Elevated maternal midtrimester serum free β-human chorionic gonadotropin levels in vegetarian pregnancies that cause increased false-positive Down syndrome screening results

Objective The aim of this study was to examine whether midtrimester maternal serum free β-human chorionic gonadotropin and α-fetoprotein levels for Down syndrome screening differed in vegetarian pregnancies and omnivore pregnancies and to evaluate whether maternal serum vitamin B12 concentration affected these maker levels. Study design Ninety-eight vegetarian and 122 omnivore singleton pregnancies were studied. Reference levels of free β-human chorionic gonadotropin and α-fetoprotein were based on a population of 6312 singleton euploid pregnancies that had been surveyed previously. Serum free β-human chorionic gonadotropin and α-fetoprotein levels were measured by enzyme immunoassay or radioimmunoassay. Multiples of the median values were calculated to determine whether different diet habits affected serum biomarker levels. Maternal serum vitamin B12 levels were determined with radioimmunoassay. Results The free β-human chorionic gonadotropin multiples of the median values were elevated significantly in the vegetarian pregnancies group (1.28 multiples of the median) compared with that of the reference population (1.00 multiples of the median) (P<.001). A negative association between the serum free β-human chorionic gonadotropin multiples of the median values and the concentration of maternal serum vitamin B12 was observed in the vegetarian pregnancies. No correlation was found between the α-fetoprotein multiples of the median values and the maternal serum vitamin B12 concentration. Conclusion The current data showed that the midtrimester maternal serum free β-human chorionic gonadotropin levels increased in vegetarian pregnancies and led to an elevated false-positive rate in screening for Down syndrome compared with pregnant women with regular diet and resulted in unnecessary invasive procedures. It is necessary to establish vegetarian pregnancy α-fetoprotein and β-human chorionic gonadotropin reference levels to correct increased false-positive screening results.