Hello Dr. T: I am also new to the whole blogging thing. I am currently 13 weeks 3 days, and was told at my last prenatal appointment that based on my first trimester screening, I have a 1 in 235 chance of having a baby with Downs syndrome. I am only 23 years old, and I wasn't sure if this is horrible. I thought most people had a 1 in 275 chance, but looked it up online and came to find out that it’s more like 1 in 1200, so naturally was very concerned. I was wondering if you could shed some light on this whole odds thing, because I'm sort of freaking out. I do have kidney disease MPGN type 1 and Graves disease, not sure if that makes a difference. I have one other child he's 4 and very healthy, with no disabilities whatsoever. Hope you can help me understand this a bit more. Thanks
To Leilani: The risks for having a baby with Down syndrome and many other chromosomal abnormalities resulting from nondisjuntion increase with age with the actual risks also varying by pregnancy trimester. At your age your chance of delivering a baby with Down syndrome is only about 1 in 1250 and the chance of having a baby with any chromosomal abnormality only about 1 in 500. The first trimester chances that the baby could have a chromosomal abnormality are 20-30% greater than these because such babies have a higher chance of getting lost along the way. Your 1 in 235 risk based on the first trimester screening is equivalent to that of a 35 year old woman in first trimester. Hear me loud and clear, however, just because the risk screening result is therefore ‘abnormal’, that does NOT mean the baby necessarily has Down syndrome. Indeed, it has a 234 out of 235 chance (>99%) that it does not.
You did not tell me the actual results of your tests, but it is possible that your kidney disease skewed the risk assessment if you are not clearing the serum analytes (hCG and PAPP-A) normally, particularly the hCG. Indeed, if you have membranoproliferative glomerular nephritis (MPGN), that is often associated with decreased kidney function and about 20% of the pregnancy hormone hCG is typically excreted by the kidneys (that’s why you can do a pregnancy test on urine samples). If this led to a higher circulating hCG level, that might increase your 'risk' for Down syndrome but not the chance the baby actually has it.
If on the other hand (or in addition to), the PAPP-A level is on the low side, that might further increase your ‘risk’ for Down syndrome. Your kidney disease is an autoimmune condition in which your own antibodies attack the kidneys and cause activation of a series of chemicals called the complement system. Complement helps to further damage anything the antibodies attach to (and normally it is a very important means of fighting off organisms that cause infections). However, unlike hCG, PAPP-A clearance does NOT seem to be impaired in some patients with autoimmune kidney disease (Rysavá, et al., Kidney Blood Press Res 2007;30:1-7) and therefore your kidney disease might lead to an elevation of the hCG alone when compared to the PAPP-A levels. The greater the difference in the multiples of the median (MOMs) of those two pregnancy products, the greater your calculated ‘risk’ for Down syndrome.
You should also be aware that women who have autoimmune diseases, particularly those that affect the kidneys, are also at greater risk for having an abnormal placenta – a small and/or a poorly vascularized placenta – that can eventually lead to poor fetal growth, hypertensive disorders of pregnancy (preeclampsia), and need for early delivery. This could further reduce your PAPP-A out of proportion to the hCG (which is also made by the placenta) and increase the Down’s risk even further.
It is true that young women can have babies with Down syndrome and indeed, about two-thirds of babies with chromosomal abnormalities are actually born to women at low risk based on age alone. However, in your case, I am betting on your risk being elevated because of your autoimmune kidney disease. My suggestion would be to 'lay low' for a bit and simply have a good genetic sonogram done at about 18 weeks. If that is normal, it will reduce your ‘risk’ by at least 50%. Of course, you always have the option to have an amniocentesis done at 15-16 weeks if you just have to know for sure as soon as possible. Best wishes and let us know how things turn out. Dr T