Let's talk about different topics connected to blood and urine hCG tests. We'll learn what they mean, how they're done, and how to correctly read their results. 💪

💡 This article is a part of a bigger series, based on our pregnancy test calculator.

How is a blood pregnancy test done?

When performed in a medical facility, a blood pregnancy test is pretty similar to your usual blood tests. At-home pregnancy tests are also available; they only require a single drop of blood.

At the medical office, a nurse or other medical practitioner will disinfect one of your arms, put a tourniquet on it, and then gently insert the needle into your vein to take a blood sample. That's it, you're done! And if you were wondering, yes, you may eat freely before the appointment — it won't affect your pregnancy test results. 🍔

After 24–48h, you'll receive results that may either confirm or rule out the pregnancy: the amount of hCG (human chorionic gonadotropin) in your bloodstream. The hCG is a hormone produced throughout your pregnancy, even at its early stages. Levels of hCG in the blood are usually higher than those in urine — that's why you're able to find out about your pregnancy earlier.

Visit the hCG levels calculator if you'd like to know something more on the subject.

Will I need to do anything to prepare for the test?

The blood pregnancy test requires only your willingness and an appointment at the medical office. You may eat and drink before the test.

If you haven't performed any home urine or blood tests yet, it's good to calculate how many days have passed since your last period and if you've already missed your next one. It's best to take a pregnancy test one or more days after the expected date of your next period — if you do it too early, the amount of beta-hCG in your blood might be too low to detect.

Suppose you've missed your last period, and you're experiencing evident symptoms of pregnancy. In that case, it is best to do the diagnostic test and see your doctor as soon as possible. You'll both confirm the gestations and estimate the week of pregnancy. 🤰

Are there any risks to the test?

The risks associated with the hCG blood test are no different than those of a regular blood draw. These risks include discomfort, bruises, and infections limited to the small area of skin where the needle enters your veins.

If you wish to make it even easier, you might perform one of the available home pregnancy tests that can use both blood and urine. They all look for hCG in your blood, and their test kits look pretty similar — however, they usually differ in accuracy, especially in detecting early pregnancies.

What do the results means?

There are two main types of pregnancy tests: qualitative hCG and quantitative hCG. We know that these two names sound pretty similar, but they do convey a different information. 🙋

  • The qualitative hCG test checks for the presence of the gestation. It informs us whether the hCG level has exceeded 25 U/L, a threshold above which we can clearly confirm a pregnancy. Its results are extremely straightforward; either you're pregnant or you're not.

  • The quantitive blood test can detect hCG and tell us its exact level. The test results are usually given as a number. These outcomes do not only serve as a pregnancy confirmation; this type of test can be used to rule out an ectopic pregnancy or detect some problems associated with the first trimester.

Blood tests can be also used in prenatal diagnostics. They serve as the first trimester screening that may diagnose many possible problems during pregnancy. These results shouldn't be interpreted on their own — contact your doctor to find out more about your outcomes.

Read more about the implantation process and the menstrual cycle in the implantation calculator.

Can blood tests detect pregnancy at 3 weeks?

In order to answer this question, we need to first think about a single question: what does it really mean to be 3 weeks pregnant?

This might sound surprising, but all women are already 2 weeks pregnant at the moment of conception! But, why is that so? 🤷‍♀️

Doctors count the time of the pregnancy from the first day of your last period, which is the beginning of the menstrual cycle when the conception took place. Usually, the time between this date and the creation of a new life takes around 14 days!

Now we can come back to the primary problem of ours — the pregnancy blood tests. On average, such a test may turn out positive even after 8–10 days after conception, or between the 3rd and the 4th weeks of the pregnancy! However, it is always better to wait at least a few more days — low levels of hCG produced early in pregnancy may often result in false-negative outcomes.

Can a pregnancy blood test be wrong?

Yes, such a situation is possible, but it's very unlikely. The blood tests results are incredibly accurate and way more precise than the typical home urine tests available in pharmacies.

However, it is possible to receive false-negative or false-positive results in some extremely rare cases. This situation might be caused by faulty labeling, mixed samples, or just simple equipment malfunction. For example, the false-negative result may occur if the beta-hCG test was performed too early.

If you suspect your home kit to be faulty, take another test and visit your OB-GYN. Your doctor will perform the ultrasound scan and gynecological examination to finally confirm your pregnancy.

Is the blood test most accurate for pregnancy?

Yes, the results obtained via blood tests are way more accurate than the ones obtained with home pregnancy kits.

The traditional blood tests are performed in a laboratory, using better equipment, and they also eliminate the possibility of user error. We also need to mention that the hCG is first released into your blood, and only then is passed into urine. All these reasons combined serve as an explanation on why it is possible to obtain the negative urine pregnancy test, and simultaneously test positive with the blood test.

What if the pregnancy blood test is positive, but urine test is negative?

This situation may happen when the hCG levels are too low to be revealed by the standard home pregnancy kit, but are high enough to be caught by the more precise lab methods.

Such a situation may also occur if the urine test has expired or was defective from the very beginning. The C-line (control line) must always appear in the test window. If it's not there, it means that your test is faulty, and you must repeat it.

Will a blood test show pregnancy after miscarriage?

The blood test should turn negative after miscarriage. HCG (human chorionic gonadotropin) levels drop significantly in the two days following a miscarriage. The small residuals of this hormone can be seen even a few days or weeks afterwards, and should be monitored to rule out the possibility of severe diseases like choriocarcinoma or molar pregnancy.

If your hCG stays on the same level or keeps increasing, you need to see your doctor as soon as possible. 📍

Łucja Zaborowska, MD, PhD candidate
Have you been wondering when to take a pregnancy test?

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