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Serum hCG levels measured by time-resolved fluoroimmunoassay in first-trimester pregnancy and after pregnancy termination
Eur. J. Obstet. Gynecol. Reprod Biol., 26 (1987) 219-224
219
Elsevier I30
00541
Serum hCG levels measured by time-resolved fluoroimmunoassay in first-trimester pregnancy and after pregnancy termination J. M&men
I, L. Anttila *, K. Irjala 2, T. Salmi r and H.-L. Kaihola *
’ Department of Obstetrics and Gynecology, University Central Hospital of Turku, and 2 Central Laboratory, Turku University Hospiial, Finland
Accepted for publication 30 June 1987
Time-resolved fluoroinmumoassay (TR-FIA) reliably shows the concentrations of serum hCG during the first trimester of normal pregnancy. After first-trimester induced abortion the mean disappearance of hCG in serum (under 10 IU/l) takes place in three weeks. TR-FIA is a convenient and ultrarapid method for diagnosing pregnancy-related disorders. Pregnancy; Human chorionic gonadotropin; Abortion; Disappearance time; Daily fluctuation; TR-FIA
Introduction
Human chorionic gonadotropin (hCG) becomes detectable at a level of 2 IU/l in serum 8 days after conception [7]. After implantation serum hCG levels begin to rise rapidly. The exponential rise reaches a peak of about 100000 IU/l at the ninth week of gestation and is followed by a fall to 10000 IU/l by the 18th week, at which level it remains until the end of pregnancy [3]. Detectable levels of hCG in plasma have been observed up to 60 days after first-trimester induced abortion [8,9,11,15]. The long disappearance time must be kept in mind in women who are examined for gynecological conditions in the weeks after termination of an early pregnancy. Correspondence: Juha Miikinen MD, Department of Obstetrics and Gynecology, University Central Hospital of Turku, Kiinamyllynkatu 4-8, 20520 Turku 52, SF - Finland.
0028-2243/87/$03.50 0 1987 Elsevier Science Publishers B.V. (Biomedical Division)
220
Plasma hCG levels in early pregnancy are generally determined by radioimmunoassay (RIA) [2,7,15]. Since the method of fluoroimrnunometric assay for biological samples with time-resolved fluoroimmunoassay (TR-FIA) has been developed for clinical purposes [14], the determination of hCG has become more rapid and clinically more sensitive [12,16]. The rapidity of the assay is extremely valuable for clinical purposes in diagnosing gynecological emergencies, such as suspected cases of ectopic pregnancy. In the present study TR-FIA was carried out for clinical purposes. Our objective was to establish the hCG concentrations in the first trimester of normal pregnancy and to determine the time between the removal of all trophoblastic tissue and the disappearance of hCG from the blood after termination of first-trimester pregnancy. Material and methods
Seventy-seven determinations of hCG levels were obtained in 41 patients admitted to the hospital for pregnancy terminations. Patients were included only if the clinical evaluation of size of the uterus correlated with the time of amenorrhea. Any patients with suspected abnormal pregnancy (ovum abortivum, missed abortion, threatened or incipient abortion and twin or molar pregnancy) were excluded. Also patients who appeared to have macroscopically abnormal evacuation material obtained later in the termination procedure were excluded. The time of amenorrhea counted from the first day of the last reported menstrual period ranged from 6 to 18 weeks. All patients were physically healthy and aged between 15 and 43 years (mean age 25.3 years). Blood samples were drawn twice in 34, once in 6 and three times in one patient before abortion. The hCG disappearance time was studied after legal termination of first-trimester pregnancy in 35 patients. Normal serum creatinine levels were measured in all patients. The mean amenorrhea time before the induction of abortion was 67.4 days (range 53-96 days). Clinical evaluation of the size of the uterus correlated with the week of amenorrhea. Again, patients with suspicion of abnormal pregnancy were excluded from the series. All induced abortions were performed with vacuum suction curettage. Attention was paid to the material obtained during the procedure to exclude abnormal, especially molar, pregnancy. During the follow-up every patient used contraception. Initial blood samples in the patients were drawn on the day prior the termination of the pregnancy. The subsequent samples were obtained on three postoperative days (n = 18) in the hospital and then two (n = 26) and four (n = 23) weeks after the induced abortion. The daily fluctuation of the hCG level was examined in nine patients (mean age 22.8 years, mean amenorrhea 67 days); consecutive samples were drawn prior the operation at 8 and 12 o’clock in the morning. Serum hCG was measured by time-resolved fluoroimmunoassay [12]. This direct immunometric sandwich assay involves two monoclonal antibodies, one direct against the beta subunit and the other, an Eu-labelled antibody, against the alpha subunit of the hCG molecule. The first antibody is immobilized on the surface of the wells in a microtitration strip. For detection of the intensity of the fluorescence a long-decay Eu chelate is formed.
