Background

• Down Syndrome (Trisomy 21) is the most common chromosomal abnormality, with a frequency of 1:1000 livebirths.¹
• It is commonly diagnosed in the immediate newborn period after an apparently uneventful pregnancy.
• Whilst it is common to offer antenatal screening for Down Syndrome, not all women choose to undergo testing.
  • Non-invasive screening methods (such as serum screening, nuchal skinfold thickness, and ultrasound) have a false-positive and false-negative rate when compared to direct karyotypic testing of fetal genetic material by amniocentesis or chorionic villous sampling.
• Despite the prevalence of structural abnormalities in Trisomy 21, many infants with undiagnosed Trisomy 21 have had fetal anatomy screens performed that have not identified any abnormality.
• Although there is a clear relationship between advancing maternal age and the risk of Trisomy 21, 70% of Down Syndrome infants are born to mothers below the age of 35 years.²
• The risk of Trisomy 21 in the general population primarily depends on maternal age. Approximate risks are:

  15-29 years	1:1500
  30-34 years	1:800
  35-39 years	1:270
  40-44 years	1:100
  >44 years	1:50

• Approximately 94% of Down Syndrome cases will have “classic” Trisomy 21 with a complete copy of an additional chromosome 21.
• The remaining 6% will have mosaicism or an unbalanced translocation (usually between chromosomes 14 and 21).

Assessment in the Neonatal Period

• Diagnosis in the newborn period is a very challenging time for parents and for staff. Often the celebration of the birth of the baby is dampened by the realisation that the infant has a major chromosomal abnormality with significant developmental and health implications.
• The parental response is often one of distress, with a period of anger and/or grief before there is acceptance of the diagnosis.
• All infants - whether diagnosed antenatally or postnatally - should be seen by a neonatal specialist.
• Discussion with the parents should be held in a private place with both parents present.
  • The parents should be given the time they need to absorb the news. Repeat visits may be necessary to deal with questions and distress.
• Information pamphlets and other reading material are available from the Family Liaison Nurse in NICU.
• Routine assessment by the genetics service is not required unless there is doubt about the clinical diagnosis or there are other unusual features.
  • Referral to genetic service is recommended for discussion of recurrence risk, particularly if the trisomy is due to a chromosome translocation or if other chromosomal abnormalities are found on karyotype examination.

Investigations

 Referrals

• Parents should be aware of which referrals have been made.

Referral to paediatrician

Visiting neurodevelopmental therapist

• Note that this is different to the developmental paediatric service. A separate referral (available via the intranet only) needs to be sent.

Social worker

• Can provide parents with appropriate forms for the Child Disability Allowance and other community based support services.
• Will be able to assist with counselling and other support.

Speech language therapy or lactation consultant, as appropriate.

• Infants with Down Syndrome often feed poorly initially and this is frequently the process that determines when the baby will be ready to be discharged.

Audiology (out-patient)

• Hearing impairment occurs in up to 75% of individuals.
• A referral should be sent for audiology assessment.

Ophthalmology clinic, Green Lane Clinical Centre.

• Cataracts, strabismus, and refractory errors are common.  Refer to the ophthalmology service at Green Lane Clinical Centre.

General practitioner

• The GP should be informed that the baby has Down Syndrome, whether significant congenital cardiac disease or other conditions are present, and what follow-up is planned.

Support for Parents

• Information is available from the Nurse Specialist - Family Liason in NICU.
• Provision of the specific Down Syndrome information pack should be withheld until either
  • The karyotype is confirmed, or
  • The parents request the information themselves, or
  • The paediatrician looking after the baby feels that it would be appropriate.
• Parents should be given information about the supports and services the New Zealand Down Syndrome Association (http://nzdsa.org.nz/) can provide to parents and individuals with Down Syndrome.
  • Phone 0800 NZDSAI (0800 693724)
  • Email: national.coordinator@nzdsa.org.nz

Other issues

Genetic Counselling

• It may be appropriate to discuss recurrence risk in the newborn period.
  • For mothers who have had an infant with “classic” Down Syndrome, the generally quoted recurrence risk is 1% (but is higher if maternal age is greater than 40). The recurrence risk for mosaic Down Syndrome is 1-2%.
  • For an unbalanced translocation, then recurrence risk will depend on whether one of the parents has a balanced translocation. The recurrence risk if the mother is a carrier is 12%, and 1% if the father is a carrier.

Other Neonatal Health Issues

• Other structural abnormalities that may present in the perinatal period include duodenal atresia, oesophageal atresia, tracheal stenosis, pyloric stenosis, anorectal anomalies, and Hirshsprung's Disease.
• Persistent pulmonary hypertension is more common in the newborn period, even in the absence of congenital cardiac disease.
• Prophylaxis for bacterial endocarditis will depend on underlying cardiac conditions.
• Airway obstruction is rare in the newborn period but may develop in early childhood.
• Atlanto-axial instability, which occurs in up to 20% of individuals with Down Syndrome, is not usually a significant issue in the newborn period.

References