If your pregnant patient is a vegetarian, be aware of the fact that she may test false positive for Down syndrome. In fact, she is about three times more frequently than omnivores and reference pregnancy populations to have falsely elevated hCG readings, according to a study from Taiwan.
Researchers studied over 200 lactovegetarian and omnivore singleton pregnancies and found that midtrimester maternal serum free ß-human chorionic gonadotropin (ß-hCG) levels were elevated in the vegetarian pregnancies, which led to the higher false-positive rate in Down syndrome screening. The elevation in maternal serum free ß-hCG was especially pronounced in vegetarian women with low serum vitamin B12 levels.
As a result, the authors emphasize the importance of adequate vitamin B12 for all pregnant women, but especially those who are vegetarians. In addition, they posit that Down syndrome screening in vegetarian pregnancies be accomplished through ultrasound markers and nuchal translucency measurement to avoid invasive confirmation procedures, at least until reference biochemical marker levels for hCG are established for vegetarian pregnancies.
Cheng PJ, Chu DC, Chueh HY, et al. Elevated maternal midtrimester serum free ß-human chorionic gonadotropin levels in vegetarian pregnancies that cause increased false-positive Down syndrome screening results. Am J Obstet Gynecol. 2004;190:442-447.