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Re: Oligohydramnios, dolicocephaly and elevated AFPFrom: Lynn D. Montgomery, M.D. (apgar10@montanadsl.net)Thu Jun 23 11:19:45 2005
Jim, First, let me say that I am sorry you and your wife are having to deal with this stress and anxiety. Second, I would like to say that the opinions provided below are from the perspective of an MFM mentality and with my comments, I am not meaning to slight non-MFM individuals who may be excellent ultrasonographers or have technical expertise doing amnios - because I know there are some very qualified people who are not necessarily MFM's. 1. Estimated risk of amnio-infusion/centesis in the setting of oligo (AFI 5.6)? ** First, I dislike using absolute AFI numbers to quantify amniotic fluid volume at 18 weeks. AFI is primarily a later 2nd and 3rd trimester parameter. Most of the patients that get send to me with the diagnosis of oligo at this gestational age don't have it. Second, with pockets totaling 5.6 cm, this should be pretty easy to hit, obviously depending upon placental position, etc. As such, the risk typically quoted is 1/200 in general and the last study I read for MFM's was 1/350 (although I think it is less). In true oligohydramnios, one should be able to hit a 1 cm pocket. Finally, one of the primary risks of performing an amnio in true oligo is a cord stick (notice Bob that I didn't say "inadvertent" cord stick). If this occurs, the risk to the fetus is approximately 2.5% and the blood can be sent for karyotype. 2. Probability of finding spinal bifida or chromosomal abnormality in light of anatomically normal US? ** The most common chromosomal abnormality we see is trisomy 21 and the studies vary in the estimates regarding ultrasound detection, all the way from 50% to 85% - I personally think it is about 75%, missing 25%. With aneuploidy such as trisomy 13 and 18, the detection rate is much higher, some suggesting near 100% because there are typically more abnormal findings. As for neural tube defect, the ultrasound detection rate is in the neighborhood of 90-95%. 3. Utility of delaying any procedure at this time and repeating US in 2 and/or 4 weeks to see if more detailed anatomy can be visualized? ** Agree completely with Dan's response. It depends upon what you are going to do with the information. If termination is on the table, then pursuing testing is appropriate. If not, then waiting is certainly appropriate. 4. Optimal timing for amnio-infusion/centesis? **No time like the present. If there is indeed oligo, the fluid volume may decrease by waiting, thus increasing the technical difficulty and risk. Lynn
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