1. Snijders RJM, Nicolaides KH. Ultrasound Markers for Fetal Chromosomal Defects. New York: Parthenon Publishing Group, 1995.

2. Vintzileos AM, Campbell WA, Rodis JF, Guzman ER, Smulian JC, Knuppel RA. The use of second-trimes­ter genetic sonogram in guiding clinical management of patients at increased risk for fetal trisomy 21. Obstet Gynecol 1996; 87(6): 948-952.

3. Egan JF, Benn P, Borgida AF, Rodis JF, Campbell WA, Vintzileos AM. Efficacy of screening for fetal Down syndrome in the United States from 1974 to 1997. Obstet Gynecol 2000; 96(6): 979-985.

4. Haddow JE, Palomaki GE, Knight GJ, Cunningham GC, Lustig LS, Boyd PA. Reducing the need for amnio­centesis in women 35 years of age or older with serum markers for screening. N Engl J Med 1994; 330(16): 1114-1118.

5. Vintzileos AM, Guzman ER, Smulian JC, McLean DA, Ananth CV. Choice of second-trimester genetic sono­gram for detection of trisomy 21. Obstet Gynecol 1997; 90(2): 187-190.

6. Bahado-Singh R, Deren O, Oz U, Tan A, Hunter D, Copel J, Mahoney MJ. An alternative for women initially declining genetic amniocentesis: individual Down syn­drome odds on the basis of maternal age and multiple ultrasonographic markers. Am J Obstet Gynecol 1998; 179(2): 514-519.

7. Benacerraf BR, Frigoletto FD Jr, Laboda LA. Sonographic diagnosis of Down syndrome in the second trimester. Am J Obstet Gynecol 1985; 153(1) :49-52.

8. Benacerraf BR, Neuberg D, Bromley B, Frigoletto FD Jr. Sonographic scoring index for prenatal detection of chromosomal abnormalities. J Ultrasound Med 1992; 11(9): 449-458.

9. Nadel AS, Bromley B, Frigoletto FD Jr, Benacerraf BR. Can the presumed risk of autosomal trisomy be de­creased in fetuses of older women following a normal sonogram? J Ultrasound Med 1995; 14(4): 297-302.

10. Nyberg DA, Luthy DA, Cheng EY, Sheley RC, Resta RG, Williams MA. Role of prenatal ultrasonog­raphy in women with positive screen for Down syndrome on the basis of maternal serum markers. Am J Obstet Gynecol 1995; 173(4): 1030-1035.

11. Vintzileos AM, Egan JF. Adjusting the risk for trisomy 21 on the basis of second-trimester ultrasonog­raphy. Am J Obstet Gynecol 1995; 172(3): 837-844.

12. Shipp TD, Benacerraf BR. Second trimester ultra­sound screening for chromosomal abnormalities. Prenat Diagn 2002; 22(4): 296-307.

13. Benacerraf BR, Miller WA, Frigoletto FD Jr. Sonographic detection of fetuses with trisomies 13 and 18: accuracy and limitations. Am J Obstet Gynecol 1988; 158(2): 404-409

14. Benacerraf BR, Harlow B, Frigoletto FD Jr. Are choroid plexus cysts an indication for second-trimester amniocentesis? Am J Obstet Gynecol 1990; 162(4): 1001-1006.

15. Nyberg DA, Kramer D, Resta RG, Kapur R, Mahony BS, Luthy DA, Hickok D. Prenatal sonographic findings of trisomy 18: review of 47 cases. J Ultrasound Med 1993; 12(2): 103-113.

16. Lehman CD, Nyberg DA, Winter TC 3rd, Kapur RP, Resta RG, Luthy DA. Trisomy 13 syndrome: prenatal US findings in a review of 33 cases. Radiology 1995; 194(1): 217-222.

17. Roberts DJ, Genest D. Cardiac histologic pathol­ogy characteristic of trisomies 13 and 21. Hum Pathol. 1992; 23(10): 1130-1140.

18. Jauniaux E, Brown R, Rodeck C, Nicolaides KH. Prenatal diagnosis of triploidy during the second trimester of pregnancy. Obstet Gynecol 1996; 88(6): 983-989.

19. Benacerraf BR, Frigoletto FD Jr. Soft tissue nuchal fold in the second-trimester fetus: standards for normal measurements compared with those in Down syn­drome. Am J Obstet Gynecol 1987; 157(5): 1146-1149.

20. Benacerraf BR, Frigoletto FD Jr, Cramer DW. Down syndrome: sonographic sign for diagnosis in the second-trimester fetus. Radiology 1987; 163(3): 811-813.

