There were 58 enrolled patients. Two patients withdrew prior to completing the study leaving 56 completed cycles. Not all women provided samples at all time points. The mean patient age was 34.8 years with a range of 23–44 years. There were 6 Asians, 4 African Americans, 6 Hispanics and 40 Caucasians. A single patient received 5,000 IU of hCG for ovulation induction, another received 6,500 IU while all others were given 10,000 IU. The mean weight of the patients was 71.8 kg with a range of 46 kg–112 kg. Blastocyst transfer was performed in 70 % of cycles and earlier stage embryos transferred in 30 % of cases. The average number of embryos transferred was 1.3 with a range of 1–2. The overall clinical pregnancy rate was with 44 %. There was no significant difference between the pregnancy rate following blastocyst transfers (17 of 39, 44 %) versus earlier stage embryo transfer (8 of 17, 47 %). There were 12 singleton and 13 twin pregnancies. There were no triplets or higher order pregnancies. There were 6 biochemical pregnancies in the series, all of them following blastocyst transfer.
Figure and represent the kinetics of the rise in hhCG in serum for blastocyst and cleavage stage embryo transfers respectively during the first 12 days following blastocyst transfer. The Y axis is a log scale to accommodate the large increases in hhCG we observed during early pregnancy.
Fig. 1 Kinetics of Serum hhCG levels following embryo transfer. a: Blastocyst transfer. Diamonds = non-pregnant. Rectangles = Failed pregnancies. Circles = Clinical pregnancies. b Cleavage stage embryo transfer. Diamonds = non-pregnant. Circles = Clinical pregnancies (more ...)
On the day of transfer all but 2 patients had some measureable hhCG, presumably due to the cross-reactivity of the B152 antibody with the exogenously administered hCG. Ten thousand international units is equivalent to 1 g of hCG. With a one percent cross-reactivity of the B152 antibody with hCG, and our assay sensitivity of 4.5 pg/ml, the ability to detect residual hCG in these patients is well within expectation even if >99.9 % of the hCG were already eliminated. By day 6, serum and urine hhCG levels began to rise in clinical pregnancies whereas there was a decline in hhCG levels in non-pregnancies, presumably due to the metabolism of injected hCG for ovulation induction.
Table summarizes the performance of a single serum or urine hhCG value in detecting clinical pregnancies following IVF-ET at various times following ET. For cycles involving blastocyst transfer, a serum hhCG
75 pg/ml or a urine hhCG
25 pg/ml has a sensitivity and specificity of 100 % in diagnosing pregnancy. Even as early as day 4, a single serum hhCG value of
25 pg/ml had an 82 % sensitivity and 87 % specificity.
Sensitivities and specificities for pregnancy (both clinical and failed) for a single urine or blood hhCG level
Cycles involving cleavage stage embryo transfer are more variable. There were 2 ultimately clinical pregnancies with delayed hhCG rises until after 8 days. All other clinical pregnancies were detected at days 6 and 8.
As noted above, all patients had a low level of detectable hhCG on the day of transfer. In non-pregnancies, the level of hhCG decreased steadily thereafter. In clinical and biochemical pregnancies the hhCG levels did not fall during the initial 4 days post-ET, indicating probable synthesis of hhCG by the pre-implantation transferred embryos. By day 6, hhCG levels had risen appreciably above day 0 levels. By day 12 hhCG levels were approximately 100 fold higher than day zero levels.
Figure and demonstrate the kinetics of urine hhCG values during the post ET period. Although the curves show similar trends, the difference in urine hhCG values between clincal and biochemical pregnancies is not nearly as pronounced as for serum and urine hhCG values cannot discriminate between them.
Fig. 2 Kinetics of urine hhCG levels following embryo transfer. a Blastocyst transfer. Triangles = non-pregnant. Diamonds = Biochemical pregnancies. Circles = Clinical pregnancies. b Cleavage stage Embryo Transfer. Triangles: Non-pregnant. Circles: Clinical (more ...)
A commonly used calculation in monitoring early IVF-ET pregnancies is the approximate doubling of hCG levels every 48 h in the period beginning approximately 12 days following ET. We examined our data for the rate of increase for various 48 h time periods for both singleton and twin pregnancies. For the interval between day 4 and day 6, serum hhCG levels increased on average 18 fold in singleton pregnancies and 13 fold in twin pregnancies. The increases were 4 fold for singletons and 5 fold for twins in the interval of day 6 to day 8. Therefore the rate of rise of hhCG is not helpful in differentiating singleton from twin pregnancies. Of note, between days 6 and 8 hhCG rises much more steeply than the approximate doubling of hCG in the second week following ET.
There were 6 failed pregnancies in our series, all following blastocyst transfers. The hhCG levels are lower in biochemical pregnancies than in clinical pregnancies (Figs. and ). Table summarizes these data. A serum hhCG level of <300 pg/ml was able to identify all of the failed pregnancies at day 6 and a level of <6,000 pg/ml was able to identify all of the biochemical pregnancies at day 12 (see Table ). A single clnical pregnancy was below the cut-off value at day 6 and 2 pregnancies were below the cut-off value at day 12. It is important to note that all these data are for blastocyst transfers only. There were no cases of biochemical pregnancies for cleavage stage embryo transfers so no conclusions can be made. Urine hhCG levels did not discriminate between clinical and biochemical pregnancies.
Discrimination between clinical and failed pregnancies using serum hhCG for blastocyst transfers