Thiamin status in pregnancy as determined by direct microbiological assay.

Serum and red cell thiamin levels were assayed on a group of pregnant Australian women using an automated direct microbiological assay with Lactobacillus fermenti as the test organism. Two of 103 (1.9%) had serum thiamin levels below the reference range and 2 of 67 (3.0%) were found to have red cell thiamin levels below the reference range. Although the mean serum levels between trimesters were not significantly different, there was a significant decrease in the mean red cell thiamin in the third trimester. Repeat red cell thiamin assays on some of the women a number of weeks after the initial assay revealed a decrease ranging from 17.5% to 35.4% with a mean reduction of 27.8%.