Combining nuchal translucency and serum markers in prenatal screening for Down syndrome in twin pregnancies

A method is described to combine the ultrasound marker nuchal translucency (NT) with serum markers so that they can be used together in prenatal screening for Down syndrome in twin pregnancies. For monochorionic twin pregnancies (taken as monozygous), the two fetus‐specific NT measurements are averaged before risk is calculated and before the contribution of the serum markers is incorporated. For dichorionic twin pregnancies (taken as dizygous), the risk for each fetus based on the individual NT measurements is calculated, the two fetus‐specific risks are added together, and then the contribution of the serum markers is incorporated. In this way, all the screening markers can be used in combination to produce a pregnancy‐specific ‘pseudo‐risk’, rather than a fetus‐specific pseudo‐risk. We refer to pseudo‐risk because in the absence of sufficient data on the screening markers in affected twin pregnancies, a true risk estimate cannot be calculated. Tentative estimates are given of screening performance in twins using NT, the combined test (NT with first‐trimester serum markers), and the integrated test (NT with first‐ and second‐trimester serum markers), all interpreted with maternal age. Copyright © 2003 John Wiley & Sons, Ltd.

[1]  N. Wald,et al.  Serum screening for Down's syndrome between 8 and 14 weeks of pregnancy , 1996, British journal of obstetrics and gynaecology.

[2]  K. Nicolaides,et al.  Letter. Correct estimation of parameters for ultrasound nuchal translucency screening , 1998, Prenatal diagnosis.

[3]  H. Cuckle,et al.  Estimating a woman's risk of having a pregnancy associated with Down's syndrome using her age and serum alpha‐fetoprotein level , 1987, British journal of obstetrics and gynaecology.

[4]  K. Nicolaides,et al.  Early prediction of severe twin-to-twin transfusion syndrome. , 2000, Human reproduction.

[5]  N. Wald,et al.  Combining Ultrasound and Biochemistry in First‐Trimester Screening for Down's syndrome , 1997, Prenatal diagnosis.

[6]  K. Nicolaides,et al.  Maternal serum free β‐hCG at 10 to 14 weeks of gestation in trisomic twin pregnancies , 1997, British journal of obstetrics and gynaecology.

[7]  H. Cuckle.  Down's syndrome screening in twins , 1998, Journal of medical screening.

[8]  N. Wald,et al.  MATERNAL SERUM INHIBIN‐A LEVELS IN TWIN PREGNANCIES: IMPLICATIONS FOR SCREENING FOR DOWN'S SYNDROME , 1996, Prenatal diagnosis.

[9]  K. Spencer.  Screening for trisomy 21 in twin pregnancies in the first trimester: does chorionicity impact on maternal serum free β‐hCG or PAPP‐A levels? , 2001, Prenatal diagnosis.

[10]  K. Spencer.  Screening for trisomy 21 in twin pregnancies in the first trimester using free β‐hCG and PAPP‐A, combined with fetal nuchal translucency thickness , 2000, Prenatal diagnosis.

[11]  N. Wald,et al.  Maternal serum unconjugated oestriol and human chorionic gonadotrophin levels in twin pregnancies: implications for screening for Down's syndrome , 1991, British journal of obstetrics and gynaecology.

[12]  N. Wald,et al.  PRENATAL SCREENING FOR DOWN'S SYNDROME USING INHIBIN‐A AS A SERUM MARKER , 1996, Prenatal diagnosis.

[13]  K. Nicolaides,et al.  The lambda sign at 10–14 weeks of gestation as a predictor of chorionicity in twin pregnancies , 1996, Ultrasound in obstetrics & gynecology : the official journal of the International Society of Ultrasound in Obstetrics and Gynecology.

[14]  N. Wald,et al.  Erratum. Letter to the Editor: Inhibin‐A in Down's syndrome pregnancies: revised estimate of standard deviation , 1997, Prenatal diagnosis.

[15]  J. Haddow,et al.  MULTIPLE MARKER SCREENING FOR DOWN SYNDROME IN TWIN PREGNANCIES , 1996, Prenatal diagnosis.

[16]  N. Wald,et al.  Four‐marker serum screening for Down's syndrome , 1994, Prenatal diagnosis.

[17]  N. Wald,et al.  Integrated screening for Down's syndrome based on tests performed during the first and second trimesters. , 1999, The New England journal of medicine.

[18]  K. Nicolaides,et al.  Screening for trisomy 21 in twin pregnancies by maternal age and fetal nuchal translucency thickness at 10–14 weeks of gestation , 1996, British journal of obstetrics and gynaecology.