221
A commercial kit Delfia hCG, reference preparation 1st IPR (LKB-Wallac, Turku, Finland), was used according to the instructions of the manufacturer, although a shorter incubation time (15 min) was used and samples were diluted 1 : 5 or more, if needed, with normal male serum. With this modification the sensitivity of the assay is 10 IU/l. The interassay precision (CV) of the method was 6.1% at a concentration of 118 IU/l. The cross-reactivity of the method, according to the manufacturer, is less than 0.5% for LH. Student’s t-test was used for statistical purposes. Results
The individual values of the 77 hCG determinations in first-trimester pregnancy are shown in Fig. 1. The top values were clustered around the time between 57 and 70 days. The mean concentrations of hCG ( f SEM) at different amenorrhea times are seen in Fig. 2. The top values were observed again during the ninth week of amenorrhea. The baseline values of hCG before the curettage ranged between 20800 and 185 000 IU/l, with a mean of 63400 IU/l (SEM = 7 500 IU/l). After uterine evacuation hCG fell rapidly within two days (n = 16) to a mean concentration of 9600 IU/l (SEM = 1.300 IU/l). The decrease in hCG was observed in all cases. The disappearance curve of hCG (Fig. 3) reached a level of less than 10 IU/l hCG in 21 days (95% confidence limit of 15-32 days). When the initial level was 50000 IU/l hCG or more prior to the abortion (n = 16) this level was reached in 22 days (95% confidence limit 14-31 days) and with an initial level of less than 50000 IU/l hCG (n = 19) this level was reached in 20 days (15-28 days). At 8 o’clock in the morning, before the vacuum suction curettage, the mean concentration of hCG was 106 700 IU/l + 18 100 IU/l and 4 h later, at 12 o’clock,
hCG lull 1000000
+/+
100 10
I--010
30
r
I-
50
70
io uii0
’ ii0
DAYS Fig. 1. Individual serum hCG concentrations during normal first-trimester pregnancy. Semilogarithmic scale. The samples between 7 and 8, 9 and 10, and 11 and 12 weeks of amenorrhea are separated by vertical lines.
222
hCG
IUll
80000\ 60000/
50000-
\
LOOOO30000200007000010000-
/ 1lll1,I‘I 6 8 IO
12
IL
ItI 16
I 18weeks
Fig. 2. Serum hCG levels during normal first-trimester pregnancy by week of amenorrhea (mean * SEM).
0
10
20 DAYS
30
40
Fig. 3. The disappearance curve of serum hCG in women with induced abortion. Semilogarith’mic scale. The dotted lines indicate 95% confidence limits.
the mean concentration of hCG was statistically (p < 0.05).
