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Prevailing head position to one side in early infancy—A population‐based study

Abstract Aim To determine the prevalence of prevailing head position to one side (PHP) in young infants and to evaluate its associations with reaching performance, neurological condition and perinatal and socio‐economic factors. Methods Observational study in 500 infants (273 boys) 2‐6 months corrected age, representative of the Dutch population (median gestational age 39.7 weeks (27‐42); birthweight 3438 g (1120‐4950). Prevailing head position to one side and reaching performance were assessed with the Infant Motor Profile; neurological condition with the Standardized Infant NeuroDevelopmental Assessment. Socio‐economic information and perinatal information were obtained by questionnaire and medical records. Associations were analysed with uni‐ and multivariable statistics. Results Prevailing head position to one side was observed in 100 infants (20%), and its prevalence decreased from 49% at 2 months to 0% at 6 months. Only in infants aged 4‐5 months PHP was significantly associated with worse reaching and an at‐risk neurological score. Prevailing head position to one side was weakly associated with prenatal substance exposure, post‐natal admission to a paediatric ward and paternal native Dutch background. Conclusion Prevailing head position to one side at 2‐3 months is a frequently occurring sign with limited clinical significance. Yet, PHP at 4‐5 months is associated with a worse functional and neurological condition. Therefore, PHP at 4‐5 months could serve as a red flag indicating possible challenges in later development.

contralateral side. This exploratory behaviour allows infants to learn to control their bodies. 2 This, in turn, is essential for the development of early behaviours in which vision and movements of trunk and arms are involved, such as reaching and grasping-behaviours that are largely dependent on adequate postural control. [3][4][5] Impaired head control is regarded as a manifestation of neurological non-optimality. Therefore, items evaluating head behaviour are included in all common infant neurological assessment methods. [6][7][8] A frequently occurring clinical manifestation of non-optimal head control is a prevailing head position to one side (PHP). 9 The prevalence of PHP increased after the launch of the Back to Sleep campaign by the American Academy of Pediatrics in 1994, rising to 10%-11% in infants aged 2-4 months in the Netherlands in 2001. 10,11 PHP may lead to deformational plagiocephaly, a condition that has been associated with developmental delays in gross and fine motor function, problem-solving and personal social skills. [12][13][14] Although the studies reporting these associations have several limitations and only show tentative results, they do state that PHP could be a marker of conditions impeding typical development, such as neuromuscular conditions and environmental positioning limitations. 15 Professional awareness of these associations and caregivers' concerns about the asymmetric motor behaviour of the infant frequently results in referral to paediatric physiotherapy. 10 Knowledge about the current prevalence of PHP in the general population is sparse. The data available are Dutch data of infants aged 2-6 months of the general population in 1995, 10

| Study population
In this cross-sectional study, we evaluated motor behaviour of 500 infants (273 boys and 227 girls) aged 2-6 months corrected age (CA).
The infants were the youngest infants of the IMP-SINDA project.
Inclusion criteria of the IMP-SINDA project were as follows: age 2-18 months CA living in the northern part of the Netherlands (covering about a quarter of the surface area of the Netherlands) and having caregivers with sufficient comprehension of the Dutch language. Infants were only excluded if they were too ill to be assessed (eg severe congenital heart disease with insufficient oxygen saturation). We achieved the aim to recruit 100 infants per age month, whose socio-economic background is representative of the general Dutch population. Recruitment took place at well-baby clinics and by advertisements. Each infant was assessed once. The infant's age in a specific age month category ranged from 2 weeks prior to the exact age in months CA to 2 weeks after that exact age, for example the age of 3 months CA ranged from 2 months and 15 days to 3 months and 14 days. The Medical Ethical Committee of the University Medical Centre Groningen (UMCG) approved the study design (approval number: METc 2016/294). All caregivers provided written informed consent.

| Perinatal and socio-economic characteristics
Caregivers filled out a standardised questionnaire on prenatal, perinatal and neonatal (in short: perinatal) and socio-economic history.

Key notes
• In the general Dutch population, the prevalence of prevailing head position (PHP) steeply decreases from 49% at 2 months to 0% at 6 months.
• PHP at 2-3 months has limited clinical significance, but PHP at 4-5 months is associated with worse functional and neurological condition.
• PHP in the general population is only weakly associated with perinatal risk factors.
If the questionnaire revealed complications, medical records were consulted. Based on these data, a perinatal risk score was calculated (Table 1).

| Infant Motor Profile
Prevailing head position to one side was determined on the basis of the IMP, a valid and reliable video-based assessment of selfproduced motor behaviour in different positions in infants aged 3-18 months. Its 80 items provide information on the domains variation, adaptability, symmetry, fluency and motor performance. 19 The IMP includes three items on PHP, that is items evaluate the presence of asymmetrical head position in supine, prone and (supported) sitting position. These IMP items are scored as no or mildly/ moderately/strongly PHP. Prevailing head position to one side was defined as the presence of a moderately or strongly prevailing head position in at least two of the three positions mentioned above. The infant's ability to reach, grasp and manipulate was based on the IMPperformance item assessing this ability when the infant sits on the caregiver's lap (score range 1-7; a higher score denotes a better performance; Table 2).

