Urinary hCG patterns during the week following
P.A. Nepomnaschy1,3, C.R. Weinberg2, A.J. Wilcox1and D.D. Baird1
1Epidemiology Branch, National Institute of Environmental Health Sciences, National Institutes of Health, Department of Health and
HumanServices, PO BOX 12233,MD A3-05, Rm 309, 111 TW Alexander Drive, Research Triangle Park, NC, USA;2Biostatistics Branch,
National Institute of Environmental Health Sciences, National Institutes of Health, Department of Health and Human Services, Research
Triangle Park, NC, USA
3Correspondence address. E-mail: email@example.com
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 5 2.7–3.4). The relative rate of rise decreased
thereafter, reaching 1.6-fold (95% CI 5 1.5–1.8) between days 6 and 7. HCG levels followed a log-quadratic trajec-
tory, 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 pregnan-
cies. Later implantation may reflect characteristics of the uterus or conceptus that slow hCG production.
Keywords: pregnancy; hCG; spontaneous abortion; twins; fetal sex
The growth and development of the human embryo are
unobservable during the crucial early stages after implantation.
The best information on early growth comes indirectly, through
the measurement of hCG (human chorionic gonadotrophin)
produced by the trophoblastic cells of the conceptus. HCG is
a robust hormone, measurable in maternal serum and urine.
have been reported to be associated with the embryo’s genetic
quality, site of implantation (intrauterine or ectopic) and
developmental pace (Marshall et al., 1968; Kadar et al., 1981;
Check et al., 1992; Ho et al., 1997; Urbancsek et al., 2002;
Barnhart et al., 2004; Seeber et al., 2006). Consequently,
there is an interest in hCG as a biomarker of embryonic
health and a tool to evaluate the effects of endogenous and
exogenous challenges on very early gestation (Lohstroh et al.,
2007). First, however, it is necessary to describe the normal
longitudinal daily excretion patterns of hCG and its natural
variation among individuals.
HCG is an oligosaccharide glycoprotein hormone critical for
crine, autocrine, paracrine and endocrine actions that play vital
roles in the communication between conceptus and mother
during early gestation (Yang et al., 2003). HCG’s decisive
early roles include the ‘rescue’ of the corpus luteum (Zeleznik
and Pohl, 2006) and formation of the placental syncytium
gesterone production (Liu et al., 1995; Baird et al., 2003) are
crucial in supporting pregnancy until the placenta can produce
adequate levels of progesterone (Csapo and Pulkkinen, 1978).
Though the mRNA for the hCG subunits has been
detected as early as the 6–8-cell stage (Bonduelle et al.,
1988), the intact protein first becomes detectable in the
mother’s blood and urine between 6 and 14 days after fertiliza-
tion (Hay and Lopata, 1988; Wilcox et al., 1999; Lohstroh
et al., 2006). Most research on longitudinal urinary excretion
patterns of hCG has been conducted later in pregnancy [6 or
more weeks after the last menstrual period (LMP)] (Braunstein
et al., 1976; Gerhard and Runnebaum, 1984; Williams et al.,
1995; Gol et al., 2005). Profiles for earlier gestational intervals
have not been adequately characterized. This is particularly
true for the first week post-implantation, which coincides with
the onset of the placentation process (Malassine and Cronier,
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Human Reproduction Vol.23, No.2 pp. 271–277, 2008
Advance Access publication on December 14, 2007
Many past studies of very early hCG excretion have been
based on clinical populations and involve women undergoing
assisted fertility treatments (AFT), which limits their general-
izability. Reproductive profiles of clinical patients may be
inherently different from those of women in the general popu-
lation, and could be affected by the exogenous drugs (or related
stress) that accompany treatment (Batzer et al., 1981; Lam
et al., 1999; Cwikel et al., 2004). Additionally, many previous
studies are based on cross-sectional designs, with each woman
contributing only1–3 data points (Lambers et al.,2006; Seeber
et al., 2006). Such cross-sectional designs are inadequate for
exploring the among-women variations in hCG excretion.