significantly
lower, i.e. 98500
IU/l + 16 200 IU/l Discussion
The present study shows that the levels of hCG during the first trimester of pregnancy studied by TR-FIA are essentially similar to the levels measured by RIA [2,3]. This indicates that this novel ultrarapid method is useful for clinical emergencies, e.g. in suspected cases of ectopic pregnancy. The maximum concentrations of hCG were observed in the ninth week of amenorrhea as described earlier [3]. The mean concentration of 70000 IU/l of hCG in the current study is, however, somewhat higher than that of an earlier study [2]. The present elimination curve of hCG agrees with earlier findings showing that the disappearance curves fit a two-component model, the initial fast phase having a half-life of 5-9 h, followed by
223
a slower phase with a half-life of 22-32 h [5,10,13]. The disappearance time of hCG appears to be independent of the initial level of hCG (above and under 50000 IU/l hCG) before the termination procedure, as suggested earlier [9]. The fluctuations in the hCG level within 4 h before induction of abortion were studied in nine patients. There was a significant difference (p < 0.05) between these concentrations; higher levels were measured early in the morning. Despite the mathematical significance it is suggested that this finding is not of biological importance where such high levels of hCG concentrations are concerned. Possibly sleep or physical exercise, for example, contributed to the values. In abortive pregnancies hCG concentrations begin to fall away from the normal range within a very short time, even though frank abortions may not occur for days or even weeks [6,7]. In these days quantitative hCG measurements are routine and an individual value during a specific week of amenorrhea (Fig. 2) will help to differentiate gynecological emergencies from elective cases. This is especially true in patients at risk for ectopic pregnancy, in threatened abortion, multiple pregnancy or suspected trophoblastic disease, or when the estimate of the duration of amenorrhea is not reliable. Of course, ultrasonic measurements, serial samples and rate of increase of serum hCG are more useful in suspected cases of early failures of pregnancy, whenever these are available [l]. The time for elimination of hCG depends on the clinical status of the pregnancy at the time of termination, the individual clearance rate of hCG, the sensitivity of the method, and, of course, the completeness of initial tissue removal [15]. Although no routine ultrasound evaluations were performed, the current patients represent clinically normal first-trimester pregnancies. The pregnancy terminations were performed with vacuum suction curettage, which is known entail one of the longest elimination times of hCG as compared with other termination procedures [9,17]. Except for some uncontrollable venous seeding of trophoblastic cells [4,18], the factors which account for the variation in hCG clearance, including molar pregnancy, were eliminated in this study. Although the actual disappearance time will be somewhere in between the last elevated hCG value and the first value under 10 IU/l hCG, the natural disappearance of hCG after suction curettage will be observed within three weeks. Before and after that, patients who exceed the 95% confidence limit have to be followed up if there is suspicion of pregnancy-related disorders. Sensitive and specific radioimmunoassays (RIAs) for hCG have generally been used to describe the profiles of maternal hCG during early pregnancy for both theoretical and clinical purposes. A limit of detection of 2 IU/l for sensitivity of hCG has been used [9]. A cut-off level of 10 IU/l has been advocated in other studies [15,16]. This reference level is also very apt for studies with TR-FIA, since the laboratory time is still a very brief 20 min [16]. However, it is acknowledged that the sensitivity of various assays may be difficult to compare when different antibodies and different reference preparations are used. Detectable levels of hCG (10 IU/l or more) have been determined for up to 60 days after induced abortion [15], while the median disappearance of hCG has been reported to be 30-37 days [7-91. It is possible that in 27-33 days after induced abortion the hCG level is more than 10 IU/l due to a new pregnancy [7-91. This fact must be kept in mind to avoid clinical confusion. Also the new highly sensitive
224
