Nuchal translucency measurement and pregnancy outcome after assisted conception versus spontaneously conceived twins

BACKGROUND: Nuchal translucency (NT) measurement for Down's syndrome screening or detecting various fetal anomalies is a reliable sonographic marker. This study evaluates the contribution of NT screening in spontaneously conceived and assisted conception twin pregnancies. METHODS AND RESULTS: Maternal age at measurement, chorionicity, ultrasound features, karyotype results and pregnancy outcome were recorded prospectively and compared in 83 assisted reproduction treatment and 91 spontaneously conceived twins. Pregnancy outcome was evaluated according to maternal age, method of conception, NT data and chorionicity. NT measurements (greater than or equal to 95 centiles of the normal range) were considered screen-positive and mid-pregnancy fetal karyotyping was advised. Complicated pregnancy outcome, which could be signalled by increased NT, was defined as either chromosomal abnormalities, severe structural defects or fetal demise. Based on NT measurements, 16 fetuses (4.6%) were found to be screen-positive. Five of them had chromosomal aneuploidy and selective termination was performed. The parents also opted for this procedure in another five fetuses because of major structural abnormality diagnosed during NT assessment. No other chromosomal or major fetal abnormality were found post-natally. Although no difference was found in NT, crown-rump length and maternal age between spontaneous and assisted reproduction technology twin pregnancies, the former group had a significantly higher rate of screen-positive results (7 versus 2%, P=0.047), amniocentesis uptake (33 versus 22%, P=0.014), monochorionic twining (32 versus 4%, P=0.001) and complicated pregnancy outcome (11 versus 5%, P=0.02). CONCLUSION: The present study confirms that first trimester target scanning can improve outcome by early detection and management of cases with an anomalous co-twin. It also identifies some differences between spontaneously and artificially conceived twin pregnancies in relation to this area of testing.