Main findings
Although the findings made to date regarding the incidence of BDs
associated with multiple and singleton pregnancies have been
inconsistent, most studies have shown that multiple pregnancies are
associated with a higher risk of BD than singletons.23,
24 However, univariate analysis alone was performed in the previous
studies, and they did not categorize the BDs and had small sample sizes.
In contrast, we studied multiple types of BD and the study had a large
sample size of more than 1.9 million births, which should have
facilitated the drawing of reliable conclusions. We found that multiple
pregnancy is associated with a significantly higher risk of and a lower
prenatal diagnosis rate for BDs than singleton pregnancy.