Human chorionic gonadotrophin and alpha-fetoprotein levels in matched samples of amniotic fluid, extraembryonic coelomic fluid, and maternal serum in the first trimester of pregnancy

Abstract

Separately identified samples of amniotic fluid and extraembryonic coelomic fluid obtained by high resolution transvaginal ultrasound-guided amniocentesis from 32 women between 7 and 12 weeks of pregnancy were analysed for human chorionic gonadotrophin (hCG) and alpha-fetoprotein (AFP). There was a highly significant difference between the hCG levels in amniotic fluid (median level 6.3 U/ml; range 1.6-310.0 U/ml) and those in extraembryonic coelomic fluid (median level 400.0 U/ml; range 135.0-2250.0 U/ml) (p less than 0.001; Mann-Whitney U-test). The levels of AFP were very similar in amniotic fluid (median 26.0 kU/ml; range 10.0-116.5 kU/ml) and extraembryonic coelomic fluid (median level 24.1 kU/ml; range 12.4-94.4 kU/ml).

PIP: Physicians used transvaginal ultrasound to guide the aspiration needle into the amniotic fluid and extraembryonic celomic fluid from 32 women at 7-12 weeks gestation in St. Bartholomew's Hospital or Homerton Hospital in London, England. They also collected blood. Their intent was to determine the levels of alpha fetoprotein (AFP) [a fetal product] and human chorionic gonadotropin (hCG) [a placental product]. All of the these women had normal pregnancies, but were in the hospital to undergo a therapeutic abortion. Levels of hCG in the amniotic fluid stood significantly lower (median 6.3 U/ml) than those in the extraembryonic celomic fluid (400 U/ml; p.001). Serum levels of hCG were in between those in the fluids (75 U/ml). AFP levels in the amniotic fluid (26 U/ml) and extraembryonic celomic fluid ((24 U/ml) were not significantly different. No definitive trend in hCG or AFP levels with gestation in the 2 fluids occurred. A possible explanation for the higher levels of hCG levels in the extraembryonic celomic fluid may be that the extraembryonic celom is next to the chorion from where hCG originates. The amnion effectively separates the extraembryonic celom from the amniotic fluid. Perhaps the extraembryonic celomic fluid works as a sump for hCG. These results stress the importance of confirming the exact site of aspiration in the 1st trimester amniocentesis. Moreover, the transvaginal ultrasound is superior to the abdominal ultrasound in distinguishing between the 2 cavities since it has the necessary degree of resolution. It also is an effortless and precise method amniocentesis. These results also suggest that physicians can make and earlier diagnosis of neural tube defects since AFP leaks into its surroundings at a very early gestation.