Understanding Abnormally Thick Placenta During Pregnancy: Causes & Concerns

Question
I am 25 years old and my fiancee is 30 years old. We have one healthy son who is 16 months old. (No pregnancy complications)I am a non- smoker but my fiancee is a smoker but I try to limit his smoking around me. Presently, I am 35 weeks pregnant and my OB informed me after a second ultrasound to determine the position of the baby that my placenta is 6 cm thick. My last period was in May of 2005 and I am due at the end of February. They referred us to a maternal fetal specialist for testing. My fiancee does have another healthy son and a daughter with Down Syndrome from his first marriage. Both he and his ex-wife were told by the hospital that they were not carriers and neither of them have a family history of Downs. Naturally, I was tested for Downs and the tests were negative. My ultrasound pics are normal except for the thick placenta. The fetus (girl) measures and weighs (5lbs. 3ounces at 33 weeks) according to the doctors, exactly what she should for her gestational age. I have been tested for diabetes and sexually transmitted diseases and all were negative. I am also being tested for an intrauterine fetal infection. I had a rash in my second trimester that is fading now. Some one thought it looked like erythema but the doctors never said it was anything other than a rash. It was accompanied by mild itching. I am tired and I accquired edema in my ankles at 33 weeks. I am in very good health and not overweight and my blood work has been fine. I was hoping that you might be able to inform us any other problems that may arise from a placenta of this size. I have looked on-line and found disorders like fetal hydrops, PMD (very rare), toxoplasmosis for enlarged placentas. I do have a house cat and I do change her litter box. I am just trying to be informed and educated about the possibilities of birth defects for our unborn child. At this point, the doctors haven't said anything one way or the other. Thanks for the info.  

Answer
I do not believe that a slightly thicker placenta will have any effect on the fetus as long as it is adequately growing and the FH is good. Everything you describe appears to be within normal limits. Often, a placenta can be thicker as a result of some other problem, which you do not appear to have. I wouldn't worry about it. When the baby is born, he will be checked out by the pediatrician. See what the perinatologist thinks, too, and let me know what is said.