‘home tests’ may also give failed positive results which in fact arise from subclinical abortion or ectopic pregnancy. With regard to these observations the current routine in quantitative TR-FIA studies is believed to give clinically useful information, especially in suspected cases of ectopic pregnancy. In conclusion, the TR-FIA technique shows the same trend in hCG levels during the first trimester of normal pregnancy as RIA. It also parallels RIA in determining the elimination of hCG after induced first-trimester abortion. In examinations for gynecological conditions after induced abortion, three weeks appears to be the mean disappearance time of hCG. TR-FIA is a rapid and reliable method which should be used in gynecological emergencies where there is suspicion of pregnancy-related disorders. References 1 Batzer FR, Weiner S, Corson SL, Schlaff S, Otis C. Landmarks during the first forty-two days of gestation demonstrated by the b-subunit of human chorionic gonadotropin and ultrasound. Am J Obstet Gynecol 1983;146:973-979. 2 Braunstein GD, Rasor J, Adler D, Danzer H, Wade ME Serum human chorionic gonadotropin levels throughout normal pregnancy. Am J Obstet Gynecol 1976;126:678-681. 3 Braunstein GD, Karow WG, Gentry WC, Rasor J, Wade ME. First trimester chorionic gonadotropin measurements as an aid in the diagnosis of early pregnancy disorders. Am J Obstet Gynecol 1978;131:25-32. 4 Douglas GW, Thomas L, Carr C, Cullen NM, Morris R. Trophoblast in the circulating blood during pregnancy. Am J Obstet Gynecol 1959;78:960-973. 5 Griishel-Stewart U. Die Placenta des Menschen. First edition. Edited by V Becker, TH Schiebler, F Kubli. Stuttgart: Georg Thieme Verlag, 1981:212-233. 6 Jovanovic L, Dawood MY, Landesman R, Saxena BB. Hormonal profile as a prognostic index of early threatened abortion. Am J Obstet Gynecol1978;130:274-278. 7 Lenton EA, Neal LM, Sulaiman R. Plasma concentration of human chorionic gonadotropin from the time of implantation until the second week of pregnancy. Fertil Steril 1982;37:773-778. 8 L&hteemn%ki P. The disappearance of hCG and return of pituitary function after abortion. Clin Endocrinol 1978;9:101-112. 9 Marrs RP, Kletzky OA, Howard WF, Mishell DR. Disappearance of human chorionic gonadotropin and resumption of ovulation following abortion. Am J Obstet Gynecoi 1979;135:731-736. 10 Midgley AR Jr, Jaffe RB. Regulation of human gonadotropins: II. Disappearance of human chorionic gonadotropin following delivery. J Clin Endocrinol1968;28:1712-1718. 11 Pastorfide GB, Goldstein DP, Kosasa TS, Levesque D. Serum chorionic gonadotropin activity after molar pregnancy, therapeutic abortion, and term delivery. Am J Obstet Gynecol 1974;118:293-294. 12 Pettersson K, Siitari H, Hemmill I, Soini E, Liivgren T, I-B-en V, Tanner P, Stenman U-H. Time resolved fluoroirnmunoassay of human choriogonadotropin. Clin Chem 1983;29:60-64. 13 Rizkallah T, Gurpide E, Vandewiele RL. Metabolism of HCG in man. J Clin Endocrinol 1969;29:92-100. 14 Soini E, Hemmiha I. Fluoroimmunoassay: present status and key problems. Clin Chem 1979;25:353-361. 15 Steier JA, Bergsjo P, Myking OL. Human chorionic gonadotropin in maternal plasma after induced abortion, spontaneous abortion, and removed ectopic pregnancy. Obstet Gynecol 1984;64:391-394. 16 Stemnan U-H, Alftan H, Myllynen L, Sepptig M. Ultrarapid and higbly sensitive time-resolved fhtoroimmunometric assay for chorionic gonadotropin, Lancet 1983;ii:647-649. I7 Vaitukaitis JL. Changing placental concentrations of human chorionic gonadotropin and its subunits during gestation. J Clin Endocrinol Metab 1974;38:755-760. 18 Wagner D. Trophoblastic cells in the blood stream in normal and abnormal pregnancy. Acta Cytol 1968:12:137-139.
219
Elsevier I30
00541
Serum hCG levels measured by time-resolved fluoroimmunoassay in first-trimester pregnancy and after pregnancy termination J. M&men
I, L. Anttila *, K. Irjala 2, T. Salmi r and H.-L. Kaihola *
’ Department of Obstetrics and Gynecology, University Central Hospital of Turku, and 2 Central Laboratory, Turku University Hospiial, Finland
Accepted for publication 30 June 1987
Time-resolved fluoroinmumoassay (TR-FIA) reliably shows the concentrations of serum hCG during the first trimester of normal pregnancy. After first-trimester induced abortion the mean disappearance of hCG in serum (under 10 IU/l) takes place in three weeks. TR-FIA is a convenient and ultrarapid method for diagnosing pregnancy-related disorders. Pregnancy; Human chorionic gonadotropin; Abortion; Disappearance time; Daily fluctuation; TR-FIA
Introduction
Human chorionic gonadotropin (hCG) becomes detectable at a level of 2 IU/l in serum 8 days after conception [7]. After implantation serum hCG levels begin to rise rapidly. The exponential rise reaches a peak of about 100000 IU/l at the ninth week of gestation and is followed by a fall to 10000 IU/l by the 18th week, at which level it remains until the end of pregnancy [3]. Detectable levels of hCG in plasma have been observed up to 60 days after first-trimester induced abortion [8,9,11,15]. The long disappearance time must be kept in mind in women who are examined for gynecological conditions in the weeks after termination of an early pregnancy. Correspondence: Juha Miikinen MD, Department of Obstetrics and Gynecology, University Central Hospital of Turku, Kiinamyllynkatu 4-8, 20520 Turku 52, SF - Finland.
