Antenatal screening

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

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.

Mid-gestation Down syndrome screening test and pregnancy outcome among unstimulated assisted-conception pregnancies

OBJECTIVES

Alteration of mid-gestation serum markers in assisted-conception pregnancies is believed to be attributable to ovarian superovulation treatment modalities. We compared alpha-fetoprotein (AFP), human chorionic gonadotrophin (hCG), and unconjugated estriol (uE(3)) in two groups of unstimulated assisted-conception pregnancies, that is, own-oocyte frozen embryos (own-FET) versus oocyte-donated (OD) embryos.

METHODS

Forty-three OD-conceived and 31 own-FET-conceived singleton parturient women (aged 29 +/- 4 years and 31 +/- 4 years respectively, P < 0.05) were followed from embryo transfer throughout pregnancy.

RESULTS

The daily pattern of first-trimester serum beta-hCG was similar in both groups. The OD group had only significantly increased AFP concentrations compared to the own-FET group (1.38 vs 0.99 median MoM respectively, P = 0.002). Although there were no chromosomal abnormalities and no fetal or neonatal deaths in either group, 12% OD women and 6.5% own-FET women were found screen-positive. Eight OD women and 11 FET women had an adverse obstetric outcome (P = NS).

CONCLUSION

OD embryos are a unique clinical model for evaluating the uterine compartment and its contribution to mid-gestation serum marker secretion.

Down's syndrome screening in pregnancies after assisted reproductive techniques: an update

Assisted reproductive techniques have increased the number of pregnant women beyond the age of 35 years and the incidence of multiple pregnancies. Various non-invasive screening methods for Down's syndrome were introduced in clinical practice during the past two decades. Specific problems were encountered when these methods were applied for pregnancies achieved by assisted reproduction treatment and the aim of this review is to explore these issues and propose an adjusted methodological approach for this highly selected population. Overall, more women with assisted reproduction singleton pregnancies are found to be false-positive for Down's syndrome. This is because standard screening algorithms include maternal age. In addition, mid-trimester maternal serum screening is associated with a higher false-positive rate. This is due to changes in the feto-placental endocrinological metabolism in pregnancies achieved by assisted reproduction treatment. Ultrasound screening of Down's syndrome by means of nuchal translucency (NT) measurements at 10-14 weeks is associated with a lower false-positive rate than mid-trimester serum screening. The lowest false-positive rates reported in singleton pregnancies are observed when serum and nuchal translucency screening are combined at 10-14 weeks. In multiple pregnancies, mid-trimester maternal serum screening is of limited clinical value. Nuchal translucency measurement is among the best available and is the most efficient screening method for multiple pregnancies. This sonographical method for screening enables specific identification of those fetuses at high risk of Down's syndrome and other anomalies, and thus contributes to a better outcome. Therefore, it should be systematically performed before any fetal reduction in high-order multiple pregnancies is planned.

Comparison of triple serum screening and pregnancy outcome in oocyte donation versus IVF pregnancies

The current study compared triple serum screening results and outcomes in 37 oocyte donation (OD) and 46 self oocyte IVF-conceived singletons of similarly aged women (28.8 +/- 4.4 years and 30.7 +/- 4.5 years respectively). Both groups were followed from their embryo transfer and throughout pregnancy. Although the daily pattern of first-trimester serum beta-human chorionic gonadotrophin (HCG) was similar in both groups, higher mid-gestation HCG serum concentrations were found, i.e. 1.38 and 1.32 multiples of the median (median MoM) for IVF and OD respectively, in comparison with 0.99 median MoM from the same reference laboratory. Only the OD group had significantly increased alpha fetoprotein (AFP) concentrations (1.45 median MoM) (P = 0.002) compared with the reference laboratory. A total of 11% of the IVF and 13% of the OD women were found to be screen positive. In neither group were chromosomal abnormalities detected and no fetal or neonatal deaths were recorded. Seven (15%) of the OD and seven (19%) of the IVF women had an adverse obstetric outcome. Of those cases, six IVF and four OD women had serum HCG > or = 1.2 MoM and five OD women had AFP >1.2 MoM. Therefore, in those pregnancies the high serum HCG concentrations may alert for adverse obstetric outcome rather than indicating a high risk for Down's syndrome fetuses.