re-analysed using firstly the lowest (‘unstressed’) and then the highest (‘stressed’) of the two pulse rates. The results showed that children whose fetal heart rate fell below 120 beats/min had, on average, a lower ‘unstressed’ pulse rate (b = - 1.33, P = 0.004) and also a lower ‘stressed’ pulse rate (b = - 1.29, P = 0.011). One can hypothesise that the fetal characteristics associated with low fetal heart rate during labour have played, or indeed, are still playing a role in determining heart rate at the age of 10 years. However, none of the characteristics that we have explored herein, have explained the relationship between low fetal heart rate and pulse rate. There has been much evidence published recently to support the notion that tracking for blood pressure (the tendency for individuals to remain at the same position in the distribution of blood pressures regardless of age) in adults begins in childhood, and that this phenomenon may start as early as 4 days of age [2]. From the evidence presented here, the same may also be true of heart rates. Further exploration of this hypothesis will obviously need to use a rather less crude measure of fetal heart rate than was available to this study. Acknowledgements We are very grateful to all the health personnel involved in the Child Health and Education Study, particularly the midwives and health visitors who collected the
152
data, and to the mothers and children for their cooperation. The 1970 birth survey was carried out under the joint auspices of the National Birthday Trust Fund and the Royal College of Obstetricians and Gynaecologists, the 5 year follow-up by the MRC and the 10 year follow-up by the D.H.S.S. and the D.E.S. These particular analyses were funded by the British Heart Foundation. Dr. Golding is a Wellcome Senior Lecturer. We would also like to thank Yasmin Iles for the typing of this manuscript. References 1 Chamberlain, G., Philip, E., Howlett, B. and Masters, K. (1978) British Births 1970, Volume 2: Obstetric Care. Heinemann Medical Books, London. 2 DeSwiet, M., Fayers, P. and Shineboume. E.A. (1980) Value of repeated blood pressure measurements in children - the Brompton Study. Br. Med. J., 2: 1567-1569. 3 Flynn, A.M. and Kelly, J. (1982) Fetal monitoring in labour. In: Recent Advances in Obstetrics and Gynaecology, No. 14. Editor: J. Bonnar. Churchill Livingstone, Edinburgh. 4 Phillips, W.D.P. and Towell, M.E. (1980) Abnormal fetal heart rate assoicated with congenital abnormalities. Br. J. Obstet. Gynaecol., 87.270-274.
147
EHD 00978
Does fetal heart rate predict subsequent heart rate in childhood? Peter W. Thomas, Mary N. Haslum, Ian MacGillivray and M. Jean Golding Institute of Child Health, Royal Hospitalfor Sick Children, Bristol BS2 BBJ(U.K.) Accepted for publication 17 January 1989
Summary An investigation to determine whether there is any relationship between extremes of fetal heart rate during labour and subsequent heart rate at the age of 10 was carried out using data from the 1970 cohort of British Births. In 11,000 nationally representative children it was found that low fetal heart rate (below 120 beats/min) was associated with a heart rate at age 10 which was significantly lower than in those children whose fetal heart rate had remained between 120 and 160 beats/min (Z’< 0.01). This relationship could not be explained by fetal asphyxiation, maternal antenatal hypotension or the method of pain relief during labour. There was no equivalent relationship with high fetal heart rate during labour. This could imply that some fetuses with low heart rates are not exhibiting fetal distress but have an inherent tendency to relatively slow heart rates. fetal; heart rate; childhood; measurements.
