Screening for trisomy 21 in twin pregnancies in the first trimester: an update of the impact of chorionicity on maternal serum markers

Abstract

Objective To examine the distribution of first-trimester biochemical markers of aneuploidy in twin pregnancies, and to assess whether there are differences in the distributions between monochorionic and dichorionic twins.Methods Maternal serum-free β-hCG and PAPP-A were measured between 11 + 0 and 13 + 6 weeks as part of a routine first-trimester screening program in conjunction with fetal nuchal translucency (NT) performed at two sites. Data from twin pregnancies were extracted from the fetal databases along with information on the chorionicty. The individual marker concentrations were expressed as weight corrected, ethnicity corrected, smoking corrected and IVF corrected MoM using data from singleton pregnancies as the reference. The overall medians were compared to those in singleton pregnancies and between monochorionic and dichorionic twins.Results Data was available from 1914 sets of twins. Of these, 1214 had information with respect to chorionicity, with 1024 being dichorionic and 190 being monochorionic. The overall median weight corrected, ethnicity corrected, smoking corrected and IVF corrected MoM amongst twin pregnancies were 2.023 for free β-hCG (sd log 10 MoM = 0.2611 and 2.121 for PAPP-A (sd log 10 MoM = 0.2255)-both medians were significantly greater than the medians in singleton pregnancies (1.00 MoM). In the case of monochorionic and dichorionic twins the median weight corrected, ethnicity corrected, smoking corrected and IVF corrected, free β-hCG MoM's were not significantly different (1.983 v 2.041), however for PAPP-A the median weight corrected, ethnicity corrected, smoking corrected and IVF corrected MoM in monochorionic twins was significantly lower than in dichorionic twins (1.756 v 2.250) whilst the sd log 10 MoM's were not significantly different (0.2185 v 0.2167).Conclusion Screening in twin pregnancies requires adjustment of the calculated MoM to account for the presence of two fetuses. In general, for free β-hCG, this should be by dividing the observed corrected MoM by 2.023. For PAPP-A two different factors are required −2.192 in dichorionic twins and 1.788 in monochorionic twins.

Screening for Down syndrome in dichorionic twin pregnancies conceived by in vitro fertilization (IVF): a clinical pilot study to confirm the laboratory methods

“…This agrees with the predictions made by other authors using different methodologies [8][9][10][11]. Our secondary finding is that sonographic imaging together with the corrected maternal serum markers might improve the efficiency of the combined 11-14 week DS screening test in dichorionic twin pregnancies conceived after IVF when compared to the reference group.…”

“…In addition, the analysis demonstrated a 15 % closer approximation to the laboratory median for maternal serum-PAPP-A and a 10 % closer approximation for the maternal serum-free β-hCG in twins than in singleton pregnancies. Together these findings provide a new argument in favor of using the combined 11-14 week DS screening test in patients with DC twins conceived after IVF [6][7][8][9][10][11][12][13][15][16][17]. A new study with a larger sample size will be necessary to confirm that the laboratory corrections performed in the combined screening test improves the predictability of DS in dichorionic twin pregnancy conceived by IVF when compared to singleton control.…”

“…The combined 10-14 week screening test can be used in twin gestations [6][7][8][9][10][11][12][13]. This test combines maternal age, the sonographic measurements of the fetal nuchal translucency for the embryonic crown-rump length and the maternal serum concentration of PAPP-A and free-beta-hCG expressed in MoM for gestational age.…”

“…For these reasons, prenatal screening for common genetic syndromes should be offered to all women expecting twins. Indeed, in twin pregnancies the risk for Down syndrome (DS) can be calculated using the 11-14 week combined screening test where corrections for maternal weight, ethnicity, smoking, in-vitro fertilization (IVF), chorionicity, and age of the egg-donor are applied [8][9][10]. In this test, the likelihood of affected versus unaffected is Capsule For women with Dichorionic twins after IVF the combined first trimester test is an appropriate Down syndrome screening test.…”

Perinatal Mortality in Multiple Pregnancy

“…Screening in twin pregnancies requires adjustment of the multiple of the median (MoM) to account for the presence of two fetuses. Different factors are required for the observed corrected MoM for free β human chorionic gonadotropin and pregnancy-associated plasma protein-A (Spencer et al, 2008). The routine use of serum markers during first trimester is not recommended but their use is currently being assessed (Vayssière et al, 2011) …”