[Normal thyroid-stimulating hormone levels in screening for congenital hypothyroidism in newborn twins]

A large number of articles have been published since neonatal screening for congenital hypothyroidism (CH) started in the 1970s. Surprisingly, little information on false negative results in these screenings has been reported.

Thyroid-stimulating hormone (THS) levels were determined in 360,651 newborn infants in Malaga until March 2005. One hundred and fifty-six CH cases were detected, of which 86 % were permanent and 14 % were transient. In this study, we retrospectively analyzed a group of 13 CH dizygotic twins in which only one of the twins had CH.

The first two patients were diagnosed late and data on whether they were included in neonatal screening were lacking. In seven of the 13 patients, TSH values were initially normal: five patients were diagnosed by a second test performed 14 days after birth and were treated before they were 1 month old, and two were diagnosed and treated late because a second test was not performed. In the remaining four patients, TSH values were initially elevated but were lower than confirmation test values.

It is now widely accepted that thyroid function could be compensated between two dizygotic twins if only one of the twins has CH, leading to a false negative result. The results of the present study indicate the need to repeat the test for CH 14 days after birth in all dizygotic twins.