Introduction Monitoring fetal heart rate intrapartum has for many years been standard practice in hospitals in the UK. High fetal heart rate (tachycardia) may commonly reflect maternal or fetal infection, prematurity, maternal bleeding or maternal tachycardia [3]. Low fetal heart rate (bradycardia) may be an indicator of fetal
Correspondence to: Jean Gelding. 0378-3782/89/$03.50 0 1989 Elsevier Scientific Publishers Ireland Ltd. Published and Printed in Ireland
148
asphyxiation or be due to anaesthetics given to the mother [3]. There is, therefore, a higher incidence of morbidity and mortality in infants who showed abnormal fetal heart rates [4]. Here we address the question of whether there are more subtle longterm associations. Materials and methods The 1970 British Births Survey is a study of all children born in Great Britain between the 5th and 1lth April 1970. After the delivery of each child a questionnaire was completed by the midwife who was responsible for the birth. In this way information on each mother’s social and medical background, antenatal visits, labour and delivery and the well being of her child in the perinatal period were collected. This information included whether during labour the fetal heart rate (a) remained between 120 and 160 beats/mm, (b) rose above 160 beats/min or (c) fell below 120 beats/min. A total of 17,196 questionnaires were completed and returned [ 11. At the age of 10 years, 14 906 of the children (94% of those surviving the birth cohort and thought to be resident in Great Britain) were followed-up. This time the mother was interviewed again and extensive educational tests were carried out on the child. Of these children, 13,723 were also examined by a Clinical Medical Officer who took a medical history and made a general and systemic examination (which included a number of motor coordination tests). Pulse rate was measured for each child at the beginning of the examination, blood pressure half way through the examination and pulse rate was measured again at the end of the examination. On each occasion that the pulse rate was measured, the medical officer was instructed to settle the child for at least 2 min beforehand and to take the pulse over a period of a minute. Each medical examination lasted for approximately 25 min and the medical officer was not aware of the fetal heart rate measurements. For 11,190 children, information both on the intrapartum fetal heart rate and on the two pulse rates at 10 years were available. These data have been analysed using simple linear regression in order to calculate differences in mean pulse rates (regression coefficients) between the group whose fetal heart rate remained between 120 and 160 beats/min during labour (base group) and the groups who experienced abnormal fetal heart rates during labour. When trying to explain this relationship by adjusting for other factors, multiple linear regression has been used. Results For those children in the Birth Survey who were followed-up at the age of 10, the distribution of fetal heart rates is shown in Table Ia and that of pulse rates taken at the age of 10 is shown in Table Ib. The mean pulse rate taken at the beginning of the medical examination was significantly higher than that taken at the end (P < 0.001). In 12.3% of children pulse rate remained the same throughout the examination, in 49.3% of children pulse rate fell and in 38.3% it rose. Approximately 13% of children had a fall in pulse rate of 10 beats/min or more. To investigate whether fetal heart rate was related to childhood heart rate, the
149 TABLE I Frequency distributions of fetal heart rates and childhood pulse rates. (a) Fetal heart rates during labour. Fetal heart rate (beats/mitt)
Frequency (Vo)
Remained between 120 and 160 throughout Fell below 120 Rose above 160 Both fell and rose
10 809 (92.1) 607 (5.2) 282 (2.4) 37 (0.3)
Total
11735 (100)
(b) Pulse rates at 10 years old. Pulse rate (beats/mm)
Frequency <60 60-69 70-79 SO-89 90-99
100-109 110+ Total Mean SD.
End of examination
Start of examination
124 1357 3661 4335 1728 673 192 12070 81.33 11.26
Frequency
70
1.0
11.2 30.3 35.9 14.3 5.6 1.6 100
070
185 1470 3960 4197 1492 539 157
1.5 12.3 33.0 35.0 12.4 4.5 1.3
12ooo 80.22 11.06
100
first pulse rate, second pulse rate and the difference between the two pulse rates (first pulse rate - second pulse rate) were adjusted for fetal heart rate by using simple linear regression. The results are presented in Table II and show that abnormal fetal heart was not significantly related to either the first pulse rate or the difference in pulse rates. However, children whose fetal heart rate had fallen below 120 beats/ min tended to have, at the age of 10 years old, a mean second pulse rate that was 1.41 beats/min lower than children who had had a normal fetal heart rate (P < 0.001). Excluding children with a serious congenital abnormality (mongolism, spina bifida, hydrocephalus or a diagnosed or suspected congenital heart condition) from the analysis in Table II made little difference to the regression coefficients. Asphyxiation is known to be a major cause of a drop in fetal heart rate. For the purposes of this study asphyxiation was defined as occurring when the time to establish regular respirations after delivery exceeded 3 min. Of those infants who were followed up at age 10, 439 (3.9%) had been asphyxiated and of these 60 (13.7%) were known to have had a fetal heart rate which fell below 120 beats/min compared
150 TABLE II Results of regression of pulse rates on fetal heart rates. Fetal heart rate (relative to normal)
First pulse rate
Second pulse rate
Difference between First and second pulse rates
P
SE.
Sigh
P
SE.
Sigh
b’
S.E.
Sigh
-0.94 -0.09 0.55
0.48 0.70 1.89
NS NS NS
- 1.41 - 0.32 1.16
0.47 0.69 1.85
** NS NS
0.41 0.16 - 0.62
0.36 0.52 1.40
NS NS NS
< 120 >160 Both
’Regression coefficients (difference in mean pulse rates at age 10 in this group from group who had a normal fetal heart rate during labour). bSignificance level obtained by testing hypothesis that b = 0. NS, P > 0.05; **P< 0.01.
with only 4.8% of the 10,855 infants who had not been asphyxiated. Therefore the regression analysis of pulse rate on fetal heart rate was repeated separately for asphyxiated and non-asphyxiated fetuses (Table III). The relationship between a fall in fetal heart rate to below 120 beats/min and the second pulse rate at 10 years old was still apparent both for non-asphyxiated and for asphyxiated fetuses; the regression coefficients were of a similar magnitude, but the relationship within the small asphyxiated group was not statistically significant. There was no significant difference in mean pulse rates (k SE.) at age 10 between TABLE III Results of regression of second pulse rate on fetal heart rate for asphyxiated and non-asphyxiated fetuses.
