Urinary hCG patterns during the week following implantation.
BACKGROUND
Human chorionic gonadotrophin (hCG) is used to monitor pregnancy status. Yet the pattern of hCG excretion in the first week following implantation has not been adequately described. Therefore the aim of this study was to describe the average profile of hCG and its variability during the 7 days following estimated implantation in a population of naturally conceived pregnancies.


METHODS
We measured daily hCG concentrations in first-morning urine for 142 clinical pregnancies from women with no known fertility problems. Mixed-effects regression models were used to estimate the hCG trajectory and its variability in relation to pregnancy outcomes.


RESULTS
hCG rose 3-fold between the day of detection and the next day (95% CI = 2.7-3.4). The relative rate of rise decreased thereafter, reaching 1.6-fold (95% CI = 1.5-1.8) between days 6 and 7. HCG levels followed a log-quadratic trajectory, and the patterns of rise were unrelated to number of fetuses, risk of spontaneous abortion or sex of the baby. Later implantations (after 10 luteal days) produced slower rates of increase.


CONCLUSIONS
Although mean hCG follows a log-quadratic trajectory during the first week of detectability, there is high variability across pregnancies. Later implantation may reflect characteristics of the uterus or conceptus that slow hCG production.
Nepomnaschy
P A
PA
Epidemiology Branch, National Institute of Environmental Health Sciences, National Institutes of Health, Department of Health and Human Services, Research Triangle Park, NC, USA. pablo_nepomnaschy@sfu.com
Weinberg
C R
CR
Wilcox
A J
AJ
Baird
D D
DD
D000022:Abortion, Spontaneous / Q000652:urine; D000328:Adult; D006063:Chorionic Gonadotropin / Q000652:urine*; D010064:Embryo Implantation; D005260:Female; D005333:Fetus; D006801:Humans; D008499:Medical Records; D009994:Osmolar Concentration; D011247:Pregnancy / Q000652:urine*; D011272:Pregnancy, Multiple / Q000652:urine; D012737:Sex Factors; D013997:Time Factors; D014427:Twins
D006063:Chorionic Gonadotropin