| SINDA's neurological scale
The SINDA is a novel neurodevelopmental screening instrument applicable for infants aged 6 weeks to 12 months. SINDA's neurological scale consists of 28 items, scored as typical or atypical. It results in a score ranging from 0 to 28, with 28 indicating best performance.
A total score of ≤ 21 (the at-risk neurological score) was associated with an increased risk of a developmental disorder. 7 One of the items evaluates the infant's behaviour during the pull-to-sit manoeuvre.
Atypical performance implies the presence of head lag, active head retroflection and/or insufficient hip flexion. The first study on SINDA's neurological scale indicated that it is a reliable and valid assessment tool. 7

| Statistical analysis
To calculate the study's power a two-sample t test for the reaching parameter was performed, assuming that the overall prevalence of PHP at 2-6 months was 6%. 10 Considering a 1-point difference in the reaching score as clinically relevant, the sample size of 500 results in a power of 80% (α = .05).
Associations between PHP on the one hand and reaching behaviour and SINDA's total neurological score on the other were evaluated with the Mann-Whitney U test; those between PHP and an at-risk neurological score and atypical pull-to-sit manoeuvre with the chi-square test, with Phi as the measure of the effect size.
Associations between PHP and perinatal risk factors were assessed with the chi-square test and the Mann-Whitney U test. Next, we performed backward multivariable logistic regression analysis to determine which factors contributed most to PHP; only factors that reached P < .15 in the univariable analyses were entered into this analysis. Throughout the analyses, confidence intervals (CI) were set at 95%, and P-values < .05 were considered statistically significant (two-tailed). In case of missing data on perinatal characteristics, cases were omitted from the association analyses. Statistical analyses were performed using Statistical Package for the Social Sciences (SPSS), version 23 (SPSS IC., Chicago, IL).

| RE SULTS
The background characteristics of the study group are shown in Table 1. They reflect the low-risk nature of the group with a median gestational age of 39.7 weeks (range 27-42) and a median birthweight of 3438 g (range 1120-4950). The study group contained two infants with a known syndrome: one was diagnosed with trisomy 21 and one with Gorlin syndrome. The background characteristics resemble those of the general Dutch population, including the prevalence of preterm birth (6.2% in our study and 6.8% in the general population) 20 and the infants' socio-economic background (prevalence of highly educated mothers 40% in our study and 37% in the general population). 21

| Prevalence of PHP
The prevalence of PHP in our total study group was 20%, with a steady and significant decrease from 49% at 2 months to 0% at 6 months (Table 2, Figure 1A).

| PHP and performance on reaching, grasping and manipulation
Prevailing head position to one side was significantly associated with worse reaching, grasping and manipulation (in short: reaching; P < .001; Table 2). This association was age dependent ( Figure 1B): only infants aged 4-5 months with PHP scored significantly lower on reaching than their peers without PHP (P < .001).

| SINDA's neurological scale scores and PHP
SINDA's neurological scores ranged from 11 to 28 points, with a median value of 25. This reflects the low-risk nature of the study group. Prevailing head position to one side was associated with a significantly lower SINDA neurological score; this held true for all ages ( Figure 1C). Fifty-five infants of the total group (11%) had an at-risk neurological score. Also, the at-risk score was associated with PHP (P < .001). The association was age dependent. In the infants aged 2-3 months, the at-risk score was not associated with PHP (at-risk score in infants with PHP: 18/81 (22%); in infants without PHP 16/119 (13%)) (χ 2 (1) = 2.631, Phi = 0.115, P = .105). However, in infants aged 4-5 months the at-risk score was associated with PHP (at-risk score in infants with PHP: 6/19 (32%); in infants without PHP: 10/181 (6%); χ 2 (1) = 15.859, Phi = 0.282, P < .001). An atypical performance on the pull-to-sit manoeuvre was present in 172 infants (34%). It was clearly associated with PHP (χ 2 (1) = 33.318, Phi = 0.258, P < .001). This association was not age dependent.

| Perinatal risk factors and PHP
Univariable analyses revealed that PHP was significantly associated maternal smoking, prenatal substance exposure, maternal medication, diabetes, hypertension, thyroid disease n = 1; meconium in amniotic fluid n = 2; non-optimal start, admission to neonatal ward, jaundice requiring phototherapy n = 1; perinatal risk score n = 34.
The perinatal risk score was not associated with PHP (P = .748).
Multivariable logistic regression analysis indicated that prenatal sub-

| D ISCUSS I ON
In our low-risk study group, 20% of infants showed PHP, with a prevalence that decreased from 49% at 2 months to 0% at 6 months.
Prevailing head position to one side in infants aged 2-3 months was not related to reaching nor to an at-risk neurological score. However, in infants aged 4-5 months PHP was associated with less optimal reaching and an at-risk neurological condition. Perinatal factors were only weakly associated with PHP.
The prevalence of PHP at 4 months in our study (16%) is somewhat higher than the 11% previously reported in a large study group of infants younger than 6 months assessed in 1995 that was relatively representative of the Dutch population. 10  sensory and motor cortices no longer involve the temporary structure of the subplate; from that age onwards, they only rely on the permanent circuitries of the cortical plate. 22 This developmental change is accompanied by a transition in the infant's behaviour: the general movements are in their final phase and are getting replaced by goal-directed behaviour. 23,24 Simultaneously the infant has achieved the ability to balance the head. 25 Proper head balance is one of the prerequisites for goal-directed reaching. 3,5 Interestingly, having a non-native Dutch father was associated with a lower risk of PHP, which supports the suggestion that ethnic background and cultural habits may play a role in the genesis of PHP. 18,26 PHP was only associated with two perinatal risk factors: prenatal substance exposure and post-natal admission to the neonatal ward. The latter suggests that PHP is associated with an impaired capacity to cope with the transition from intra-to extrauterine life, which in turn corresponds to the less optimal neurological condition of infants with PHP ( Figure 1). In contrast to other reports, 10,17 we did not find an association between PHP and preterm birth and male sex. The reason that we did not find an association with preterm birth could be that in our sample, that was representative of the

| CON CLUS ION
We found a 20% overall prevalence of PHP in young infants. Our study confirms that PHP in young infants is largely age dependent. In our  28  27  26  25  24  23  22  21  20  19  18  17  16  15  12  11 PHP no PHP