Objective To assess whether in screening for trisomy 21 by nuchal translucency (NT) the delta or the multiples of the median (MoM)

Background In a previous study we examined the changes in the median multiple of the median (MoM) with gestation of free beta human chorionic gonadotrophin (FbhCG), total human chorionic gonadotrophin (ThCG), a-fetoprotein (AFP) and pregnancy-associated plasma protein A (PAPP-A) in a large series of Down's syndrome pregnancies. Results showed that there was a significant temporal variation of the MoM for each marker. In this paper, we assess the impact of this temporal shift on the estimation of patient-specific risks and the detection rates (DRs) for Down's syndrome pregnancies.

There is significant temporal variation in mean log10MoM values for the screening markers investigated. Screening algorithms, modified to take account of this variation, should allow more accurate gestation-specific risks to be calculated in individual pregnancies.

The distribution of blood spot TSH data from neonates in Wales has revealed no evidence to support the hypothesis that the population is iodine deficient. However, given that mild iodine deficiency has been reported in a cohort that will be childbearing in the next decade, we recommend that the distribution of neonatal blood spot TSH concentrations is monitored by the UK newborn screening programmes to identify any emerging trends in iodine status. Further studies to correlate maternal urinary iodine and newborn blood spot TSH are required to clarify the TSH cut-off points associated with mild iodine deficiency relevant to the time of blood spot sampling in the UK.