0028-2243/87/$03.50 0 1987 Elsevier Science Publishers B.V. (Biomedical Division)
220
Plasma hCG levels in early pregnancy are generally determined by radioimmunoassay (RIA) [2,7,15]. Since the method of fluoroimrnunometric assay for biological samples with time-resolved fluoroimmunoassay (TR-FIA) has been developed for clinical purposes [14], the determination of hCG has become more rapid and clinically more sensitive [12,16]. The rapidity of the assay is extremely valuable for clinical purposes in diagnosing gynecological emergencies, such as suspected cases of ectopic pregnancy. In the present study TR-FIA was carried out for clinical purposes. Our objective was to establish the hCG concentrations in the first trimester of normal pregnancy and to determine the time between the removal of all trophoblastic tissue and the disappearance of hCG from the blood after termination of first-trimester pregnancy. Material and methods
Seventy-seven determinations of hCG levels were obtained in 41 patients admitted to the hospital for pregnancy terminations. Patients were included only if the clinical evaluation of size of the uterus correlated with the time of amenorrhea. Any patients with suspected abnormal pregnancy (ovum abortivum, missed abortion, threatened or incipient abortion and twin or molar pregnancy) were excluded. Also patients who appeared to have macroscopically abnormal evacuation material obtained later in the termination procedure were excluded. The time of amenorrhea counted from the first day of the last reported menstrual period ranged from 6 to 18 weeks. All patients were physically healthy and aged between 15 and 43 years (mean age 25.3 years). Blood samples were drawn twice in 34, once in 6 and three times in one patient before abortion. The hCG disappearance time was studied after legal termination of first-trimester pregnancy in 35 patients. Normal serum creatinine levels were measured in all patients. The mean amenorrhea time before the induction of abortion was 67.4 days (range 53-96 days). Clinical evaluation of the size of the uterus correlated with the week of amenorrhea. Again, patients with suspicion of abnormal pregnancy were excluded from the series. All induced abortions were performed with vacuum suction curettage. Attention was paid to the material obtained during the procedure to exclude abnormal, especially molar, pregnancy. During the follow-up every patient used contraception. Initial blood samples in the patients were drawn on the day prior the termination of the pregnancy. The subsequent samples were obtained on three postoperative days (n = 18) in the hospital and then two (n = 26) and four (n = 23) weeks after the induced abortion. The daily fluctuation of the hCG level was examined in nine patients (mean age 22.8 years, mean amenorrhea 67 days); consecutive samples were drawn prior the operation at 8 and 12 o’clock in the morning. Serum hCG was measured by time-resolved fluoroimmunoassay [12]. This direct immunometric sandwich assay involves two monoclonal antibodies, one direct against the beta subunit and the other, an Eu-labelled antibody, against the alpha subunit of the hCG molecule. The first antibody is immobilized on the surface of the wells in a microtitration strip. For detection of the intensity of the fluorescence a long-decay Eu chelate is formed.
221
A commercial kit Delfia hCG, reference preparation 1st IPR (LKB-Wallac, Turku, Finland), was used according to the instructions of the manufacturer, although a shorter incubation time (15 min) was used and samples were diluted 1 : 5 or more, if needed, with normal male serum. With this modification the sensitivity of the assay is 10 IU/l. The interassay precision (CV) of the method was 6.1% at a concentration of 118 IU/l. The cross-reactivity of the method, according to the manufacturer, is less than 0.5% for LH. Student’s t-test was used for statistical purposes. Results
The individual values of the 77 hCG determinations in first-trimester pregnancy are shown in Fig. 1. The top values were clustered around the time between 57 and 70 days. The mean concentrations of hCG ( f SEM) at different amenorrhea times are seen in Fig. 2. The top values were observed again during the ninth week of amenorrhea. The baseline values of hCG before the curettage ranged between 20800 and 185 000 IU/l, with a mean of 63400 IU/l (SEM = 7 500 IU/l). After uterine evacuation hCG fell rapidly within two days (n = 16) to a mean concentration of 9600 IU/l (SEM = 1.300 IU/l). The decrease in hCG was observed in all cases. The disappearance curve of hCG (Fig. 3) reached a level of less than 10 IU/l hCG in 21 days (95% confidence limit of 15-32 days). When the initial level was 50000 IU/l hCG or more prior to the abortion (n = 16) this level was reached in 22 days (95% confidence limit 14-31 days) and with an initial level of less than 50000 IU/l hCG (n = 19) this level was reached in 20 days (15-28 days). At 8 o’clock in the morning, before the vacuum suction curettage, the mean concentration of hCG was 106 700 IU/l + 18 100 IU/l and 4 h later, at 12 o’clock,
hCG lull 1000000
+/+
100 10
I--010
30
r
I-
50
70
io uii0
’ ii0
DAYS Fig. 1. Individual serum hCG concentrations during normal first-trimester pregnancy. Semilogarithmic scale. The samples between 7 and 8, 9 and 10, and 11 and 12 weeks of amenorrhea are separated by vertical lines.