Our objective is to provide a description of daily urinary
excretion of hCG during the first week after the estimated
onset of implantation, using a sample of naturally conceived
pregnancies in women with no known fertility problems. We
have previously focused on pregnancies resulting in early spon-
taneous abortion (before 6 weeks LMP) (Wilcox et al., 1999;
Baird et al., 2003). Here, we evaluate daily concentrations in
first-morning urinary hCG from clinical pregnancies (i.e.
those that survived at least 6 weeks LMP), and investigate
the extent to which fetal number, fetal viability or fetal sex
might affect the pattern of hCG rise.
Analyses were based on data collected in the context of the North
Carolina Early Pregnancy Study (NCEPS), which had as its original
objective to determine the incidence of early, sub-clinical, spon-
taneous abortion (before 6 weeks LMP). The field portion of the
study was carried out between 1982 and 1986. A total of 221
women, who were planning to conceive, were enrolled at the onset
of their attempt. Eligibility for participation required that women
had no known chronic health or fertility problems, and were not
under any hormone treatment. Participants’ ages ranged from 21 to
42 years (mean ¼ 30); most were white and college-educated
(Wilcox et al., 1988). All participants provided informed consent.
This research was approved by the Institutional Review Board of
the National Institute of Environmental Health Sciences.
Participants kept daily dairies in which they recorded menstrual bleed-
ing and symptoms of pregnancy. Women collected first morning urine
samples daily in 30 ml wide-mouth polypropylene jars with screw
tops. The collection of samples continued 8 weeks into the pregnancy
or for up to 6 months if no clinical pregnancy was identified. Samples
were stored in the participants’ home freezers (without preservatives),
with weekly retrieval and transport to a central storage unit where they
were kept at 2208C. Urine specimens were then packed in dry ice and
shipped by overnight freight to Columbia University for hCG assay
(Wilcox et al., 1985, 1988).
Hormonal assays and reproductive parameters
HCG assays were conducted from 1983 to 1987, within 6–24 months
after the end of each woman’s participation. HCG assays were carried
out in triplicate, using an immunoradiometric assay (Sepharose-IRMA
B101-R525) (Wilcox et al., 1988). Laboratory personnel were blind to
the outcomes of the clinical pregnancy. The specific primary target of
the IRMA was intact hCG, with cross-reactivity to bhCG (?70%)
(McChesney et al., 2005). The detection limit was 0.01 ng/ml
(Armstrong et al., 1984). Converting to bioassay units of purified
reference preparations, 1 ng in the IRMA is approximately equivalent
to 0.013 IU. Within-assayvariability in pooled samples was 21%;with
this removed, the variability among assays was 15% (Wilcox et al.,
1988). All specimens for a given woman were measured in the
same assay batch, except that additional dilutions were carried out
if necessary for high concentrations of hCG. The stability of intact
hCG was assessed by subjecting purified analytes in urine to 40
cycles of freezing and thawing and to storage at 48C for 4 weeks.
No loss of immunodetection for intact hCG analytes was evident
during the freeze–thaw process or at any time during that storage
period (McChesney et al., 2005).
Specimens were also analysed for steroid metabolites in duplicate,
using radioimmunoassay to determine urinary concentrations of
estrone-3-glucuronide (E1G) and pregnanediol-3-glucuronide (PdG)
(Wright et al., 1978; Samarajeewa et al., 1979).
Concentrations of intact hCG are similar in urine and serum
(Wehmann and Nisula 1981; Norman et al., 1987; McChesney
et al., 2005). Urine collection is non-invasive, which is an advantage
for studies requiring frequent specimen collection and non-clinical
settings. Creatinine concentrations were measured for a subset of
urine samples. Variations in urine concentration of creatinine were
trivial in relation to the steep daily rise of hCG (McChesney et al.,
2005). Accordingly, no adjustments for creatinine were performed
in the present analysis.
