ULTRASOUND Messages for November, 2005: Re: mid-term femur length trisomy risk query

Re: mid-term femur length trisomy risk query

From: James Smeltzer

James.Smeltzer@wellstar.org

Thu Nov 17 05:57:25 2005

Bernacerraf's group has studied this extensively. The use of isolated single measures to positively predict Down's Syndrome sonographically is not reliable, except the positive predictive value of atrioventricular septal defect (Downs vs field 2:1), duodenal atresia or web (1:2). The physiognomy, body type, arms, legs, hands, feet of a fetus should always be referenced to parents if possible, but very short is high risk, even with short parents IMHO.

The problem is that a 40 y/o woman has a prior risk of 1/50, change to about 1/200 by nuchal lucency.

Please check and comment on: nose bone (missing or small very common, upturned common), head shape (brachycephalic very common), ear length (short, low, simple very common), facial appearance especially mid-face projection (flat extremely common) and overall shape (round very common), current nuchal thickness (thickened common), humerus length (short very common), digits hand: (simian crease reported, but I have never seen it) (phalanges graduated stacked box appearance very common), especially 5th finger (clinodactyly with small and wedged MP of 5 is very common) and 1st toe (wide space very common), (short, wide feet very common), four-chamber heart, especially atrial dimensions of right vs left (right predominance in 85% by DeVore very common) and crux (straight across or missing in AV canal 5% but highly predictive), other heart defects effusions or hydrops (common - 50%, but less prenatally), umbilical artery (single uncommon but predictive), stomach appearance (double bubbles uncommon but predictive: one-third have DS), kidney appearance (renal pelvis dilation, mild common), bowel appearance (bright occasional but predictive), pelvis width (wide max outer to outer ilial diameter vs femur length common) and angle (>45 degrees, not reproducible by some common).

We are starting on the wrong end of this equation, IMHO. People not only come in all shapes and sizes, they also have all kinds of dispositions. Do they wish prenatal diagnosis? If not, you are done unless there is a gross heart or other defect or hydrops. Is targeted imaging and expert counselling available? If so, they need it. Do they wish certainty regarding chromosomes? Is she losing sleep over this? Would she have an abortion? If so, needs amniocentesis.

I will never forget the 35 year-old woman I cared for years ago in St. Louis. Missouri medicaid would not pay for prenatal genetic diagnosis. My chief, the late honorable Klaus Staisch, believed that providing this service was standard of care even in an indigent care hospital. The hospital ate the $700 a pop that Jim Crane charged us for the chromosomal evaluations - no discounts. You better believe we provided structured counselling. This woman desired amnio despite a negative sonogram. The results returned trisomy 21. I rescanned her with the results in hand, and the sonogram was normal. She carried the pregnancy. When the baby was born, I asked Corinne Valentik, our neonatologist, if the baby had a heart defect I had missed. SHe asked "What baby?" I said the one with Down's. She said that there was no baby in the nursery with Down's. I pointed the baby out to her and she said the baby did not have Down Syndrome: there was no sign of Down Syndrome. I said I had known that for five months, but it did not change the chromosomes. She was so skeptical she repeated them in a different lab. The results were the same, Trisomy 21.

That baby taught me that dysmorphology only goes so far. The number and appearance of chromosomes is a fact. When you are only interested in that fact, the chromosomes are the things you should look at. When we can consistently and accurately harvest fetal cells at reasonable cost from maternal blood I will be out of that business. Until then, I enjoy the prenatal diagnosis and am happy that so far this is the only miss so far, and that my positive amnio rate for chromosomal abnormalities is between 20 and 35 percent. But I will never have a problem doing an amnio when the patient wants this certainty.

"When all you have is a hammer, everything looks like a nail" ... (anonymous) ;^) Jim Smeltzer

-- James S. Smeltzer, MD, FACOG, SMFM Consultant, Maternal Fetal Medicine Wellstar Physicians' Group Northwest Women's Care 787 Campbell Hill St Marietta GA 30060 James.Smeltzer@wellstar.org VM 678-290-3035 Off 770-528-0260 Page 404-318-3451

>>> fizztastic@talk21.com 11/15/2005 2:33:46 PM >>>

The patient is 40 years old; her partner is 50. This is their first pregnancy. They are very concerned about age-related risk of chromosomal abnormalities, but opted against CVS and then amnio when 1st trimester screening adjusted their background trisomy 21 risk to 1:272 and trisomy 13/18 risk to 1:843.

The mother is above average height (183 cm) and the father is below average height (168 cm). Both are Causasian. My question is this: at 21 weeks + 3 (dated by known LMP), the femur length of the fetus is 33.5 mm. (Other measurements taken at the same time include BPD 53 mm; HC 182 mm; TCD 21 mm; CM 5 mm and AC 161 mm.) Is this low enough to warrant concern? Urgently seeking advice. Any comments would be gratefully received. Thanks very much.

Mary

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