Average birth weight and length is slightly reduced in CF compared to unaffected infants. In unscreened infants growth rate (weight and length) is reduced in the first year of life, mainly because of impaired nutrition. Once the diagnosis is made and nutrition is improved, catch up growth usually occurs. Individuals diagnosed after newborn screening are taller in childhood than unscreened children picked up later on clinical grounds.
Improvement in the treatment of CF over time has resulted in the patterns of growth in childhood moving nearer to that of unaffected children. There still appears to be a small height deficient in childhood related to CF. Height velocity in childhood is within normal limits. The height deficit can increase further in adolescence because of delay in puberty and in some cases, worsening clinical status. Adult height is usually within the normal range for the population but reduced compared to mid-parental height.
Pituitary function (growth hormone (GH), gonadotrophins, & ACTH) is normal in CF. Chronic infection, nutritional factors and steroid treatment result in GH resistance and can also reduce GH secretion.
Movement across height and weight centiles (up or down) is common in the first 2 years of life and does not necessarily represent a problem. Our data show nutritional status should be normal by 1 year. Most children will settle onto a height centile by 2-3 years of age and after this a child who is growing normally will maintain a height velocity sufficient to keep on the same centile, and will carry on growing along this centile until they commence their pubertal growth spurt. A child with late puberty will have a fall in height centile position and also feel relatively shorter compared to their peers, until they start their pubertal growth spurt. 98% of normal girls have started pubertal development (Tanner breast stage 2) by 13.7 years and 98% of boys have started development (testicular volume over 4 mls) by 14.2 years.
Height (measured with a stadiometer) and weight should be recorded at every clinic visit (minimum every 3 months) and plotted on the standard growth centile charts. In children under 1 year, head circumference (OFC) should be plotted. Mid parental height and parental target centiles should be calculated as shown on the growth chart.
Further assessment is required for children who:
- Are falling from their centile position- they have a poor height velocity over a reasonable period of time (6 months to a year)
- Are very short (below 0.4th centile) even if they are growing at a normal height velocity
- Are very short for their mid-parental height.
Look for factors related to CF which may impact on growth.
- Nutrition - intake or malabsorption. Feeding behaviour problems are common in younger children (see section 7.5).
- impaired glucose tolerance or CF related diabetes
Consider checking for non CF related causes:
- Turner syndrome (this is not always associated with clinical features and it is worth checking karyotype if a girl is very short).
Patients can be discussed with Dr Bridges or Dr Alexander at any stage. They are happy to look at growth charts or assess bone ages for patients.
Investigations which can be done before referral
- Thyroid function, coeliac antibodies and karyotype in girls.
- Bone age (x-ray of the non-dominant wrist and hand) is a way of looking at how much growth there is still to come. Bone age is not likely to be helpful in children under 4 years. Assessment of bone age is operator-dependent and results are more likely to be helpful if the score is assessed by someone with experience.
- One off measurements of GH are not helpful. IGF1 and IGFBP3 are helpful in assessing GH activity but do not distinguish between defects of GH secretion (pituitary problems) and GH action (inflammation, infection, steroids).
- For pubertal delay it may be helpful to check LH, FSH and sex steroid levels although these are likely to be low until mid-puberty.
Consider referral to paediatric endocrinology for the following reasons:
- Pubertal delay (see puberty section 8.3).
- Reduced height velocity or short stature, which does not seem to be caused by CF related problems.
- Concerns by family or child about height.
- Assessment may be of value if there is persistent poor growth velocity even if) there are medical factors sufficient to completely explain the situation (nutritional issues, inflammation, reduced lung function, high dose steroids, etc). There may not be any intervention to improve things but an assessment and explanation may help.
GH deficiency is a rare cause of short stature in the general population. It can occur in CF but the prevalence is not increased. GH deficiency should be considered in short children with persistent poor growth velocity where other causes have been ruled out. Diagnosis requires a stimulation test.
There have been a number of studies of the use of GH in CF patients (without GH deficiency) which have demonstrated short term anabolic benefits. The impact of GH on longer term clinical status is not known, and there is no evidence that GH given in this situation increases adult height. GH is not licenced for use in CF without GH deficiency.