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. Copyright © 2005 John Wiley & Sons, Ltd.     

Ethmocephaly caused by de novo translocation 18;21—prenatal diagnosis

Ethmocephaly is a rare anomaly associated with partial failure of cleavage of the prosencephalon. Morphologically, it is closely related to cyclopia. We present an extremely rare case of ethmocephaly diagnosed in utero and caused by an unbalanced de novo translocation 18;21. Copyright © 2003 John Wiley & Sons, Ltd.     

Does a ‘notched’ nuchal translucency indicate Down syndrome fetuses or other adverse pregnancy outcome?

The aim of the present study was to assess the sonographic contour of the increased nuchal translucency (NT) and to correlate this with pregnancy outcome. Fifty sonographic images of fetuses with increased NT [>95th centile thickness of the normal range for crown–rump length (CRL) between 38 and 84 mm] were retrospectively assessed. In all the cases a complete pregnancy and even infancy follow-up (<36 months) was available. The NT appearances were subdivided into two forms: a ‘notched’ or ‘uniform’ appearance. The images were correlated with karyotype results [trisomy 21 (DS) vs euploid cases] and pregnancy outcome. Complicated outcomes were classified as being either DS fetuses, miscarriage or termination of pregnancy because of structural anomaly. Thus 30/35 (86%) of the euploid fetuses had a ‘uniformly’ increased NT, whereas 8/13 DS cases (62%) had a ‘notched’ appearance (Fisher's exact test, p=0.004). Additionally, 27/29 fetuses (93%) which had an uneventful pregnancy outcome had a ‘uniform’ increased NT, whereas 12/26 (57%) of the fetuses which had adverse pregnancy outcome had a ‘notched’ appearance of their NT (Fisher's exact test, p<0.001). Although it was not possible to correlate the sonographic data with post-evacuation microdissection findings, it is possible that a uniformly shaped, increased NT may be more representative of a developmental delay in a normal fetus. Conversely, a ‘notched’ nuchal surface may represent abnormal lymphatic or cardiovascular development more commonly seen in DS fetuses. Copyright © 2001 John Wiley & Sons, Ltd.     

Solar energy harvesting in the epicuticle of the oriental hornet (Vespa orientalis)

The Oriental hornet worker correlates its digging activity with solar insolation. Solar radiation passes through the epicuticle, which exhibits a grating-like structure, and continues to pass through layers of the exo-endocuticle until it is absorbed by the pigment melanin in the brown-colored cuticle or xanthopterin in the yellow-colored cuticle. The correlation between digging activity and the ability of the cuticle to absorb part of the solar radiation implies that the Oriental hornet may harvest parts of the solar radiation. In this study, we explore this intriguing possibility by analyzing the biophysical properties of the cuticle. We use rigorous coupled wave analysis simulations to show that the cuticle surfaces are structured to reduced reflectance and act as diffraction gratings to trap light and increase the amount absorbed in the cuticle. A dye-sensitized solar cell (DSSC) was constructed in order to show the ability of xanthopterin to serve as a light-harvesting molecule.     

Bulk carbon, oxygen, and hydrogen stable isotope composition of recent resins from amber-producing Hymenaea

Resins of Hymenaea, an angiosperm tree genus known to be a copious resin producer and a major source of amber since the Oligo-Miocene, were collected from a wide range of tropical environments from Latin America and Africa, and analyzed for their carbon, hydrogen, and oxygen stable isotope composition. The average value for ¹³C in the resins was found to be –27.0±1.3, which is very similar to the values reported for resins in other studies. ¹⁸ values for the Hymenaea resins averaged +11.2±1.6, or about 20 more depleted than normal plant cellulose. D values of the resins ranged from –196 to –319, with an average of –243±30. Rough estimates suggest a fractionation of –200 to –210 between the resins and the environmental water. This value is similar to the –200 value observed for the fractionation between other plant lipids and environmental water. The present study suggests that the stable isotope composition of fossil resins (amber) has the potential to provide information on ancient environmental waters.