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Very low birth weight newborns do not need repeat screening for congenital hypothyroidism. Vincent MA, Rodd C, Dussault JH, et al. J Pediatr (March 2002);140:311-4. .
The study objective was to determine whether repeat screening for congenital hypothyroidism is necessary in very low birth weight (VLBW, <1500 gm) infants. All VLBW infants born in the province of Québec between October 15, 1993, and October 15, 1994, had a second filter paper sample requested at 6 weeks of age to measure thyrotropin and thyroxine. We then conducted a survey of all 4 academic pediatric endocrinology clinics in the province, inquiring about cases of permanent primary congenital hypothyroidism (PPCH) in children born weighing <1500 g or who may have been missed by neonatal screening.

Results: Two specimens were obtained in 465 VLBW newborns. One case of mild transient hyperthyrotropinemia was identified. The survey identified 4 VLBW newborns with PPCH: 1 girl and 1 boy with dyshormonogenesis, 1 athyreotic girl, and 1 girl with thyroid ectopy. All 4 were detected by their initial filter paper specimens. The survey also identified 1 case of PPCH in a girl who had a normal neonatal screen and normal birth weight.

Comment. At issue in this study is the management of VLBW premature babies that are suspected of having "hypothyroxinemia of prematurity" (low T4 with normal TSH) in their initial thyroid screens. Previous reviews have found instances of VLBW infants who had normal TSH values initially, and elevated TSH on repeat screening at 2 – 8 weeks of age. Mandel et al (Thyroid 2000; 10:693-5) described 10 such cases of "atypical hypothyroidism" in a sample of thyroid tests on 3238 VLBW newborns, but did not document the final diagnoses on these babies. In the present study, only 1 case of delayed hyperthyrotropinemia was identified out of 465 VLBW newborns, and that patient had a normal TSH on follow up testing 13 days later. Based on this, the authors concluded that repeat thyroid testing on VLBW newborns is unnecessary. In light of the serious consequences of an untreated case of PPCH, I doubt that the sample size of this study is adequate to justify this recommendation. ABK

Additional Comments:

Date:  10/21/2005
Time 12:21

In the UK screening fraternity there is some debate currently as to whether
only LBW/VLBWs may be 'missed' for PPCH or whether this applies to newborns
of all gestations, the latter being many people's view here and also (rare)
experience.  Babies are not routinely screened a second time in the UK.

My reason for writing is that I'd like to take this enquiry/discussion
further than is possible in my tiny country.

Kindest regards

Kate

Ms Kate Hall
Principal Biochemist and Section Head
West Midlands Newborn Screening Programme
Birmingham Children's Hospital
Steelhouse Lane
B4 6NH
Tel:    (+44) 0121 333 9903
Fax:    (+44) 0121 333 9911
Email:    kate.hall@bch.nhs.uk 

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