Definitions and reproductive end-points
Hormonal patterns were used to estimate ovulation and the onset of
implantation. The day of ovulation was inferred from the rapid
decline of the ratio of E1G to PdG (Baird et al., 1995; Baird et al.,
1991), which marks the luteinization of the ovarian follicle. This esti-
mator of ovulation has been validated by Ecochard et al. (2001), who
used ultrasound of the rupturing follicle to demonstrate that the
urinary steroid hormone ratio is as good a marker of ovulation as
the LH surge, and better than the LH peak.
Conception was inferred when the urinary concentration of hCG
exceeded 0.025 ng/ml for 3 consecutive days (Wilcox et al., 1988).
For each conception, the onset of implantation was approximated as
the first day of sustained production of urinary hCG above
0.015 ng/ml (Wilcox et al., 1999). Although hCG is reliably detected
in maternal urine only 6 or more days after fertilization (Wilcox et al.,
1999; Lohstroh et al., 2006), the conceptus probably begins secreting
hCG earlier (Bonduelle et al., 1988; Hay and Lopata, 1988). The
specific phase of the implantation process in which hCG reaches
maternal circulation and is excreted in urine is unknown (Chang
et al., 1998).
Of the 199 conceptions chemically detected in our study, 151 survived
at least 6 weeks after LMP (‘clinical pregnancy’). The initiation of
implantation was identified for 142 of the 151 pregnancies. In one
of the 142 pregnancies, a urine sample was missing near the onset
of hCG rise. We inferred that this was the likely day of implantation,
based on the fact that there was no detectable hCG on the previous
day, and by the subsequent day hCG was already more than 2-fold
higher than any confirmed day of first detection in our sample. Critical
hCG information was missing for the nine remaining pregnancies, and
these were excluded from further analysis. Of the 142 pregnancies in
which implantation could be identified, 121 ended in singleton births,
6in twinbirths,13 inspontaneous abortions,1in anectopic pregnancy
and 1 in a molar pregnancy (all identified by participants’ self-report).
Nepomnaschy et al.
Hormonal values were log-transformed for analysis in order to
normalize distributions and reduce the influence of outliers. Urinary
hCG excretion trajectories were evaluated using mixed model ana-
lyses (Proc Mixed in SAS 9.1; SAS Institute, Cary, NC, USA) with
a random-effect term to account for correlations among observations
within women. Comparisons of hCG trajectories among pregnancies
according to their outcomes, sex of the fetus and time to implantation
were performed by including the characteristic in question as a predic-
tor in the mixed model. The fit of competing models was assessed by
comparing the models’ restricted log-likelihoods using chi-squared
hCG trajectory during the first week following detection
During the first week following detection, average maternal
urinary concentration of hCG increased rapidly and continu-
ously (Tables I and II and Fig. 1). The overall pattern of
hCG excretion (Fig. 1) was well described by the following
lnhCG ¼ b0þ b1? time þ b2? time2
in which time is day in relation to hCG detection (day of hCG
detection ¼ 0), b0¼22.837 (SE ¼ 0.065), b1¼ 1.070 (SE ¼
0.031), b2¼20.046 (SE ¼ 0.005); P-values ,0.0001 for all
terms. The rate of increase in hCG excretion was steepest
between the first day of hCG detection and the following
day. The rate of increase progressively slowed in subsequent
days (Table II).
