That first glimpse of two pink lines–can it be?–and your heart start to pound with excitement. You’re pregnant!
But after a few moments of celebration, you descend back to earth. Okay, you’re pregnant, but for how long? Will this pregnancy stick?
You have entered a new, more hopeful limbo than the much bemoaned two-week wait. But it’s still no picnic.
We all know that miscarriage is very common, especially early in pregnancy. And for most women, good info about viability does not come until the first ultrasound, usually performed at 8-10 weeks.
Undergoing fertility treatments is less fun than a hangover. But they have one silver lining: Once pregnant, you receive information about your chances of a healthy pregnancy much earlier, from your “betas”–blood tests of your beta hCG (Human Chorionic Gonadotropin) levels.
What is HCG (Human Chorionic Gonadotropin)?
Embryos produce hCG once they implant. This hCG then passes into mom’s bloodstream to help maintain the uterine lining and keep progesterone levels high, allowing the pregnancy to progress.
During the first trimester, blood levels of HCG rises quickly. They usually double every 48 hours, until reaching a peak around 20 weeks. After this peak, they begin a slow decline.
Predicting ongoing pregnancy with HCG
The level of hCG in your blood predicts your chances of an ongoing pregnancy–which researchers usually define as one that lasts through the first 8-12 weeks.
The table below summarizes findings from several IVF-based studies which tracked pregnancy outcomes by hCG levels.
Note: The numbers below only apply to singleton pregnancies. Twin pregnancies typically have much higher hCG levels, and therefore these thresholds may not apply.
When comparing your test results, pay close attention to the post-retrieval or post-transfer date listed in the Day tested column. Some studies report by day from egg retrieval (post retrieval). Others report from day after blastocyst or embryo transfer (post transfer). HCG rises rapidly in early pregnancy, so whether a specific beta is a positive or negative signs depends on precisely when hCG was measured.
The hCG threshold for likely viability rises with each day. As one research team that examined hCG levels on different days post-retrieval reported “hCG samples … were taken on day 14, 15 or 16 after oocyte retrieval in 204 patients undergoing IVF or ICSI were analyzed… optimal cut-off levels to discriminate between viable and non-viable pregnancies… were found at 76, 142 and 223 IU/L for day 14, 15 and 16, respectively”
Interpreting your betas
If your betas are above the numbers listed in the table above, congratulations! Your pregnancy has a very high chance of continuing through the first trimester.
Note, however, that HCG is not as good of an indicator of a live birth as it is of avoiding a first trimester miscarriage–so you’re not completely off the worry hook yet. Your first ultrasound will provide better information than your beta about your chances of a live birth.
What if your hCG is below those in the above table? Don’t panic. In all of these studies about 40-60% of the pregnancies with values below the stated thresholds were ongoing. In other words, hCG was better at predicting a good outcome than it was at predicting a bad outcome. Because hCG levels vary a lot from pregnancy to pregnancy, there is no strict cutoff for determining viability.
HCG Levels during the first trimester
Normal HCG levels range widely in early pregnancy.
Below are the ranges of beta hCG by week following your Last Menstrual Period (LMP), according to the American Pregnancy Association.
- 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
- 13 – 16 weeks LMP: 13,300 – 254,000 mIU/mL
- 17 – 24 weeks LMP: 4,060 – 165,400 mIU/mL
- 25 – 40 weeks LMP: 3,640 – 117,000 mIU/mL
Serial hCG measurements
What does often indicate an impending miscarriage, however, are hCG levels that fail to double every 48 hours or that drop over time. This nearly always indicates a failing pregnancy. It can also indicate an ectopic pregnancy–an pregnancy that has implanted somewhere other than the uterus.
One final caveat: All of the above studies involved women undergoing IVF. We cannot say whether these numbers apply to women undergoing IUI or who conceived naturally.
Special case: Frozen embryo transfers
Some but not all studies find that HCG levels are lower and less predictive of miscarriage after frozen (as opposed to fresh) embryo transfers.
In Xue’s 2014 study, nearly 100% of pregnancies that made it past 12 weeks had day 12 hCG levels about 50 IU/L, as shown in the table below. But many miscarriages also had hCG levels above this threshold; 50 IU/L did not discriminate well between ongoing pregnancies and miscarriages.
A higher threshold of 135-147 IU/L performed better. Nearly 94% of pregnancies with hCG levels above this threshold were ongoing.
Have you had a beta? What was it and how did your pregnancy turn out?
(If you have had a first trimester ultrasound, you may wish to check out my post on miscarriage risk by week, by fetal heart rate, and by other risk factors like your age.)
References
Porat S, E. al. Early serum beta-human chorionic gonadotropin in pregnancies after in vitro fertilization: contribution of treatment variables and prediction of long-term pregnancy outcome. https://www.ncbi.nlm.nih.gov/pubmed/17307176
Kim, J. H. et al. Serum biomarkers for predicting pregnancy outcome in women undergoing IVF: human chorionic gonadotropin, progesterone, and inhibin A level at 11 days post-ET. Clin. Exp. Reprod. Med. 39, 28 (2012).
Kim, Y. J. et al. Predictive value of serum progesterone level on β-hCG check day in women with previous repeated miscarriages after in vitro fertilization. PLoS One 12, (2017).
Kumbak B, E. al. Serum oestradiol and beta-HCG measurements after day 3 or 5 embryo transfers in interpreting pregnancy outcome. https://www.ncbi.nlm.nih.gov/pubmed/17007661
Papageorgiou TC, E. al. Human chorionic gonadotropin levels after blastocyst transfer are highly predictive of pregnancy outcome. https://www.ncbi.nlm.nih.gov/pubmed/11704121
Xue Y, E. al. Effect of vitrification versus slow freezing of human day 3 embryos on β-hCG levels. https://www.ncbi.nlm.nih.gov/pubmed/24880883
Ochsenkühn R, E. al. Predictive value of early serum beta-hCG levels after single blastocyst transfer. https://www.ncbi.nlm.nih.gov/pubmed/19878087
Lambers MJ, E. al. Optimizing hCG cut-off values: a single determination on day 14 or 15 is sufficient for a reliable prediction of pregnancy outcome. https://www.ncbi.nlm.nih.gov/pubmed/16466846
Sung N, Kwak-Kim J, Koo HS, Yang KM. Serum hCG-β levels of postovulatory day 12 and 14 with the sequential application of hCG-β fold change significantly increased predictability of pregnancy outcome after IVF-ET cycle. Journal of Assisted Reproduction and Genetics. 2016;33(9):1185-1194. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5010803/