Increased concentration of the free β‐subunit of human chorionic gonadotropin in hyperemesis gravidarum

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Abstract
Objective. The amount of free β subunit hCG (free β) has been reported to be increased in trophoblast disease and Down's syndrome, conditions also associated with high total hCG. Increased total hCG has been reported in hyperemesis gravidarum. We sought to determine if sera from singleton gestations with hyperemesis gravidarum contained a higher proportion of free β hCG compared to controls of comparable gestational age. Methods. Sera from 39 patients with hyperemesis gravidarum was compared with that from 23 control subjects of comparable gestational age with respect to β hCG and its subunits (free β and free α). Results. Hyperemesis patients and controls were comparable with respect to age, weight and gestational age. The concentration of hCG was greater in hyperemesis patients (9237 ± 3613 ng/ml, mean ± s.d.) compared to controls (5543 ± 2290, p < 0.005) as was the concentration of free β hCG (101±70 ng/ml vs. 31 + 31,p < 0.001). Free α did not differ between hyperemesis patients and controls (399±231 ng/ml vs. 377±214). A percent free β greater than 0.6 was found in 33/39 hyperemesis patients (85%) compared to 5/23 controls (22%),p < 0.001. Conclusion. Increased free β hCG is found in hyperemesis gravidarum. This finding, strengthens the association of hyperemesis with abnormal metabolism of hCG.