Venous lakes are unusual in the first trimester, however, when identified in a low lying position near the cervical os, we believe they represent a relative contraindication to chorionic villus sampling.doi:10.7863/jum.1988.7.5.297Pozniak, M A...
Indeed, The oval foramen (called also ostium secundum of Born) is an interatrial congenital anatomical communication, allowing during the intra-uterine life, the passage of oxygenated blood from the placenta; from the right atrium to the left atrium; thus towards the large systemic circulation. Aft...