Introduction
Birth defects (BDs) are identified in approximately 1 in 300 women who undergo a routine third trimester ultrasonographic scan1, and the global prenatal diagnosis rates vary from 15% to 86%, according to region, BD category, and the method of diagnosis.2-5 With the rapid development of the technology for prenatal examinations, a wide range of methods have become available that improve the prenatal diagnosis of BDs. These include prenatal ultrasonography, biochemical screening, invasive techniques such as amniocentesis and chorionic villus sampling (CVS), non-invasive prenatal testing (NIPT) using cell-free fetal DNA, and gene diagnose, as well as autopsy.6, 7
The prevalence of multiple birth in China and internationally has been increasing, such that it is now between 0.9% and 3.3% worldwide.8-13 This can be, at least in part, attributed to advancing maternal age and the use of assisted reproductive technologies (ARTs). The accurate prenatal diagnosis of BD associated with multiple pregnancy remains challenging, but few studies have been conducted. Club foot, Down syndrome, and trisomy 18 have been reported to be less frequently diagnosed in twins than in singleton fetuses,14-18 whereas Boyle et al. showed that multiple and singleton pregnancies were associated with comparable rates of prenatal diagnosis.19 The methods used for prenatal diagnosis often differ for singleton and multiple pregnancies. For example, the ultrasonographic survey of general anatomy and echocardiography for the identification of congenital heart disease are recommended for twins. However, a prenatal diagnosis of aneuploidy is commonly made on the basis of the analysis of maternal serum markers, which is not specific for a particular fetus.18,20 In addition, most previous studies were of small numbers of twins with specific malformations and used specific screening methods that can be affected by differences in technical skill level and up-to-date knowledge.
In Zhejiang, a province located in eastern China, the prevalence of twin births increased from 2.27% in 2008 to 3.01% in 2013.11 A provincial BD surveillance system has existed there for over 30 years, and this provides a useful platform for BD-related researches. In this study, we compared the prenatal diagnosis of BDs for singleton and multiple pregnancies. We anticipate that the findings should assist the prenatal diagnosis of BDs, especially in women with multiple pregnancies.