How early can a blood test determine pregnancy

Since the earliest recorded history, women have had a strong desire to know whether they are pregnant as early as possible. The body goes through countless changes in the first trimester, and one of the first indicators is a change in the hormones that leave the body through urine.

Ancient Egyptians relied on a form of urine testing to determine pregnancy status way back in 1350 BCE. A woman urinated daily on wheat or barley seeds and if the plants grew, it meant she was pregnant. Modern-day validation suggests that test was about 70% accurate in detecting human chorionic gonadotropin (hCG), a hormone produced by a woman’s body soon after implantation of a fertilized egg inside the uterus.

Thankfully, urine-based pregnancy tests have evolved substantially. Women now have access to advanced tests that can detect a pregnancy as early as eight days after ovulation. But while many home pregnancy tests are marketed as simple and effective, getting accurate results comes down to how early in your ovulation cycle you take the test.

Ovulation generally occurs around day 15 of a 28-day cycle. In a normal pregnancy, an egg is fertilized in the fallopian tube and then travels into the uterus, where it implants in the uterine wall. After implantation, production of hCG starts from cells in the developing placenta (tissue that will feed the fetus). Trace levels of hCG can be detected as early as eight days after ovulation.

That means you could get positive results several days before you expect your period to start. However, the first part of your cycle is more variable than the second, making it tricky to determine the best time for an early test.

Pregnancy test accuracy

Each type of pregnancy test is designed to detect a set minimum level of hCG. This is why pregnancy test manufacturers advertise the way they do: “Know four days sooner,” or “Accurate up to six days before a missed period.” However, while home pregnancy tests are quite accurate – many boast a 99% detection rate based on laboratory testing results – marketing claims can be misleading.

For example, a 99% detection rate means a test can detect hCG 99% of the time on the day you miss your period. These statistics also assume that women are testing at the optimal time and following all instructions correctly.

Many home pregnancy tests available today are midstream urine dip tests, which are the traditional “pee-on-a-stick” tests and are fairly easy to use. There also are tests in which you pee into a cup and dip a test strip into the urine. The New York Times published a story ranking the best home pregnancy tests, citing a midstream test with an ergonomic grip as the easiest to use and most accurate.

Research has shown that average test results when women used the dip tests matched lab test results just 70% of the time, whereas 99% of women typically can get an accurate reading from a midstream test.

When to see a doctor

Most women who have a positive pregnancy test should wait a week or two before calling the Ob/Gyn office for a pregnancy blood test or ultrasound to confirm the pregnancy. We suggest waiting because the rate of early pregnancy loss is high, and it’s possible that you might have had a chemical pregnancy.

However, women with a history of ectopic pregnancy or current abdominal pain should call the doctor right away to be examined. Ectopic pregnancies implant outside of the uterus and produce hCG, resulting in positive pregnancy tests. However, these pregnancies can cause abdominal bleeding and prompt medical care is necessary. Women who have congenital heart defects or other chronic physical or mental health conditions should also see a doctor right away because treatment plans or medications might need to be altered to protect the woman and the fetus.

Advances in home pregnancy tests give women greater insight into what’s going on in their bodies sooner than ever before. No matter what your childbearing plans might be, it’s essential to get quick, accurate results at home to plan your next steps accordingly.

Most pregnant women find out they are pregnant by taking a urine-based home pregnancy test. Sometimes, doctors suggest that you also take a blood pregnancy test. In specific cases, there are multiple reasons why a blood test may be preferred, but usually, a urine test is all you need. Below, we explain exactly what a blood pregnancy test is and how it differs from a urine test.

Overview

A blood pregnancy test is usually a quantitative blood test that shows how much human chorionic gonadotropin (hCG) is in your blood. This is the type of blood pregnancy test that most people are referring to when they talk about blood tests for pregnancy. To test your blood for hCG, a simple blood sample is taken from one of your veins, usually in the arm, through a procedure called a venipuncture.

HCG is a hormone secreted in pregnancy and detectable beginning a week to two weeks (or more) after conception, depending on the test. Whether using a home pregnancy test that uses urine or a blood pregnancy test from your doctor, the results will be based on measurements of this hormone in your urine or blood. Both types of tests are very reliable, producing about 99% accuracy when used correctly.

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What's the Difference?

A pregnancy blood test is more sensitive than a urine test and can offer more information. Most blood tests can detect slightly lower amounts of hCG, which means they can tell if you're pregnant a few days earlier. Urine tests tend to require slightly more hCG to read positive, making false-negative results a bit more likely with urine tests, although the rates are quite low overall.

