You have struggled to conceive. Now, finally, after doing IVF, you are pregnant and your beta hCG levels are positive. But are they good enough? What qualifies as a “good” beta number? Is a beta of 20 an indicator of a viable pregnancy? What about 15? The short answer: it depends. While beta hCG levels are useful indicators of fetal development and viability when measured during the first few weeks of pregnancy, there is no single measurement that will give you a definite answer. Beta levels are highly variable, and what is considered “acceptable” depends on a number of other factors.
Two criteria are particularly important at this point: the first is the beta hCG level measured on day 10 after a day 5 embryo transfer. The second is the rate of increase – usually measured by doubling time (DT). Pregnancies with an initial hCG value below 50 IU/L are at particularly high risk for miscarrying or being an ectopic pregnancy1. While some of these levels ultimately catch-up, your physician will most likely follow you closely by measuring your serial beta levels every 2 days. The DT is calculated by plotting multiple levels in the y axis, drawing a line between those points, and determining the number of days it takes for the level to double in the x axis. The overall DT is shorter overall in pregnancies and a range of 1.2 to 3.2 days is considered acceptable1. Because of the wide range, evaluating a pregnancy using multiple beta hCG tests several days apart is more predictive of the viability.
Unfortunately, it is difficult to feel safe until we see a fetal heartbeat around 6.5 weeks. At that stage, the risk of a miscarriage is less than 5% in most cases. Please note that physicians measure the number of weeks differently than do most patients. The 6.5 week mark is around 25 days after a day 5 ET. Unlike natural pregnancies where a progesterone level >25 is reassuring, IVF pregnancies are routinely supported with progesterone supplementation. If the progesterone is administered intramuscularly, measuring those levels is not helpful because one would only be measuring the adequacy of the injections, not fetal viability. Because vaginal progesterone does not affect serum progesterone levels, this test can still be used as additional reassurance in those using this type of progesterone supplementation.
- Bjercke S, Tanbo T, Dale PO, Mørkrid L, Abyholm T. Human chorionic gonadotrophin
concentrations in early pregnancy after in-vitro fertilization. Hum Reprod 1999;14:1642–6.
- Doubling time of urine hCG following ART. Fertil Steril 2005.