Variability among pregnancies
Individual hCG profiles varied markedly. We illustrate this
variability in five selected individual profiles of surviving preg-
nancies (Fig. 2). Some individual profiles follow a pattern
similar to the mean model (e.g. Fig. 2(A)), whereas others
diverge from it in various ways (e.g. Fig. 2(B–D)). There are
pregnancies, e.g. in which the rate of increase remains rela-
tively constant (e.g. Fig. 2(E)). In other pregnancies, hCG
rates of increase slow down for a few days (e.g. Fig. 2(B–
D)) and then increase abruptly and, in some cases, decrease
again afterwards (e.g. Fig. 2(B) and (D)). Abrupt increases
appeared to be more common towards the beginning of the
week and decelerations were more common towards the end.
hCG excretion and pregnancy survivability
The trajectory of hCG rise in the first week was not different for
spontaneous abortions and live births (P ¼ 0.80). Pregnancies
ending in spontaneous abortion presented as much variability
in their hCG trajectories as did surviving singleton pregnancies
(Levene’s test for homogeneity, P ¼ 0.61) (Fig. 3). Further-
more, among these clinical pregnancies, the mean time to
implantation was identical (9.15 days after estimated ovu-
lation) between surviving pregnancies and those resulting in
hCG excretion in twin pregnancies
Our sample included six sets of twins, all monozygotic. Zygos-
ity was assessed several years after birth using a validated set of
Table I. Daily geometric mean hCG concentrations in first morning urine
during the first week following detection calculated for 142 clinical
n Geometric mean (ng/ml)95% CI
aDay 1 ¼ day of detection (hCG . 0.015 ng/ml).
Table II. Daily rates of increase in urinary excretion of hCG during the first
week following detection for 142 clinical pregnancies.
n Rates of increaseb95% CI 10 percentile Median 90 percentile
aDay 1 ¼ day of detection (hCG . 0.015 ng/ml).
bThe rate of increase was calculated by exponentiating the means of daily
differences [ln hCGday22 ln hCGday1]. A value of 3.0 reflects a 3-fold
increase and a value of ,1 reflects a decline in hCG levels from one day to
Figure 1: Predicted hCG excretion pattern and observed values
during the first week of detection for 142 clinical pregnancies
Circles represent individual data points, the central solid line rep-
resents the hCG trajectory predicted by the regression equation and
the broken lines represent the 95% probability band for the model.
Day 1 ¼ day of detection (hCG . 0.015 ng/ml)
Urinary hCG patterns following implantation
questions answered by the mother. A visual inspection of hCG
trajectories for the twin pregnancies shows considerable vari-
ation, with an average trajectory very similar to that for survi-
ving singletons (Fig. 4).
hCG excretion and sex of the fetus
Sex of the fetus (65 boys and 56 girls) was not a significant pre-
dictor of urinary hCG levels (P ¼ 0.09) among pregnancies
resulting in surviving singletons (Fig. 5).
Time to implantation and hCG excretion trajectories
As we previously reported for these data (Wilcox et al.,1999),
the time between estimated day of ovulation and estimated day
of implantation ranged from 6 to 12 days (mean ¼ 9.1, SD ¼
1.12, median ¼ 9). The time it takes for a conceptus to
implant may reflect quality of the conceptus or the uterus. In
our sample of clinical pregnancies, time to implantation
emerged as a significant predictor of the pattern of hCG rise
(P , .0001). As shown in Fig. 6, conceptuses that implanted
early (7 days after ovulation or earlier) tended to have lower
hCG levels on the day of implantation but higher rates of
increase during the first week, compared with conceptuses
that implanted late (11 days or later). By the end of the first
week following hCG detection, late implanters showed lower
mean levels of hCG.
