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Aims: To evaluate the cross-trimester multiple marker correlation and the minimum marker combination needed for detecting various chromosomal aneuploidies. Materials and methods: Parturient women with singleton pregnancies who underwent non-interventional sequential screening test and followed prospectively were recruited. They all underwent first trimester combined nuchal translucency (NT), pregnancy-associated plasma protein-A (PAPP-A), and free β-human chorionic gonadotrophin (f-βhCG), followed by second trimester measurement of unconjugated estriol (uE 3 ), human chorionic gonadotrophin (hCG) and alpha-fetoprotein (AFP). Pearson correlation was applied to compute any cross-trimester marker correlation and logistic regression analysis was used to determine the minimum marker combination for detecting various categories of chromosomal aneuploidies. Results: The current study included 552 normal and 43 chromosomal-affected pregnancies (24 Down's syndrome [DS], 7 Turner's syndrome, 8 Edward's syndrome, 4 Klinefelter syndrome and 5 triploidy) for which the results of both the screening tests and the pregnancy outcome were available. In the normal cases, a significant correlation was found between f-βhCG and hCG (r=0.52), as well as between PAPP-A and uE 3 (r=0.174). In DS pregnancies, the NT correlated with both hCG (r=0.45) and uE 3 (r= -0.39). In Turner's syndrome, uE 3 correlated both with PAPP-A (r=0.97) and f-βhCG (r=0.97). No other significant correlations were found. Furthermore, with the exception of f-βhCG and hCG in the unaffected cases, all other markers correlation appeared very weak. For detecting all the above categories of aneuploidies, the combination of NT, PAPP-A and uE 3 and the maternal age background risk were found adequate, with a 74% detection rate (DR) for a 5% false positive rate (FPR). For DS only, the combination of maternal age-related background risk and the combination of NT, PAPP-A, hCG and AFP yielded a 79% DR for a 5% FPR. Conclusions: The current study agrees with a previous report that, overall, there is no strong correlation between first and second trimester markers. The extension of the integrated test for detecting various categories of common chromosomal aneuploidies using NT, PAPP-A and uE 3 deserves further evaluation.