21. Crane JP, Gray DL. Sonographically measured nuchal skinfold thickness as a screening tool for Down syndrome: results of a prospective clinical trial. Obstet Gynecol 1991; 77(4): 533-536.

22. Watson WJ, Miller RC, Menard MK, Chescheir NC, Katz VL, Hansen WF, Wolf EJ. Ultrasonographic measurement of fetal nuchal skin to screen for chromo­somal abnormalities. Am J Obstet Gynecol 1994; 170(2): 583-586.

23. Borrell A, Costa D, Martinez JM, Delgado RD, Casals E, Ojuel J, Fortuny A. Early midtrimester fetal nuchal thickness: effectiveness as a marker of Down syn­drome. Am J Obstet Gynecol 1996; 175(1): 45-49.

24. Bahado-Singh RO, Goldstein I, Uerpairojkit B, Copel JA, Mahoney MJ, Baumgarten A. Normal nuchal thickness in the midtrimester indicates reduced risk of Down syndrome in pregnancies with abnormal triple-screen results. Am J Obstet Gynecol 1995; 173(4): 1106-1110.

25. Nicolaides KH, Heath V, Cicero S. Increased fetal nuchal translucency at 11-14 weeks. Prenat Diagn 2002; 22(4): 308-315.

26. Fakhry J, Reiser M, Shapiro LR, Schechter A, Pait LP, Glennon A. Increased echogenicity in the lower fetal abdomen: a common normal variant in the second trimester. J Ultrasound Med 1986; 5(9): 489-492.

27. Scioscia AL, Pretorius DH, Budorick NE, Cahill TC, Axelrod FT, Leopold GR. Second-trimester echo­genic bowel and chromosomal abnormalities. Am J Obstet Gynecol 1992; 167(4 Pt 1): 889-894.

28. Hogge WA, Hogge JS, Boehm CD, Sanders RC. Increased echogenicity in the fetal abdomen: use of DNA analysis to establish a diagnosis of cystic fibrosis. J Ultra­sound Med 1993; 12(8): 451-454.

29. Nyberg DA, Resta RG, Mahony BS, Dubinsky T, Luthy DA, Hickok DE, Luthardt FW. Fetal hyperecho­genic bowel and Down's syndrome. Ultrasound Obstet Gynecol 1993; 3(5): 330-333.

30. Bahado-Singh R, Morotti R, Copel JA, Mahoney MJ. Hyperechoic fetal bowel: the perinatal consequences. Prenat Diagn 1994; 14(10): 981-987.

31. Bromley B, Doubilet P, Frigoletto FD Jr, Krauss C, Estroff JA, Benacerraf BR. Is fetal hyperechoic bowel on second-trimester sonogram an indication for amniocen­tesis? Obstet Gynecol 1994; 83(5 Pt 1): 647-651.

32. Hill LM, Fries J, Hecker J, Grzybek P. Second-trimester echogenic small bowel: an increased risk for adverse perinatal outcome. Prenat Diagn 1994; 14(9): 845-850.

33. Nyberg DA, Luthy DA, Resta RG, Nyberg BC, Williams MA. Age-adjusted ultrasound risk assessment for fetal Down’s syndrome during the second trimester: de­scription of the method and analysis of 142 cases. Ultra­sound Obstet Gynecol 1998; 12(1): 8-14.

34. Lockwood C, Benacerraf B, Krinsky A, Blake­more K, Belanger K, Mahoney M, Hobbins J. A sono­graphic screening method for Down syndrome. Am J Obstet Gynecol 1987; 157(4 Pt 1): 803-808.

35. FitzSimmons J, Droste S, Shepard TH, Pascoe-Mason J, Chinn A, Mack LA. Long-bone growth in fetuses with Down syndrome. Am J Obstet Gynecol 1989; 161(5): 1174-1177.

36. Benacerraf BR, Neuberg D, Frigoletto FD Jr. Humeral shortening in second-trimester fetuses with Down syndrome. Obstet Gynecol 1991; 77(2): 223-227.

37. Ginsberg N, Cadkin A, Pergament E, Verlinsky Y. Ultrasonographic detection of the second-trimester fetus with trisomy 18 and trisomy 21. Am J Obstet Gynecol 1990; 163(4 Pt 1): 1186-1190.

38. Biagiotti R, Periti E, Cariati E. Humerus and femur length in fetuses with Down syndrome. Prenat Diagn 1994; 14(6): 429-434.

39. Johnson MP, Michaelson JE, Barr M Jr, Tread­well MC, Hume RF Jr, Dombrowski MP, Evans MI. Com­bining humerus and femur length for improved ultrasono­graphic identification of pregnancies at increased risk for trisomy 21. Am J Obstet Gynecol 1995; 172(4 Pt 1): 1229-1235.

