Neuropsychologio. Vol. 29, No. 11, pp. 1107-1111, 1991 Printed m Great Bntain.
C028-3932191 $3.00+0.00 ‘i; 1991 Pergamon Press plc
HANDEDNESS
IN THE HUMAN FETUS
PETER G. HEPPER,*~ SARA SHAHIDULLAH~~ and RAYMOND WHITE:: jSchoo1 of Psychology
and JDepartment of Obstetrics and Gynaecology, Belfast BT7 INN, Northern Ireland
The Queen’s University
of Belfast,
(Received 28 January 1991; accepted 15 July 1991)
Abstract-The developmental origins of behavioural asymmetries, in particular
handedness, have aroused considerable interest and debate. Until now such behavioural asymmetries have only been reported after birth. Here we report the existence of handedness before birth, expressed in terms of thumb-sucking by the fetus. Ultrasound observations of fetuses from 15 weeks to term revealed a marked bias for sucking the thumb of the right hand. This preference appears to be maintained throughout pregnancy, is unrelated to fetal position in utero but correlates with head position preference in the supine newborn. The findings indicate that handedness is present prior to birth and the implications of this for the development of laterality are discussed.
INTRODUCTION APPROXIMATELY10% of humans exhibit a bias for their left hand, the vast majority however exhibit a preference for their right hand [lS]. A number of theories have been proposed to explain this bias [lo], and debate has concentrated on whether this right-hand bias is a result of genetic factors (for example the right-shift theory of Annett [ 11) or experiential factors, and whether left-handedness results from some developmental (prenatal/birth) pathology [2,20]. Although handedness per se only becomes apparent during infancy as the infant’s motor abilities develop [ll], early indications of handedness or motor bias have been sought in the newborn by examining head position. Numerous studies have demonstrated that newborns prefer to lie with their head turned to the right and show a bias for turning their head right after first having it held in the midline position (e.g. Refs. [S-lo]). Behavioural or motor asymmetries have not been observed prior to birth. The advent of real-time ultrasound enables the non-invasive study of the fetus and its behaviour [12]. One of the many behaviours exhibited by the fetus which can be clearly observed is that of thumb-sucking, i.e. the fetus’s thumb is present in its mouth [12], and this presents the opportunity of assessing handedness before birth. It would be expected that if asymmetries are present before birth, observations of fetal thumb-sucking would demonstrate a preference for sucking the right thumb. Furthermore, if this is a reflection of later handedness, fetal thumb-sucking preference should correlate with head-turning preference in the individual after birth. Finally, it has been argued that head position after birth reflects the intrauterine orientation of the fetus and that this may be a determining factor in later hand preference [9, 161, thus the uterine position of the fetus was examined with respect to the thumb being sucked.
*To whom all correspondence
should
be addressed. 1107
1108
P. G. HEPPER, S. SHAHIDLJLLAHand R. WHITE
METHOD Subjects Over a 2-year period (August 1988-August 1990) observations were made on mothers attending the Royal Maternity Hospital, Belfast for routine clinical visits or as part of an on-going research programme examining fetal behaviour. In all, 282 fetuses were observed, all from normal, uncomplicated singleton pregnancies. The fetuses were divided into four groups dependent upon their gestational age; 12-15 weeks gestational age (n=8), 15-21 weeks gestational age (n = 81), 28-34 weeks gestational age (n =92) and 36 weeks gestational age to term (n = 101). Ninetyseven observations were made from routine clinical visits and 185 as part of the research programme. Twenty fetuses were observed sucking their thumb on three different occasions, each separated by at least 3 weeks. Of the 101 fetuses observed at 36 weeks gestational age-term, 32 were followed up as newborns (24 days of age) when their head-turning preference was examined. Procedure All fetuses were observed by real-time ultrasound for approx. 15 min and if the fetus was observed sucking its thumb, the thumb being sucked (left or right) was noted. Thumb-sucking was defined as observing the thumb present in the mouth of the fetus and simultaneous mouth movements. In all cases only a single bout of thumbsucking was observed during the observation period. Observations were performed by the authors or fully qualified radiographers. In most cases two observers were present and served to verify the observation of thumb-sucking. In the main analysis reported below each fetus contributed a single data point. For the 20 fetuses observed three times only the first observation is used in this analysis. Thus the 274 observations reported represent 274 different fetuses. For 50 fetuses at 32-38 weeks of gestational age their position right (either right occiput anterior or transverse) or left (either left occiput anterior or transverse) in the womb was noted as well as the thumb being sucked. Observations on neonates are reported for individuals delivered at 3841 weeks. All were fully developed with Apgar scores of greater than 7. Newborn head position preferences were determined 24 days after birth. All infants were awake at the time of testing and not crying. Individuals were tested in their own cots whilst lying on their backs. The infant’s head was held in the midline position until no pressure was felt on the examiner’s hand and then let go. The side to which the infant turned its head was noted by the examiner. An infant was classified as having turned its head to either right or left when its head position deviated 30 degrees or more from the midline. All infants turned their head well within the allotted IO-min observation period. Care was taken to ensure that there were no lateral sources of stimulation which could influence the turning preference.