222
hCG
IUll
80000\ 60000/
50000-
\
LOOOO30000200007000010000-
/ 1lll1,I‘I 6 8 IO
12
IL
ItI 16
I 18weeks
Fig. 2. Serum hCG levels during normal first-trimester pregnancy by week of amenorrhea (mean * SEM).
0
10
20 DAYS
30
40
Fig. 3. The disappearance curve of serum hCG in women with induced abortion. Semilogarith’mic scale. The dotted lines indicate 95% confidence limits.
the mean concentration of hCG was statistically (p < 0.05).
significantly
lower, i.e. 98500
IU/l + 16 200 IU/l Discussion
The present study shows that the levels of hCG during the first trimester of pregnancy studied by TR-FIA are essentially similar to the levels measured by RIA [2,3]. This indicates that this novel ultrarapid method is useful for clinical emergencies, e.g. in suspected cases of ectopic pregnancy. The maximum concentrations of hCG were observed in the ninth week of amenorrhea as described earlier [3]. The mean concentration of 70000 IU/l of hCG in the current study is, however, somewhat higher than that of an earlier study [2]. The present elimination curve of hCG agrees with earlier findings showing that the disappearance curves fit a two-component model, the initial fast phase having a half-life of 5-9 h, followed by
223
a slower phase with a half-life of 22-32 h [5,10,13]. The disappearance time of hCG appears to be independent of the initial level of hCG (above and under 50000 IU/l hCG) before the termination procedure, as suggested earlier [9]. The fluctuations in the hCG level within 4 h before induction of abortion were studied in nine patients. There was a significant difference (p < 0.05) between these concentrations; higher levels were measured early in the morning. Despite the mathematical significance it is suggested that this finding is not of biological importance where such high levels of hCG concentrations are concerned. Possibly sleep or physical exercise, for example, contributed to the values. In abortive pregnancies hCG concentrations begin to fall away from the normal range within a very short time, even though frank abortions may not occur for days or even weeks [6,7]. In these days quantitative hCG measurements are routine and an individual value during a specific week of amenorrhea (Fig. 2) will help to differentiate gynecological emergencies from elective cases. This is especially true in patients at risk for ectopic pregnancy, in threatened abortion, multiple pregnancy or suspected trophoblastic disease, or when the estimate of the duration of amenorrhea is not reliable. Of course, ultrasonic measurements, serial samples and rate of increase of serum hCG are more useful in suspected cases of early failures of pregnancy, whenever these are available [l]. The time for elimination of hCG depends on the clinical status of the pregnancy at the time of termination, the individual clearance rate of hCG, the sensitivity of the method, and, of course, the completeness of initial tissue removal [15]. Although no routine ultrasound evaluations were performed, the current patients represent clinically normal first-trimester pregnancies. The pregnancy terminations were performed with vacuum suction curettage, which is known entail one of the longest elimination times of hCG as compared with other termination procedures [9,17]. Except for some uncontrollable venous seeding of trophoblastic cells [4,18], the factors which account for the variation in hCG clearance, including molar pregnancy, were eliminated in this study. Although the actual disappearance time will be somewhere in between the last elevated hCG value and the first value under 10 IU/l hCG, the natural disappearance of hCG after suction curettage will be observed within three weeks. Before and after that, patients who exceed the 95% confidence limit have to be followed up if there is suspicion of pregnancy-related disorders. Sensitive and specific radioimmunoassays (RIAs) for hCG have generally been used to describe the profiles of maternal hCG during early pregnancy for both theoretical and clinical purposes. A limit of detection of 2 IU/l for sensitivity of hCG has been used [9]. A cut-off level of 10 IU/l has been advocated in other studies [15,16]. This reference level is also very apt for studies with TR-FIA, since the laboratory time is still a very brief 20 min [16]. However, it is acknowledged that the sensitivity of various assays may be difficult to compare when different antibodies and different reference preparations are used. Detectable levels of hCG (10 IU/l or more) have been determined for up to 60 days after induced abortion [15], while the median disappearance of hCG has been reported to be 30-37 days [7-91. It is possible that in 27-33 days after induced abortion the hCG level is more than 10 IU/l due to a new pregnancy [7-91. This fact must be kept in mind to avoid clinical confusion. Also the new highly sensitive
