Deciphering the math of βhCG levels

Deciphering the math of βhCG levels

by Crystal Chan, author on The Conception Diaries Crystal Chan 15 March 2017

The one-to-two-week wait to do your first βhCG test to confirm pregnancy can be one of the toughest parts of fertility treatment. Whether you’ve had intercourse, done an intrauterine insemination or had an embryo transferred after IVF, doing the blood test earlier than directed by the fertility clinic is not advised because it’s unlikely to be helpful. So, brace yourself for the wait, and read this so you know what to expect if it turns positive!

What is βhCG?

βhCG is a hormone produced by the embryo and is only detectable in your blood or urine if the implantation has occurred. Testing βhCG in urine simply confirms pregnancy, but blood testing is able to measure specific levels of the hormone. The level of this hormone normally rises as pregnancy progresses, until it peaks at about 10 weeks of pregnancy.

What does the βhCG level tell us?

Before the pregnancy becomes visible on ultrasound, the βhCG levels can give us clues about how and where the pregnancy is developing. There is no specific βhCG level that can tell us whether the pregnancy will ultimately be successful. However, the trend of the βhCG levels on repeated measurements can help us predict outcome.

Typically, we like to see the βhCG level rise by at least two thirds every two days. This reassures us that the embryo is developing appropriately. If the βhCG levels are rising more slowly than this or even decreasing, then the likelihood of miscarriage or ectopic pregnancy is higher.

An ectopic pregnancy is a potentially life-threatening condition that occurs in 1 to 2% of pregnancies, where the embryo grows outside of the uterus, often in the fallopian tube. If the βhCG trend is abnormal, we advise patients to watch for pain and abnormal bleeding, which could be symptoms of ectopic pregnancy. An abnormal trend prompts us to watch the pregnancy more closely and may lead to treatment if the pregnancy does not develop normally.

One thing to emphasize is that the βhCG is not a perfect test. There are pregnancies that have a normal βhCG rise that end up unsuccessful. There are also pregnancies with a slightly slower rise in βhCG that result in healthy babies. So, think of the βhCG level as a rough guide until about six to seven weeks of pregnancy.

Once the βhCG rises to 1500 to 2000 units, that’s when a vaginal ultrasound should be able to visualize a pregnancy in the uterus. And at that point, ultrasound takes over as the best test to monitor the development of your baby.

So, sit tight — there’s not much you can do — and think positive thoughts. You got pregnant! And no matter what, that’s a step in the right direction.

Crystal Chan, guest author on The Conception Diaries Guest author: Crystal Chan is a Fellow of the Royal College of Surgeons and Physicians of Canada, with dual specialization in obstetrics and gynecology and reproductive endocrinology.