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The following questions were asked during the workshop. Results of the MedLine reference review follow the questions.
Umbilical cord twisting is believed to be related, at least in part, to fetal activity. Therefore, with a more active fetus, a more twisted umbilical cord is expected and conversely, with a more sedate fetus, a poorly twisted cord is expected. (1) In the early 1990's, Dr. Strong and his colleagues attempted to quantify this relationship, by first confirming what others had observed, that a child born with non-coiled umbilical vessels is at increased risk for perinatal morbidity and mortality (2). They then developed the "umbilical cord index" (divide the total number of complete vascular coils by the length in centimeters of the umbilical cord) (3) to quantitate umbilical vascular coiling, revealing the mean umbilical coiling index to be 0.21 +/- 0.07 (SD) coils per centimeter. Dr. Strong et al discovered an association between increased incidence of abnormal karyotype, meconium staining and need for operative intervention for fetal distress and umbilical coiling index below 0.10, and that moderate to severe variable fetal heart rate decelerations were associated with both decreased umbilical coiling index below 0.10 and above 0.30. If the umbilical coiling index was to be of clinical value, Dr. Strong recognized the importance of being able to determine cord coiling antepartum. By studying prenatal ultrasounds, he discovered that although 30% of noncoiled cords early in gestation will become coiled by delivery, the 2-6% of cords that remain uncoiled throughout gestation can be recognized on ultrasound, and may represent a real risk for suboptimal perinatal outcome. Dr. Strong et al also discovered that cords with umbilical coiling indices of less than 0.10 were at greater risk for nuchal entanglement. (5) These 4 articles (2, 3, 4, 5) also discuss the fiber structure of the cord, the possible etiology of umbilical cord twisting and the possible protective function of the coiled cord.
In their straight forward and succinct article, Dr. James Thorp and Dr. R Scott Rushing (6) review "the issues surrounding the use of umbilical blood gas analysis, including pertinent acid-base physiology, techniques, normal value, perinatal factors affecting the values, and controversies surrounding universal and selective sampling strategies." "Which Umbilical Vessel Should Be Sampled?" suggests umbilical artery blood most accurately reflects the condition of the fetus, because it is the blood returning from the fetus versus the umbilical vein which carries the blood from the placenta to the fetus. However, umbilical venous blood gas measurements better reflect maternal acid-base status and placental function, in addition to fetal acid-base status. If only one vessel can be sampled, it should be the umbilical artery; however sampling from both an artery and the vein may be associated with some advantages, perhaps providing insights into the cause of an acid-base disturbance.
Dr. Charles Canver, in his 1995 article "Conduit Options in Coronary Artery Bypass Surgery" (7), reported that although glutaraldehyde preserved umbilical vein grafts are well suited to withstand high arterial pressures and wall tension because of their circumferential elasticity and are readily available and easily stored, their usefulness as a coronary artery bypass graft is somewhat limited due to 1) the fact it remains a foreign material despite glutaraldehyde fixation which alters its immunogenicity; 2) dissection of the innermost layer of the vein occurs easily; and 3) the patency rate is low, with short-term patency of only 50%. However, "the umbilical vein graft has become an effective alternative to autogenous material" for lower extremity revascularization, allowing limb salvage rates of up to 68% for crural reconstruction and 80% for popliteal reconstruction, according to Kurt Wengerter and Herbert Dardik. (8)
According to the 1998 PDR (9), for Ortho Diagnostics MICRhoGAM (50 micrograms) and RhoGam (300 micrograms) and Bayer Corporation's BAYRHO-D Mini-Dose (50 micrograms) and BAYRHO-D Full Dose (300 micrograms), a lesser dose (50 micrograms versus the full dose of 300 micrograms) of Rho(D) immune globulin is given after a spontaneous or induced abortion, termination, or ectopic pregnancy up to and including 12 weeks gestation, to prevent isoimmunization in the event fetal-maternal/transplacental hemorrhage of greater than 0.1 ml of fetal red blood cells into the maternal circulation occurred at that time. Even though fetal red blood cell production is not well developed until about 20 weeks gestation, fetal red blood cells are present from early gestation. Although the total fetal red blood cell volume before 12 weeks is estimated to be less than 2.5 ml, there is a 3% risk of maternal isoimmunization. After 12 weeks gestation, regardless of the indications, a full dose of Rho(D) immune globulin is required. References
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