RESULTS Fetal thumb-sucking In 274 separate pregnancies, fetuses were observed sucking their thumb (see Table 1). Binomial tests [21] revealed a clear bias for sucking the thumb of the right hand, in total (z=13.834, P
C028-3932191 $3.00+0.00 ‘i; 1991 Pergamon Press plc
HANDEDNESS
IN THE HUMAN FETUS
PETER G. HEPPER,*~ SARA SHAHIDULLAH~~ and RAYMOND WHITE:: jSchoo1 of Psychology
and JDepartment of Obstetrics and Gynaecology, Belfast BT7 INN, Northern Ireland
The Queen’s University
of Belfast,
(Received 28 January 1991; accepted 15 July 1991)
Abstract-The developmental origins of behavioural asymmetries, in particular
handedness, have aroused considerable interest and debate. Until now such behavioural asymmetries have only been reported after birth. Here we report the existence of handedness before birth, expressed in terms of thumb-sucking by the fetus. Ultrasound observations of fetuses from 15 weeks to term revealed a marked bias for sucking the thumb of the right hand. This preference appears to be maintained throughout pregnancy, is unrelated to fetal position in utero but correlates with head position preference in the supine newborn. The findings indicate that handedness is present prior to birth and the implications of this for the development of laterality are discussed.
INTRODUCTION APPROXIMATELY10% of humans exhibit a bias for their left hand, the vast majority however exhibit a preference for their right hand [lS]. A number of theories have been proposed to explain this bias [lo], and debate has concentrated on whether this right-hand bias is a result of genetic factors (for example the right-shift theory of Annett [ 11) or experiential factors, and whether left-handedness results from some developmental (prenatal/birth) pathology [2,20]. Although handedness per se only becomes apparent during infancy as the infant’s motor abilities develop [ll], early indications of handedness or motor bias have been sought in the newborn by examining head position. Numerous studies have demonstrated that newborns prefer to lie with their head turned to the right and show a bias for turning their head right after first having it held in the midline position (e.g. Refs. [S-lo]). Behavioural or motor asymmetries have not been observed prior to birth. The advent of real-time ultrasound enables the non-invasive study of the fetus and its behaviour [12]. One of the many behaviours exhibited by the fetus which can be clearly observed is that of thumb-sucking, i.e. the fetus’s thumb is present in its mouth [12], and this presents the opportunity of assessing handedness before birth. It would be expected that if asymmetries are present before birth, observations of fetal thumb-sucking would demonstrate a preference for sucking the right thumb. Furthermore, if this is a reflection of later handedness, fetal thumb-sucking preference should correlate with head-turning preference in the individual after birth. Finally, it has been argued that head position after birth reflects the intrauterine orientation of the fetus and that this may be a determining factor in later hand preference [9, 161, thus the uterine position of the fetus was examined with respect to the thumb being sucked.
*To whom all correspondence
should
be addressed. 1107
1108
P. G. HEPPER, S. SHAHIDLJLLAHand R. WHITE
METHOD Subjects Over a 2-year period (August 1988-August 1990) observations were made on mothers attending the Royal Maternity Hospital, Belfast for routine clinical visits or as part of an on-going research programme examining fetal behaviour. In all, 282 fetuses were observed, all from normal, uncomplicated singleton pregnancies. The fetuses were divided into four groups dependent upon their gestational age; 12-15 weeks gestational age (n=8), 15-21 weeks gestational age (n = 81), 28-34 weeks gestational age (n =92) and 36 weeks gestational age to term (n = 101). Ninetyseven observations were made from routine clinical visits and 185 as part of the research programme. Twenty fetuses were observed sucking their thumb on three different occasions, each separated by at least 3 weeks. Of the 101 fetuses observed at 36 weeks gestational age-term, 32 were followed up as newborns (24 days of age) when their head-turning preference was examined. Procedure All fetuses were observed by real-time ultrasound for approx. 15 min and if the fetus was observed sucking its thumb, the thumb being sucked (left or right) was noted. Thumb-sucking was defined as observing the thumb present in the mouth of the fetus and simultaneous mouth movements. In all cases only a single bout of thumbsucking was observed during the observation period. Observations were performed by the authors or fully qualified radiographers. In most cases two observers were present and served to verify the observation of thumb-sucking. In the main analysis reported below each fetus contributed a single data point. For the 20 fetuses observed three times only the first observation is used in this analysis. Thus the 274 observations reported represent 274 different fetuses. For 50 fetuses at 32-38 weeks of gestational age their position right (either right occiput anterior or transverse) or left (either left occiput anterior or transverse) in the womb was noted as well as the thumb being sucked. Observations on neonates are reported for individuals delivered at 3841 weeks. All were fully developed with Apgar scores of greater than 7. Newborn head position preferences were determined 24 days after birth. All infants were awake at the time of testing and not crying. Individuals were tested in their own cots whilst lying on their backs. The infant’s head was held in the midline position until no pressure was felt on the examiner’s hand and then let go. The side to which the infant turned its head was noted by the examiner. An infant was classified as having turned its head to either right or left when its head position deviated 30 degrees or more from the midline. All infants turned their head well within the allotted IO-min observation period. Care was taken to ensure that there were no lateral sources of stimulation which could influence the turning preference.
RESULTS Fetal thumb-sucking In 274 separate pregnancies, fetuses were observed sucking their thumb (see Table 1). Binomial tests [21] revealed a clear bias for sucking the thumb of the right hand, in total (z=13.834, P
