Need for developing case definitions and guidelines for data collection, analysis, and presentation for failure to thrive as an adverse event following maternal immunisation:
Failure to thrive (FTT) is a descriptive term for insufficient growth, usually identified in infancy. Definitions of FTT typically incorporate both clinical characteristics of insufficient growth and specific anthropometric criteria which define it.
Literature related to defining FTT can be broadly categorized in terms of anthropometric indices, aetiological causes, and a variety of variably interchangeable descriptors used to describe FTT or relevant clinical terms. There is no agreed definition and utilisation studies of existing definitions have largely been limited by small sample sizes, apart from two European infant cohorts. These studies agreed that all current means of diagnosing FTT either over or under diagnose the condition and a more accurate diagnostic tool could be beneficial [1], [2]. This paper focuses upon FTT in the first year of life, to assist the investigation of any potential concerns regarding reduced growth in infancy following antenatal maternal immunisation.
Key anthropometric terms include child growth, growth assessment, growth chart monitoring, growth monitoring, and nutritional status. Aetiological literature attempting to define FTT includes the areas of malnutrition and feeding disorders. Relevant clinical descriptors include child health, failure to thrive, growth interruption, growth retardation, weight/growth faltering, malnutrition, wasting, stunting and feeding disorder.
FTT is used as a diagnosis, or a description of a weight gain pattern.
Anthropometric indices have been used universally for defining FTT, yet there is heterogeneity regarding the specific indices, for example weight for age versus weight for height/length. Under-nutrition or inadequate nutrition is thought to be the underlying factor with the consequence of significant interruption to the expected rate of growth, and is strongly linked to malnutrition. In low income countries, malnutrition manifesting as failure to thrive is more common [3], [4], [5], [6], [7], [2].
Normal growth is described in reference to what is regarded as abnormal growth, falling below a pre-determined centile, usually the 3rd. This gives no direct estimate of growth, only of attained weight and clinically children may deviate from their earlier centile position. The growth curve of a normally growing child will represent gradual and incremental increases in weight from birth and is based on regular weight recordings [8], [9].
Among infants, determining FTT presents its own set of challenges. For example, in infants and young children with genetic short stature, prematurity, or intrauterine growth restriction who have an acceptable weight-for-length and normal growth velocity the term FTT is not used [10], [11]. Additionally, the well-recognized phenomenon of some healthy infants born above expected weight to experience an initial fall below birth centiles over the first 6–12 months, before following their “correct” centile, also known as ‘regression to the mean’, further complicates the specificity of FTT definitions based upon growth trajectory [12], [13]. This phenomenon has also been termed “catch down” growth [14].
