I am 18 weeks and 3 days pregnant with a little boy. Yesterday, at my ultrasound, they found a bright spot on his left ventricle and noticed that one of his legs measured at 17 weeks while his other leg and the rest of his body measured at 18 weeks. They are asking me to go in for another ultrasound next week to test for Down syndrome.
I am confused and want to know how worried I should be, or if the one week difference and bright spot will correct itself and everything will be fine? I am 23 years old and worried. Do we have a higher chance of having a baby afflicted with Down syndrome?
This is a hard question to answer without more information. Screening for Down syndrome is complex, because there is so much overlap between findings in babies with Down syndrome and what's seen in typical babies.
Several findings on an ultrasound are called "soft markers" for Down syndrome. These markers include some of the findings in your case—short femur (thigh bone) and "echogenic intracardiac focus" or EIC. Neither of these findings represents anything seriously the matter with the baby—they are just found more commonly in fetuses with Down syndrome. While most babies with these findings do not have Down syndrome, seeing these markers increases the odds that the fetus has Down syndrome. In order to know what increasing the odds means for you, you need to know your odds to start off with. If you had any other screening for DS this pregnancy you should already know what the chances were estimated to be before this ultrasound. If you didn't have any screening, you won't have this information.
In general, ultrasound is not considered an effective way to screen for Down syndrome. Families who want to be tested during the pregnancy are better off getting first trimester testing with blood work and ultrasound measurements of the fetal neck ("first check"), or second trimester blood testing ("quad screen"), or a combination of the two ("sequential" or "combined" testing). More recently, blood tests on the mom can actually find fetal DNA and directly test for extra chromosomes, like the extra chromosome 21 of Down syndrome. This is called Noninvasive Prenatal Testing (NIPT). All of these tests are much better at assessing the chance of Down syndrome than ultrasound is. If you already had this sort of testing, the ultrasound findings might increase your chances slightly, but often not enough to make any difference. Your doctor or midwife, or a genetic counselor, should be able to help you understand what this means and decide whether further testing is indicated.