We evaluated maternal hCG urinary excretion patterns during
the first week following detection in 142 naturally conceived
clinical pregnancies. Daily mean urinary hCG concentrations
rose rapidly, with daily increases ranging from an initial
3-fold rise to a 1.6-fold rise by the end of the week. In contrast
with the smooth increase in the overall mean, individual
hCG trajectories were highly variable. Sharp increases were
Figure 4: Urinary hCG excretion profiles for six sets of monozygotic
twins during the first week of detection
The central solid line represents the hCG trajectory predicted by the
regression equation for 121 surviving singleton pregnancies and the
gray area represents the 95% confidence interval. Icons and associated
lines represent the 6 individual trajectories. Day 1 ¼ day of detection
(hCG . 0.015 ng/ml)
Figure 2: Selected set of five individual hCG urinary excretion trajec-
tories (labelled A–E) to illustrate between-pregnancy variability
The central solid line represents the hCG trajectory predicted by the
regression equation for 142 clinical pregnancies. Icons and associated
lines represent the five individual trajectories. Day 1 ¼ day of detec-
tion (hCG . 0.015 ng/ml)
Figure 3: Urinary hCG excretion profiles for 13 clinical spontaneous
abortions during the first week following implantation. Numbers
represent the length of gestation (from ovulation to bleeding)
The smoothcentral solidlinerepresents the hCG trajectorypredicted by
theregressionequationfor 121survivingsingletonspregnancies andthe
grayarearepresentsthe 95% confidence interval.Day 1 ¼ day ofdetec-
tion (hCG . 0.015 ng/ml)
Nepomnaschy et al.
sometimes interspersed with relative plateaus (Fig. 2). Some of
this may be measurement error, although the use of triplicate
assays reduces such error. The observed variation may also
reflect day-to-day changes in the trophoblastic invasion
process, as hCG-producing cells are brought in proximity to
the maternal blood supply. Alternatively, there could be vari-
able sequestering of hCG in maternal tissues prior to excretion.
Our sample was ethnically and socioeconomically homo-
geneous; a more diverse sample could possibly show even
higher heterogeneity in early hCG profiles.
Comparing our findings with those of previous studies is
complicated by differences in design, sensitivity of the hCG
assay used and data analysis methods. A study based on 25
pregnancies achieved via artificial insemination reports
higher average hCG values for the first 5 days following detec-
tion than the values we observed for the same period (Ho et al.,
1997). The differences in results can be at least partially
explained by the higher sensitivity of our assay which
allowed earlier pregnancy detections. Two prior studies that
examined longitudinal hCG rise patterns at the very earliest
time of pregnancy for naturally conceived pregnancies were
based on very small samples (Lenton and Woodward, 1988;
Lohstroh et al., 2006). Lohstroh et al. (2006) reported hCG
data from 13 naturally conceived clinical pregnancies for
days 10–14 from the FSH peak. The daily absolute increases
they observed are similar to ours. Lenton et al. (1982, 1988)
report data from 18 spontaneously conceived pregnancies.
They observed a deceleration, in the day-to-day relative rate
of increase during the first 12 days following implantation,
i.e. consistent with the pattern we describe. A recent review
of nine studies by Chung et al. (2006) provides evidence
suggesting that the deceleration in the relative rate of increase
of hCG levels continues after the first week post-implantation.
The time at which the relative rate of hCG rise starts to slow
down as pregnancy advances has long been a topic of debate
(Fritz and Guo, 1987). Studies discussing this issue focus on
different intervals within the first trimester and data from the
earliest stages of pregnancy are rarely well represented.
