US citizens and foreign medical schools.

The foreign medical schools that are accepting an increasing number of applicants rejected by US medical schools are not comparable to US medical schools. Until population trends lessen the number seeking a medical education, several pathways are available to identify and assist the qualified student to return to US medicine.     

Estimates for the sensitivity and false-positive rates for second trimester serum screening for Down syndrome and trisomy 18 with adjustment for cross-identification and double-positive results

Second trimester screening for fetal Down syndrome and trisomy 18 is available through separate protocols that combine the maternal age-specific risk and the analysis of maternal serum markers. We have determined the extent to which additional Down syndrome affected pregnancies may be identified through trisomy 18 screening, and the extent to which additional cases of trisomy 18 may be screen-positive for Down syndrome. The combined false-positive rate, taking into consideration those pregnancies that are screen-positive by both protocols, has also been determined. Sensitivity and false-positive rates were determined by computer simulation of results that incorporated previously published statistical variables into the model. Using second trimester risk cut-offs of 1:270 for Down syndrome and 1:100 for trisomy 18, it was found that few additional cases of Down syndrome are identified through trisomy 18 screening. However, approximately 6-10% of trisomy 18 affected pregnancies will be screen-positive for Down syndrome but screen-negative for trisomy 18. For women aged 40 or more, the false-positive rate for trisomy 18 exceeds 1% and approximately half of these cases will also be screen-positive for Down syndrome. For a population with maternal ages equivalent to that in the United States in 1998, after adjusting for the cross-identification, the sensitivity for three-analyte trisomy 18 screening is 78%. If this testing is performed in conjunction with Down syndrome "triple" screening, the Down syndrome sensitivity is 75% and the combined false-positive rate is 8.5%. If the three-analyte trisomy 18 screening is performed with the Down syndrome "quad" screen, the trisomy 18 sensitivity remains at 78%, the Down syndrome sensitivity is 79%, and combined false-positive rate is 7.5%. Sensitivity and false-positive rates are also provided for other widely used Down syndrome and trisomy 18 risk cut-offs. Sensitivity and false-positive rates that take into consideration cross-identification and double-positives should be helpful for pre-test counseling and the evaluation of serum screening programs.     

Antenatal Down syndrome screening in the United States in 2001: a survey of maternal-fetal medicine specialists

OBJECTIVE: Our objectives were to determine patterns of antenatal Down syndrome screening and risk adjustment by maternal-fetal medicine specialists in the United States in 2001. STUDY DESIGN: A survey to investigate Down syndrome screening practice patterns was mailed to the 1,638 members of the Society of Maternal-Fetal Medicine in the United States. Practice demographics, screening patterns, and the numeric risks quoted in counseling were analyzed. RESULTS: Five hundred forty-three specialists (33.2%) responded; 530 of these specialists (97.6%) performed antenatal Down syndrome screening; all of them offered second-trimester screening, and 247 of them (45.5%) offered first-trimester screening. With the use of second-trimester ultrasonography, risk was increased by 69.4% of respondents and decreased by 33.1%. Amniocentesis was the most frequently used diagnostic test (83.2%), with loss rates quoted at 1:100 to 1:1,000. CONCLUSION: Maternal-fetal medicine specialists show a wide in variation practices used for Down syndrome screening, modification of risk, and quoted procedure-related loss rates. This information calls for a consensus regarding risks that are quoted in Down syndrome counseling.     

Cord blood sampling at delivery: do we need to always collect from both vessels?

The literature suggests that up to 19% of umbilical cord blood samples are invalid. Accordingly, it has been proposed that blood should be universally collected from both vessels. We prospectively collected paired arterial and venous blood to examine whether our centre, where staff were experienced in single vessel collection, was more accurate. Of 289 paired samples, 53 (18.3%) were considered invalid. Despite this significant error rate, we propose that routinely, only arterial sampling is needed and that an additional venous sample need only be taken to validate samples in cases of  pH < 7.15  , a difficult delivery or a non-vigorous baby.