question: Trisomy 18 (Exams and Tests): An exam during pregnancy may show an unusually large uterus and extra amniotic fluid. There may be an unusually small placenta when the baby is born. A physical exam of the infant may show unusual fingerprint patterns. X-rays may show a short breast bone.    Chromosome studies will show trisomy 18. The chromosome abnormality may be present in every cell or present in only a certain percentage of the cells (called mosaicism). Studies may also show part of the chromosome in some cells. Rarely, part of the chromosome 18 becomes attached to another chromosome. This is called translocation.   Other signs include:     - Hole, split, or cleft in the iris of the eye (coloboma)   - Separation between the left and right side of the abdominal muscle (diastasis recti)   - Umbilical hernia or inguinal hernia     There are often signs of congenital heart disease, such as:     - Atrial septal defect (ASD)   - Patent ductus arteriosus (PDA)   - Ventricular septal defect (VSD)      Tests may also show kidney problems, including:     - Horseshoe kidney   - Hydronephrosis   - Polycystic kidney