Some of these previous studies show an early deceleration
pattern (Lenton et al., 1982; Pittaway and Wentz, 1985;
Daya, 1987; Fritz and Guo, 1987; Check et al., 1992),
whereas others report a constant exponential rise (Kadar
et al., 1981; Zegers-Hochschild et al., 1994; Barnhart et al.,
Early hCG levels are regarded as a predictor of pregnancy
outcome (Check et al., 1992; France et al., 1996; Ho et al.,
1997; Yaron et al., 2002; Hauzman et al., 2004; Lohstroh
et al., 2007). While this is clearly true for very early losses
(before 6 weeks) (Baird et al., 2003; Lohstroh et al., 2006;
Wilcox et al., 1999), early hCG levels are a poor predictor of
clinical spontaneous abortions. In our data, conditional on sur-
vival to 6 weeks, the urinary hCG trajectory during the first
week had no association with spontaneous abortion. This
observation is consistent with results reported by Lohstroh
et al. (2005), who found no association between hCG levels
on day of detection and pregnancy outcome either in 62
fertile women undergoing artificial insemination or in 10 natu-
rally conceived pregnancies (Lohstroh et al., 2006). There is
some evidence, however, that differences in hCG slopes may
emerge during the second week, but findings are based on rela-
tively small samples or IVF patients (Lohstroh et al., 2006,
Figure 5: Daily hCG geometric means (GM) for surviving male and
female fetuses during the first week of hCG detection
Icons represent daily GMs and bars are drawn to plus/minus one stan-
dard error. Day 1 ¼ day of detection (hCG . 0.015 ng/ml)
Figure 6: Daily hCG trajectories by time elapsed between ovulation
and first hCG detection (i.e. time to implantation) for 142 clinical
pregnancies during the first week of detection
Lines represent the trajectories predicted by the regression model for
each day for each time to implantation category. The icons associated
with each line represent the observed daily geometric means for each
category. Day 0 ¼ estimated day of ovulation
Urinary hCG patterns following implantation
2007; Porat et al., 2007). Also, variations in hCG bioactivity
and hyperglycosylated hCG levels, which we did not
measure, may prove to be useful in assessing pregnancy viabi-
lity during the peri-implantation period (Ho et al., 1997; Loh-
stroh et al., 2006; Kovalevskaya et al., 2007).
The number of developing embryos has been proposed to
affect the trajectory of hCG (Zegers-Hochschild et al., 1994;
Hauzman et al., 2001; Urbancsek et al., 2002; Chung et al.,
2006). Some studies which focused on the earliest gestational
stages have, however, failed to observe an effect (Kelly
et al., 1991; Check et al., 1992). During the week following
the estimated day of implantation we found no differences in
either absolute hCG values or rates of rise between the twins
and singleton pregnancies.
By the second trimester, women bearing female fetuses have
higher hCG levels on average than those carrying males (Brody
and Carlstroem, 1965; Santolaya-Forgas et al., 1997; Spencer
2000). Yaron et al. (2001, 2002) report sex differences in
hCG levels by the third week post-fertilization, but others
have failed to observe differences that early in gestation
(Braunstein et al., 1980; Kletzky et al., 1985; Gol et al.,
2005). We found no sex-related differences in hCG levels
among surviving pregnancies during the first week of detec-
tion, suggesting that sex differences arise later.
Delay in implantation is a strong predictor of early preg-
nancy loss (before 6 weeks) (Wilcox et al., 1999). Here, we
report that, among pregnancies surviving at least 6 weeks,
those that implanted after luteal day 10 had a slower hCG
rise. The finding of a slower hCG rise might seem to support
the hypothesis that time to implantation is related to embryo
quality (Bolton et al., 1989; Woodward and Lenton 1992;
Rogers 1995). Both late implantation and a slower hCG rise
may reflect a slower growing conceptus (Liu et al., 1995;
Wilcox et al., 1999). However, conditional on survival to
6 weeks, neither late implantation nor a slower rate of
hCG rise during the first week were associated with survival
in our data.
In summary, maternal urinary hCG levels are quite variable
during the first week following implantation. During this gesta-
tional stage, hCG patterns rise very rapidly but the relative rate
of rise decelerates as the week advances. Among the factors
evaluated, the only significant predictor of hCG trajectories
during the first week was time to implantation.
We thank Drs Shyamal Peddada and Grace Kissling for statistical
advice, Dr Robert McConnaughey for assistance with data manage-
ment and Sue Edelstein and Brian Mills for assistance in composing
the final figures. Joy Pierce managed the field study and collection
of urine. Drs Olga Basso, Freya Kamel and Nicole Berry provided
comments on an earlier draft of the manuscript.
This research was supported by the Intramural Research
Program of the NIH, National Institute of Environmental
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