REPEAT TESTING OF MOTHERS WITH HIGH HUMAN CHORIONIC-GONADOTROPIN LEVELS IN DOWNS-SYNDROME SCREENING

Multiples of medians of serum markers are assumed to be independent of gestational age: every algorithm used for Down's syndrome risk evalua tion is based on this hypothesis. However, our former observations sug gested that multiples of medians of human chorionic gonadotrophin in D own's syndrome are dependent on gestational age. Furthermore, observat ions on 84 Down's syndrome cases confirmed that human chorionic gonado trophin multiples of medians in samples drawn at 15-17 weeks are appro ximately 10% lower than in samples drawn at 18-21 weeks, thus showing that the human chorionic gonadotrophin concentration decreases about 1 0% less than expected. The control group comprised 554 women with two blood samples and normal human chorionic gonadotrophin at first sampli ng. A further group of 532 women with multiples of medians at first sa mpling > 1.8 was examined with the aim of excluding an association bet ween the human chorionic gonadotrophin trend in Down's syndrome and hi gh starting values. The trend is peculiar to human chorionic gonadotro phin in Down's syndrome pregnancies and may help to explain the increa se in detection rate with gestational age. Based on these findings, sc reening can be optimized, thus improving performance.