The hCG␤ gene family contains six genes linked in tandem on chromosome 19 and labeled ␤ genes 7, 8, 5, 1, 2, and 3. Previous studies on a small number of placentas have indicated that ␤ gene 5 was the most highly expressed gene during the first trimester of pregnancy, followed by genes 3 and 8. ␤ genes 7, 1, and 2 were expressed at very low levels. The purpose of this study was to determine 1) whether this pattern of expression was typical during normal pregnancy by sampling a large number of

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... rst trimester placentas, and 2) whether there was a correlation between gestational age and the pattern of hCG␤ gene expression. Total RNA from 27 first trimester placentas varying in age from 6 -16 weeks was reverse transcribed into complementary DNA. The complementary DNA was amplified by PCR, and the amount of DNA representative of each hCG␤ gene was quantified by Genescan analysis. In 14 of the 27 placentas, hCG␤ gene 5 accounted for 50% or more of the total ␤ messenger RNA expressed. ␤ gene 3 was expressed at levels ranging from 1-42% of the total, and ␤ gene 8 expression ranged from 12-32% of the total. Gene 7 expression was less than 3% of the total ␤ expression in all 27 placentas. Although there appeared to be a trend toward lower expression of ␤ gene 3 in placentas beyond 10 weeks gestational age, there was no correlation of the pattern of ␤ expression with placental age. ␤ gene expression was also examined in two blighted ova, a spontaneous abortion sample, and a hydatidiform mole as well as in cultured JAR choriocarcinoma cells. With the exception of JAR cells, these abnormal tissues had low levels of gene 3 expression, but these levels were within the range of the patterns observed in normal placentas. These data suggest that it is the total amount of hCG␤ gene expression rather than the expression of individual ␤ genes that is important for the maintenance of normal pregnancy. (Endocrinology 138: 5459 -5465, 1997