224
‘home tests’ may also give failed positive results which in fact arise from subclinical abortion or ectopic pregnancy. With regard to these observations the current routine in quantitative TR-FIA studies is believed to give clinically useful information, especially in suspected cases of ectopic pregnancy. In conclusion, the TR-FIA technique shows the same trend in hCG levels during the first trimester of normal pregnancy as RIA. It also parallels RIA in determining the elimination of hCG after induced first-trimester abortion. In examinations for gynecological conditions after induced abortion, three weeks appears to be the mean disappearance time of hCG. TR-FIA is a rapid and reliable method which should be used in gynecological emergencies where there is suspicion of pregnancy-related disorders. References 1 Batzer FR, Weiner S, Corson SL, Schlaff S, Otis C. Landmarks during the first forty-two days of gestation demonstrated by the b-subunit of human chorionic gonadotropin and ultrasound. Am J Obstet Gynecol 1983;146:973-979. 2 Braunstein GD, Rasor J, Adler D, Danzer H, Wade ME Serum human chorionic gonadotropin levels throughout normal pregnancy. Am J Obstet Gynecol 1976;126:678-681. 3 Braunstein GD, Karow WG, Gentry WC, Rasor J, Wade ME. First trimester chorionic gonadotropin measurements as an aid in the diagnosis of early pregnancy disorders. Am J Obstet Gynecol 1978;131:25-32. 4 Douglas GW, Thomas L, Carr C, Cullen NM, Morris R. Trophoblast in the circulating blood during pregnancy. Am J Obstet Gynecol 1959;78:960-973. 5 Griishel-Stewart U. Die Placenta des Menschen. First edition. Edited by V Becker, TH Schiebler, F Kubli. Stuttgart: Georg Thieme Verlag, 1981:212-233. 6 Jovanovic L, Dawood MY, Landesman R, Saxena BB. Hormonal profile as a prognostic index of early threatened abortion. Am J Obstet Gynecol1978;130:274-278. 7 Lenton EA, Neal LM, Sulaiman R. Plasma concentration of human chorionic gonadotropin from the time of implantation until the second week of pregnancy. Fertil Steril 1982;37:773-778. 8 L&hteemn%ki P. The disappearance of hCG and return of pituitary function after abortion. Clin Endocrinol 1978;9:101-112. 9 Marrs RP, Kletzky OA, Howard WF, Mishell DR. Disappearance of human chorionic gonadotropin and resumption of ovulation following abortion. Am J Obstet Gynecoi 1979;135:731-736. 10 Midgley AR Jr, Jaffe RB. Regulation of human gonadotropins: II. Disappearance of human chorionic gonadotropin following delivery. J Clin Endocrinol1968;28:1712-1718. 11 Pastorfide GB, Goldstein DP, Kosasa TS, Levesque D. Serum chorionic gonadotropin activity after molar pregnancy, therapeutic abortion, and term delivery. Am J Obstet Gynecol 1974;118:293-294. 12 Pettersson K, Siitari H, Hemmill I, Soini E, Liivgren T, I-B-en V, Tanner P, Stenman U-H. Time resolved fluoroirnmunoassay of human choriogonadotropin. Clin Chem 1983;29:60-64. 13 Rizkallah T, Gurpide E, Vandewiele RL. Metabolism of HCG in man. J Clin Endocrinol 1969;29:92-100. 14 Soini E, Hemmiha I. Fluoroimmunoassay: present status and key problems. Clin Chem 1979;25:353-361. 15 Steier JA, Bergsjo P, Myking OL. Human chorionic gonadotropin in maternal plasma after induced abortion, spontaneous abortion, and removed ectopic pregnancy. Obstet Gynecol 1984;64:391-394. 16 Stemnan U-H, Alftan H, Myllynen L, Sepptig M. Ultrarapid and higbly sensitive time-resolved fhtoroimmunometric assay for chorionic gonadotropin, Lancet 1983;ii:647-649. I7 Vaitukaitis JL. Changing placental concentrations of human chorionic gonadotropin and its subunits during gestation. J Clin Endocrinol Metab 1974;38:755-760. 18 Wagner D. Trophoblastic cells in the blood stream in normal and abnormal pregnancy. Acta Cytol 1968:12:137-139.