I know of no medical announcement associated with the degree of emotional anticipation and anguish as that associated with a pending diagnosis/confirmation of pregnancy following infertility treatment. In fact, hardly a day goes by where I am not confronted by a patient anxiously seeking interpretation of a pregnancy test result.
Testing urine or blood for the presence of human chorionic gonadotropin (hCG) is the most effective and reliable way to confirm conception. The former, is far less expensive than the latter and is the most common method used. It is also more convenient because it can be performed in the convenience of the home setting. However, urine hCG testing for pregnancy is not nearly as reliable or as sensitive e as is blood hCG testing. Blood testing can detect implantation several days earlier than can a urine test. Modern pregnancy urine test kits can detect hCG about 16-18 days following ovulation (or 2-3 days after having missed a menstrual period), while blood tests can detect hCG, 12-13 days post-ovulation (i.e. even prior to menstruation).
The ability to detect hCG in the blood as early as possible and thereupon to track its increase, is particularly valuable in women undergoing controlled ovarian stimulation (COS) with or without intrauterine insemination (IUI) or after IVF. The earlier hCG can be detected in the blood and its concentration measured, the sooner levels can be tracked serially over time and so provide valuable information about the effectiveness of implantation, and the potential viability of the developing conceptus.
There are a few important points that should be considered when it comes to measuring interpreting blood hCG levels. These include the following:
- All modern day blood (and urine) hCG tests are highly specific in that they measure exclusively for hCG. There is in fact no cross-reactivity with other hormones such as estrogen, progesterone or LH.
- Post conception hCG levels, measured 10 days post ovulation or egg retrieval can vary widely (ranging from 5mIU/ml to above 400mIU/ml. The level will double every 48–72 hours up to the 6th week of gestation whereupon the doubling rate starts to slow down to about 96 hours. An hCG level of 13,000-290, 0000 mIU/ml is reached by the end of the 1st trimester (12 weeks) whereupon it slowly declines to approximately 26,000– 300,000 mIU/ml by full term. Below are the average hCG levels during the first trimester:
- 3 weeks LMP: 5 – 50 mIU/ml
- 4 weeks LMP: 5 – 426 mIU/ml
- 5 weeks LMP: 18 – 7,340 mIU/ml
- 6 weeks LMP: 1,080 – 56,500 mIU/ml
- 7 – 8 weeks LMP: 7, 650 – 229,000 mIU/ml
- 9 – 12 weeks LMP: 25,700 – 288,000 mIU/ml
- A single hCG blood level is not sufficient to assess the viability of an implanting embryo. Caution should be used in making too much of an initial hCG level. This is because a normal pregnancy can start with relatively low hCG blood levels. It is the rate of the rise of the blood hCG level that is relevant.
- In some cases the initially hCG level is within the normal range, but then fails to double in the ensuing 48-72hours. In some cases it might even plateau or decline, only to start doubling appropriately thereafter. When this happens, it could be due to:
- A recovering implantation, destined to develop into a clinical gestation
- A failing implantation (a chemical pregnancy)
- A multiple pregnancy which is spontaneously reducing (i.e., one or more of the concepti is being lost) or,
- An ectopic pregnancy which will either absorb spontaneously (a chemical-tubal gestation), or evolve into a full blown tubal pregnancy continue and declare itself through characteristic symptoms and signs of an intraperitoneal bleed.
- The blood hCG test needs to be repeated at least once after 48h and in some cases it will need to be repeated one or more times (at 48h intervals) thereafter, to confirm that implantation is progressing normally.
- Ultimately the diagnosis of a viable pregnancy requires confirmation of the presence of an intrauterine gestational sac by ultrasound examination. The earliest that this can be achieved is when the beta hCG level exceeds 1,000mIU/ml (i.e., around 5-6 weeks).
- Most physicians prefer to defer the performance of a routine US diagnosis of pregnancy until closer to the 7th week. This is because by that time, cardiac activity should be clearly detectable, allowing for more reliable assessment of pregnancy viability.
- There are cases where the blood beta hCG level is extraordinarily high or the rate of rise is well above the normal doubling rate. The commonest explanation is that more than one pregnancy has implanted. However in some cases it can point to a molar pregnancy
- Finally, there on rare occasions, conditions unrelated to pregnancy can result in detectable hCG levels in blood and urine. They include ovarian tumors that produce hCG, such as certain types of cystic teratomas (dermoid cysts) and some ovarian cancers such as dysgerminomas.