Urine hCG Test

• Needs slightly more hCG for a positive reading

• Qualitative test

• Tells you if you are pregnant or not, not how much hCG is in your blood

• Accurate a few days to a week after a missed period

Blood hCG Test

• Slightly more sensitive than urine tests

• Can be qualitative or quantitative

• Can track hCG levels over time

• Can be accurate before a missed period

Qualitative Tests

Urine tests are qualitative, meaning they either detect hCG in your blood, giving a positive reading, or they don't, which is a negative reading. You may also have a qualitative blood hCG test to measure hCG in your blood. Again, the results are very clear: yes, you are pregnant because we found hCG in your blood or, no, you are not pregnant because we didn't find it.

Urine pregnancy tests can usually detect pregnancy by about 10 days after conception. Blood pregnancy tests can pick up hCG in the blood six to eight days past ovulation.

It's recommended to wait a week (or at least a few days) after a missed period before taking a urine pregnancy test for optimal efficacy.

Quantitative Tests

Another option is getting a quantitative hCG blood test (also called the beta hCG test). These tests can give your doctor or midwife more information than just whether or not you're pregnant. Quantitative hCG tests can pick up even tiny amounts of the hormone and measure exactly how much hCG is in your blood. This information can be compared over time.

In general, your hCG levels will nearly double about every two days in early pregnancy.

By having multiple blood tests about 48 hours apart, your doctor can track your hCG levels to get a better read on your pregnancy, if needed. These serial blood tests can help your provider monitor your pregnancy for miscarriage or ectopic pregnancy as well as the possibility that you’re carrying multiples.

Due to stress, expense, and other factors, these tests are not done routinely (or needed) for every pregnant woman. Talk to your doctor or midwife if you think that a blood test for pregnancy is right for you. If your specific circumstances don't warrant a blood test, you should be able to rely on the results of your home pregnancy tests (HPT) instead.

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When a Blood Test Is Used

In routine pregnancies with healthy women, at-home urine tests are more than sufficient and effective. Blood tests are primarily used in doctors' offices, specifically, if there is a potential issue with the pregnancy or some other complicating factor (such as multiples), in which the greater sensitivity of the blood test is needed.

Blood tests may be ordered for higher risk pregnancies, during fertility treatments, when urine tests read negative but a period hasn't come, to confirm or rule out a possible miscarriage or multiples, and to diagnose a potential ectopic or tubal pregnancy, as well as due to other pregnancy complications.

Efficacy of Urine vs. Blood Pregnancy Tests

Urine tests are low-cost, painless, easy-to-use, can be done in the privacy of one's home, and are very accurate (in most scenarios), which is why they are the standard test used for most pregnancies.

A blood pregnancy test is warranted due to complicating factors. These tests are also very accurate, providing quick results that can give doctors more detailed information about your pregnancy.

Interpreting the Results

Normal results from a quantitative hCG blood pregnancy test would show that hCG levels are rising rapidly during the first trimester of pregnancy and then declining slightly after around 10 weeks. At around 16 weeks, the hCG levels stabilize for the remainder of the pregnancy. Abnormal results, on the other hand, can mean a variety of things.

Higher hCG Than Expected

A higher than normal level of hCG may indicate:

• Infection or malignant tumors of the uterus
• More than one fetus (for example, twins or triplets)
• Non-cancerous tumors of the uterus
• Ovarian cancer
• Sometimes, just an indication of a normal pregnancy, farther along in gestation
• Testicular cancer (in men)

Lower hCG Than Expected

Lower than normal levels of hCG may mean:

• Ectopic pregnancy
• Incomplete or complete miscarriage
• Possible death of the fetus

Understanding the Risks and Causes of Miscarriage

Risks

There is very little risk associated with a blood pregnancy test. Aside from minor pain when the needle is injected, most people don't have any other side effects from having blood drawn. Occasionally, some people will have bruising at the site of the injection.

In rare cases, some people experience excessive bleeding, fainting, or infection from having blood drawn. Let your doctor know if you have ever had an issue with having blood drawn. 

A Word From Verywell

For most women, a urine-based, at-home pregnancy test will more than suffice to confirm pregnancy. Occasionally, a blood pregnancy test, either the qualitative or quantitative type, is needed to provide more information, particularly in medically complex situations. Both tests are safe, simple, and effective ways to know if you are pregnant. Blood tests are best when something else might be going on.

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