Placental mRNA expression of alpha and beta human chorionic gonadotrophin in early trisomy 18 pregnancies.

The placental expression of human chorionic gonadotrophin (HCG) I- and beta-subunits was investigated in eight pregnancies presenting with trisomy 18 and in 30 normal pregnancies at 11-15 weeks gestation. In the control group, the median densitometric scores of placental beta-HCG and I-HCG mRNA were 1.23 and 1.74 respectively. In the trisomy 18 group the median beta-HCG mRNA was significantly lower (0.16, Z = 2.29, P < 0.05) but alpha-HCG [0.60, Z = 1.75, P = 0.08) was not significantly different from normal. These findings suggest that in trisomy 18 the decrease in maternal serum concentration of HCG subunits results from an impairment in the transcription of the corresponding gene which affects the beta subunit to a greater extent than the I subunit.