Relationship between human chorionic gonadotropin(HCG) and pregnancy weeks

Eight days after conception, hCG can be detected in the maternal circulation; a concentration of approximately 10 mlU/ml is observed in serum between 9 and 10 days after follicular rupture. As the pregnancy develops, the level of hCG increases at a rate of approximately 50 % per day, reaching a peak of around 100 000 mlU/ml by week 10, after which levels decrease and remain stable at approximately 20 000 mIU/ml for the remainder of the pregnancy.

In addition to being present in maternal serum, hCG can be detected in the urine of pregnant women, where its appearance and rise show similar patterns to those observed in the maternal circulation. At 9 days after conception, the mean concentration of hCG has been observed to be 0.93 mIU/ml, with levels increasing daily until they reach the plateaux at approximately 45 days post conception.

This daily increase in urinary hCG levels by approximately 50 % observed in early pregnancy was consistently noted in different studies conducted across a 5-year period, using three different cohorts of women, as shown in?Fig. 1. All of the studies reported a remarkable uniformity in the rise of hCG levels in early pregnancy. This combined cohort data has been used to provide reference ranges for hCG for each day of pregnancy (Table 2). The studies reported no differences between ethnicities with regard to urinary hCG increase. However, levels of serum hCG in early pregnancy (day 16 following assisted reproductive technology [ART]) have been seen to be slightly lower in women with a higher pre-pregnancy body mass index (BMI); this may be due to the effect of adipose tissue-derived signaling molecules on hCG secretion by the implanting embryo.

Fig. 1Daily increase in urinary hCG in early pregnancy in three different studies: The UK Early Pregnancy Study?, the UK Standard Care Ultrasound Study?and the US Gestational Age Study. The grey area is the 10th to 90th centile band for the US Gestational Age Study.

Table 2 below: Reference ranges for urinary intact hCG for each day of pregnancy. Duration of pregnancy refers to days since ovulation (with ovulation given as LH surge + 1 day). Data was obtained from 109?UK volunteers who provided daily urine samples, starting prior to conception and continuing through early pregnancy (collection done from 23/01/12 to 12/03/13, with the approval of the local ethics committee). Mean age of the volunteers was 29.50?years (SD 4.27, median 29 years, range 21–40). hCG was measured using the AutoDELFIA immunoassay system (Perkin Elmer).

Studies reporting a wide variability in hCG concentrations in early pregnancy have generally calculated pregnancy duration from the day of the last menstrual period (LMP). The variability of hCG concentrations in these studies is unsurprising, given the considerable intra- and inter-individual variation in the length of the follicular phase. In addition, inaccuracies frequently occur due to women's poor recollection of their LMP. Studies found that only 32 % of women had regular monthly cycles and were certain of their LMP date; a higher incidence of round number preferences was also recorded when women were asked the day of their LMP, with the 15th of the month given 2.5 times more often than expected. Early pregnancy bleeding, recent hormonal contraceptive use, or breastfeeding are all additional reasons why a woman may not have a reliable LMP date. When hCG concentrations are calculated based on the surge in luteinizing hormone that stimulates ovulation (LH surge), most of this variability disappears.?Fig. 2?shows the influence of an imperfect referencing method (LMP) on the precision of the urinary hCG nomogram for early pregnancy. This means that semi-quantitative hCG measurement in urine can be useful for determining the true gestational age or, if the time of conception is known, hCG measurement can contribute to the early detection of pregnancy disturbances.

Fig. 2: Impact of reference method used to determine pregnancy duration (day of pregnancy calculated from LMP (? 14 days) or from ovulation (LH surge + 1 day) on variability of urinary hCG in early pregnancy normograms by day. Median hCG levels overlay by day; variability was markedly increased when pregnancy duration was calculated from LMP as opposed to ovulation. The grey area is the 10th to 90th centile band for the US Gestational Age Study.

Below is a guideline to hCG levels in weeks during pregnancy

* These numbers are just a?guideline?– every woman’s level of hCG can rise differently. It is not necessarily the level that matters, but rather the change in the level.

Note:

Reference site?1：

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4119102/