Fetal heart rate (relative to normal)
Second pulse rate
&
(A) Non-asphyxiated < 120 >160 Both (B) Asphyxiated <120 >I60 Both
S.E.
Sigh
- 1.55
0.54
**
0.61 1.36
0.81 2.39
NS NS
- 1.75 - 2.34 - 1.51
2.03 2.25 4.91
NS NS NS
‘b regression coefficient (see footnote for Table II). bSee footnote for Table II.
151
the group who had been asphyxiated (80.87 f 0.68) and the group who had not (80.15 f 0.12). The relationship between a fall in fetal heart rate to below 120 beats/min and a low mean second pulse rate for children who had not been asphyxiated was still apparent after using multiple linear regression to adjust for whether the mother had been given inhalation analgesia, opiates, drugs other than opiates, general anaesthetic, anaesthetic other than general, or whether she had a highest antenatal diastolic blood pressure under 80 mmHg. Discussion We have shown that a fall in fetal heart rate to below 120 beats/min during labour is associated with the second (but not the first) of two recordings of pulse rate measured by a Clinical Medical Officer when the child was 10 years old. On average, the pulse rates in the group of children who had had a fall in fetal heart rate were 1.4 beats/min lower than in the group whose fetal heart rate had been normal during labour. The differences between first and second pulse rates during the 10 year medical examination are possibly due to different physiological reactions to the stresses associated with such an examination. In almost half the children the first pulse rate was higher than the second; the elevated first pulse rate was probably due to anxiety about facing a medical examination. However, 38% of the children experienced a rise in pulse rate indicating that they may have been becoming more anxious as the examination progressed. To determine if the fall in fetal heart rate during labour had a role in determining ‘unstressed’, but not ‘stressed’ pulse rate at the age of 10, the data was re-analysed using firstly the lowest (‘unstressed’) and then the highest (‘stressed’) of the two pulse rates. The results showed that children whose fetal heart rate fell below 120 beats/min had, on average, a lower ‘unstressed’ pulse rate (b = - 1.33, P = 0.004) and also a lower ‘stressed’ pulse rate (b = - 1.29, P = 0.011). One can hypothesise that the fetal characteristics associated with low fetal heart rate during labour have played, or indeed, are still playing a role in determining heart rate at the age of 10 years. However, none of the characteristics that we have explored herein, have explained the relationship between low fetal heart rate and pulse rate. There has been much evidence published recently to support the notion that tracking for blood pressure (the tendency for individuals to remain at the same position in the distribution of blood pressures regardless of age) in adults begins in childhood, and that this phenomenon may start as early as 4 days of age [2]. From the evidence presented here, the same may also be true of heart rates. Further exploration of this hypothesis will obviously need to use a rather less crude measure of fetal heart rate than was available to this study. Acknowledgements We are very grateful to all the health personnel involved in the Child Health and Education Study, particularly the midwives and health visitors who collected the
152
data, and to the mothers and children for their cooperation. The 1970 birth survey was carried out under the joint auspices of the National Birthday Trust Fund and the Royal College of Obstetricians and Gynaecologists, the 5 year follow-up by the MRC and the 10 year follow-up by the D.H.S.S. and the D.E.S. These particular analyses were funded by the British Heart Foundation. Dr. Golding is a Wellcome Senior Lecturer. We would also like to thank Yasmin Iles for the typing of this manuscript. References 1 Chamberlain, G., Philip, E., Howlett, B. and Masters, K. (1978) British Births 1970, Volume 2: Obstetric Care. Heinemann Medical Books, London. 2 DeSwiet, M., Fayers, P. and Shineboume. E.A. (1980) Value of repeated blood pressure measurements in children - the Brompton Study. Br. Med. J., 2: 1567-1569. 3 Flynn, A.M. and Kelly, J. (1982) Fetal monitoring in labour. In: Recent Advances in Obstetrics and Gynaecology, No. 14. Editor: J. Bonnar. Churchill Livingstone, Edinburgh. 4 Phillips, W.D.P. and Towell, M.E. (1980) Abnormal fetal heart rate assoicated with congenital abnormalities. Br. J. Obstet. Gynaecol., 87.270-274.