40. Nyberg DA, Resta RG, Luthy DA, Hickok DE, Williams MA. Humerus and femur length shortening in the detection of Down's syndrome. Am J Obstet Gynecol. 1993; 168(2): 534-538.

41. Rodis JF, Vintzileos AM, Fleming AD, Ciarleglio L, Nardi DA, Feeney L, Scorza WE, Campbell WA, Ingardia C. Comparison of humerus length with femur length in fetuses with Down syndrome. Am J Obstet Gyne­col 1991; 165(4 Pt 1): 1051-1056.

42. LaFollette L, Filly RA, Anderson R, Golbus MS. Fetal femur length to detect trisomy 21. A reappraisal. J Ultrasound Med 1989; 8(12): 657-660.

43. Hadlock FP, Harrist RB, Martinez-Poyer J. Fetal body ratios in second trimester: a useful tool for identify­ing chromosomal abnormalities? J Ultrasound Med 1992; 11(2): 81-85.

44. Grandjean H, Sarramon MF. Femur/foot length ratio for detection of Down syndrome: results of a multi­center prospective study. The Association Francaise pour le Depistage et la Prevention des Handicaps de l'Enfant Study Group. Am J Obstet Gynecol. 1995; 173(1): 16-19.

45. Shipp TD, Bromley B, Mascola M, Benacerraf B. Variation in fetal femur length with respect to maternal race. J Ultrasound Med 2001; 20(2): 141-144.

46. Vintzileos AM, Egan JF, Smulian JC, Campbell WA, Guzman ER, Rodis JF. Adjusting the risk for trisomy 21 by a simple ultrasound method using fetal long-bone biometry. Obstet Gynecol 1996; 87(6): 953-958.

47. Brown DL, Roberts DJ, Miller WA. Left ventricu­lar echogenic focus in the fetal heart: pathologic correla­tion. J Ultrasound Med 1994; 13(8): 613-616.

48. Shipp TD, Bromley B, Lieberman E, Benacerraf BR. The frequency of the detection of fetal echogenic intracardiac foci with respect to maternal race. Ultrasound Obstet Gynecol 2000; 15(6): 460-462.

49. Bromley B, Lieberman E, Laboda L, Benacerraf BR. Echogenic intracardiac focus: a sonographic sign for fetal Down syndrome. Obstet Gynecol 1995; 86(6): 998-1001.

50. Schechter AG, Fakhry J, Shapiro LR, Gewitz MH. In utero thickening of the chordae tendinae. A cause of intracardiac echogenic foci. J Ultrasound Med 1987; 6(12): 691-695.

51. Levy DW, Mintz MC. The left ventricular echo­genic focus: a normal finding. AJR Am J Roentgenol 1988; 150(1): 85-86.

52. Bromley B, Lieberman E, Shipp TD, Richardson M, Benacerraf BR. Significance of an echogenic intra­cardiac focus in fetuses at high and low risk for aneu­ploidy. J Ultrasound Med 1998; 17(2): 127-131.

53. Sepulveda W, Romero D. Significance of echo­genic foci in the fetal heart. Ultrasound Obstet Gynecol 1998; 12(6): 445-449.

54. Wax JR, Philput C. Fetal intracardiac echogenic foci: does it matter which ventricle? J Ultrasound Med 1998; 17(3): 141-144; quiz 145-146.

55. Yoder PR, Sabbagha RE, Gross SJ, Zelop CM. The second-trimester fetus with isolated choroid plexus cysts: a meta-analysis of risk of trisomies 18 and 21. Obstet Gynecol 1999; 93(5 Pt 2): 869-872.

56. Bromley B, Lieberman R, Benacerraf BR. Choroid plexus cysts: not associated with Down syndrome. Ultrasound Obstet Gynecol 1996; 8(4): 232-235.

57. Gross SJ, Shulman LP, Tolley EA, Emerson DS, Felker RE, Simpson JL, Elias S. Isolated fetal choroid plexus cysts and trisomy 18: a review and meta-analysis. Am J Obstet Gynecol 1995; 172(1 Pt 1): 83-87.

58. Benacerraf BR, Mandell J, Estroff JA, Harlow BL, Frigoletto FD Jr. Fetal pyelectasis: a possible associa­tion with Down syndrome. Obstet Gynecol 1990; 76(1): 58-60.

59. Corteville JE, Dicke JM, Crane JP. Fetal pyelect­asis and Down syndrome: is genetic amniocentesis war­ranted? Obstet Gynecol 1992; 79(5): 770-772.

