Current concepts of Down syndrome screening tests in assisted reproduction twin pregnancies: another double trouble

Abstract

Assisted reproductive technologies (ART) have increased both the number of pregnancies in women beyond the age of 35 and the incidence of multiple pregnancies. Various methods of screening for Down syndrome (DS) were introduced in clinical practice during the last two decades, and specific problems were encountered when they were applied for twin pregnancies. The current review aims to explore the problematic issue of prenatal DS screening in ART twins. Overall, more women with twin pregnancies (mainly those who conceived via assisted reproduction) are found to be false positive for DS. This is because mid-trimester maternal serum screening is associated with a higher false-positive rate secondary to changes in the feto-placental endocrinologic metabolism, reflected mainly in high human chorionic gonadotrophin (hCG) levels in the ART pregnancies. First-trimester nuchal translucency (NT) measurement in twin pregnancies is not affected by the problems encountered in serum screening. This sonographic screening approach enables a fetus-specific identification of those fetuses at high risk of DS and is associated with a lower false-positive rate than mid-trimester serum screening. DS screening in ART twins presents several challenges in determining the most appropriate screening test modality. Whether there is any significant benefit of adding first-trimester biochemistry or nasal bone scanning in screening ART-conceived twins awaits further investigation.

Maternal serum free‐β‐chorionic gonadotrophin, pregnancy‐associated plasma protein‐A and fetal nuchal translucency thickness at 10–13+6 weeks in relation to co‐variables in pregnant Saudi women

“…In the present study, there was no significant difference in the median fetal NT MoM values between singleton and twin pregnancies among the pregnant Saudi women examined. These findings are consistent with previous studies (Maymon et al, 2005;Hui et al, 2006). Moreover, twin pregnancies showed higher biochemical marker values for median MoM as compared with singleton counterparts: free β-hCG (b 1.92-fold) and PAPP-A (by 2.23-fold).…”

Impact of chorionicity on first‐trimester nuchal translucency screening in ART twin pregnancies

“…The group of Maymon et al . did not find significant differences in median NT and mean NT MoM values between ART ( n = 128) and spontaneous twin pregnancies ( n = 70) . Likewise, Gonce at al .…”

“…The group of Maymon et al did not find significant differences in median NT and mean NT MoM values between ART (n = 128) and spontaneous twin pregnancies (n = 70). 20 Likewise, Gonce at al. reported similar median NT MoM in 84 twins with spontaneous conceptions and 122 assisted conception twins.…”

“…Although small deviations of NT thickness have been shown compared with spontaneous singletons in some studies, this had no impact on overall screening performance. The subject of NT screening in ART twins is less well investigated in the literature . Especially chorionicity as an important confounding variable is infrequently addressed …”

“…The subject of NT screening in ART twins is less well investigated in the literature. 20 Especially chorionicity as an important confounding variable is infrequently addressed. 16,21 Therefore, the aim of the present study was to assess the possible differences of NT thickness in twins following ART compared with spontaneous conception in a large cohort and to differentiate results with regard to chorionicity.…”