60. Thompson MO, Thilaganathan B. Effect of routine screening for Down’s syndrome on the significance of isolated fetal hydronephrosis. Br J Obstet Gynaecol 1998; 105(8): 860-864.

61. Bork MD, Egan JF, Cusick W, Borgida AF, Campbell WA, Rodis JF. Iliac wing angle as a marker for trisomy 21 in the second trimester. Obstet Gynecol 1997; 89(5 Pt 1): 734-737.

62. Shipp TD, Bromley B, Lieberman E, Benacerraf BR. The iliac angle as a sonographic marker for Down syndrome in second-trimester fetuses. Obstet Gynecol 1997; 89(3): 446-450.

63. Freeman SB, Taft LF, Dooley KJ, Allran K, Sher­man SL, Hassold TJ, Khoury MJ, Saker DM. Population-based study of congenital heart defects in Down syn­drome. Am J Med Genet 1998; 80(3): 213-217.

64. Vintzileos AM, Guzman ER, Smulian JC, Yeo L, Scorza WE, Knuppel RA. Second-trimester genetic sonog­raphy in patients with advanced maternal age and normal triple screen. Obstet Gynecol 2002; 99(6): 993-995.

65. Benacerraf BR, Osathanondh R, Frigoletto FD. Sonographic demonstration of hypoplasia of the middle phalanx of the fifth digit: a finding associated with Down syndrome. Am J Obstet Gynecol 1988; 159(1): 181-183.

66. Birnholz JC, Farrell EE. Fetal ear length. Pediat­rics 1988; 81(4): 555-558.

67. Lettieri L, Rodis JF, Vintzileos AM, Feeney L, Ciarleglio L, Craffey A. Ear length in second-trimester aneuploid fetuses. Obstet Gynecol 1993; 81(1): 57-60.

68. Bahado-Singh RO, Wyse L, Dorr MA, Copel JA, O'Connor T, Hobbins JC. Fetuses with Down syndrome have disproportionately shortened frontal lobe dimensions on ultrasonographic examination. Am J Obstet Gynecol 1992; 167(4 Pt 1): 1009-1014.

69. Rotmensch S, Goldstein I, Liberati M, Shalev J, Ben-Rafael Z, Copel JA. Fetal transcerebellar diameter in Down syndrome. Obstet Gynecol 1997; 89(4): 534-537.

70. Wilkins I. Separation of the great toe in fetuses with Down syndrome. J Ultrasound Med 1994; 13(3): 229-231

71. Bromley B, Shipp TD, Benacerraf BR. Amnion-chorion separation after 17 weeks’ gestation. Obstet Gyne­col 1999; 94(6): 1024-1026.

72. Vintzileos AM, Guzman ER, Smulian JC, Day-Salvatore DL, Knuppel RA. Indication-specific accuracy of second-trimester genetic ultrasonography for the detec­tion of trisomy 21. Am J Obstet Gynecol 1999; 181(5 Pt 1): 1045-1048.

73. Bahado-Singh RO, Deren O, Tan A, D'Ancona RL, Hunter D, Copel JA, Mahoney MJ. Ultrasono­graphically adjusted midtrimester risk of trisomy 21 and significant chromosomal defects in advanced maternal age. Am J Obstet Gynecol 1996; 175(6): 1563-1568.

74. DeVore GR, Romero R. Combined use of genetic sonography and maternal serum triple-marker screening: an effective method for increasing the detection of trisomy 21 in women younger than 35 years. J Ultrasound Med 2001; 20(6): 645-654.

75. Vintzileos AM, Campbell WA, Guzman ER, Smulian JC, McLean DA, Ananth CV. Second-trimester ultrasound markers for detection of trisomy 21: which markers are best? Obstet Gynecol 1997; 89(6): 941-944.

76. Benacerraf BR, Nadel A, Bromley B. Identifica­tion of second-trimester fetuses with autosomal trisomy by use of a sonographic scoring index. Radiology 1994; 193(1): 135-140.

77. Bromley B, Shipp T, Benacerraf BR. Genetic sonogram scoring index: accuracy and clinical utility. J Ultrasound Med 1999; 18(8): 523-528; quiz 529-530.

78. Bahado-Singh RO, Tan A, Deren O, Hunter D, Copel J, Mahoney MJ. Risk of Down syndrome and any clinically significant chromosome defect in pregnancies with abnormal triple-screen and normal targeted ultrasono­graphic results. Am J Obstet Gynecol 1996; 175(4 Pt 1): 824-829.

79. Verdin SM, Economides DL. The role of ultra­sonographic markers for trisomy 21 in women with posi­tive serum biochemistry. Br J Obstet Gynaecol 1998; 105(1): 63-67.