hCG levels in the blood 

Pregnancy tests detect a hormone called human chorionic gonadotropin or hCG. hCG begins to show up in the urine ten days from the day the woman conceives.
Pregnancy tests detect a hormone called human chorionic gonadotropin or hCG. hCG begins to show up in the urine ten days from the day the woman conceives.

"How soon can I take a pregnancy test?" 

If you've ever had that thought after having unprotected sexual intercourse, you know how important it is to understand how hCG levels rise during pregnancy

 Pregnancy tests detect a hormone called human chorionic gonadotropin or hCG. The hormone is only present in pregnant women. The hCG can be detected in the blood or urine. 

A lot of changes take place in a woman's body when she becomes pregnant. One of the quickest changes in the production of hCG. The hormone begins to show up in the urine ten days from the day the woman conceives. At-home pregnancy tests check for the presence of hCG in urine. If you use this test correctly, it can be accurate.                                                                                                                                                                                                          

Urine tests don't indicate how much hCG is present in your body. They only determine pregnancy if hCG levels are high enough to support a chemical reaction that can confirm fertilization. The test doesn't measure "how much" it measures "enough."

The hCG levels in a pregnant woman's body are highest at the end of the first trimester. The hCG levels decrease after that. In the first three weeks of pregnancy, a pregnant woman's body has 6 IU/L to 70 IU/L of hCG. The concentration increases from 160 IU/L to 32,000 IU/L during the sixth week of pregnancy. 

When should you take a pregnancy test? 

Ovulation is the process in a woman's menstrual cycle when the egg is ready for fertilization. It occurs around the 15th day of the menstrual cycle. When a sperm fertilizes a mature egg, the fertilized egg then travels to the uterus through the fallopian tubes. 

The egg implants in the uterine wall. Implantation triggers hCG production in the woman's body. The hormone is produced from the placenta's cells. A pregnancy test can detect trace hCG levels from the urine eight days following ovulation.

As more days pass, the amount of hCG increases in the blood and urine. Therefore, you're likely to get more accurate results if you take a test later with more hCG in the urine. It's recommended that you take an at-home pregnancy test on the day you expect to get your period. 

Take the pregnancy test early in the morning as the urine is more concentrated during this time of the day.

How accurate is the pregnancy test? 

An at-home pregnancy test can be very accurate if you follow the instructions on the packaging and interpret your results properly. If you do not understand or handle the test kit correctly, you'll get poor results. 

Typically, all pregnancy tests have the same ability for hCG detection. However, their ability to determine if you're pregnant or not depends on the hCG levels in your body. 

If you take a pregnancy test too close to the day of conception, the hCG levels in the body may be too low to support the chemical response. The pregnancy test won't detect the hCG, or the chemical reaction will be weak. Even if the test detects trace hCG levels, it might not clearly show that you're pregnant. 

Some women also have irregular periods, while others do not calculate the date of their period correctly. Due to this, 10 to 20 women per 100 women are unable to detect the pregnancy on the first day of a missed period

Many doctors also conduct a pregnancy test to confirm pregnancy in their patients. It is the same test as the one you would take at home. However, since doctors are usually more experienced, they are likely to get accurate results and interpret them correctly. 

Your doctor may also conduct a blood test to confirm the pregnancy. They may also have reports from other tests or findings of the physical exam to determine if you're pregnant or not. 

QUESTION

The first sign of pregnancy is most often: See Answer

How do pregnancy tests detect hCG levels?

Pregnancy tests look for a specific concentration of hCG in the body. These tests often come out negative during the early days of pregnancy since hCG levels haven't had the time to build up. 

With each passing day, the body produces more hCG to sustain the pregnancy. 

Pregnancy tests react with the hCG in urine. When you take a urine test, the hCG in the urine reacts with the paper of the pregnancy test. If there's enough concentration of hCG in the urine, you'll see double vertical lines on the pregnancy test. 

Some tests also show "pregnant" if there's enough hCG concentration. In a blood test, your blood will be drawn and sent to the lab. 

The lab will check the concentration of hCG in the blood sample. If the concentration is high enough, they will confirm the pregnancy. 

Can pregnancy tests be wrong?

All pregnancy tests detect a minimum hCG level. Some may be more sensitive than others to the concentration of hCG in your urine, but they all follow the same working mechanism. According to most manufacturers, at-home pregnancy tests have 99% effectiveness. 

However, this takes into account the condition that women are following the instructions on the pregnancy test kit properly, are taking the test at an optimal time, and are interpreting the results correctly. 

While this may sound easy, 25% of the pregnancy tests are misinterpreted as people don't understand how to read the double or single line results. Many companies now make pregnancy tests that indicate "yes" or "no." Some pregnancy tests also show "not pregnant" or "pregnant". 

An inaccurate pregnancy test can either show a false positive or a false negative. A false positive means the test shows you're pregnant, but you're not. A false negative means the test shows you're not pregnant, but you are. You may get false negatives in some situations. 

  • Test too soon: If you take a test the day after conception, your body would not have had enough time to produce detectable levels of hCG. The pregnancy test will show a false negative even if you are pregnant. 
  • Diluted urine: If you test later in the day or drink too much water before taking the test, the urine will be diluted. The test may not be able to detect hCG present in the urine due to the excessive presence of water. It's best to take a pregnancy test early in the morning when the urine is most concentrated. 

Both false positives and false negatives can be distressing, depending on your circumstances. If you suspect pregnancy, visit an obstetrician to confirm your results. 

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Medically Reviewed on 4/29/2022
References
SOURCES:

Cleveland Clinic: "Pregnancy Tests."

FDA: "Pregnancy."

Pregnancybirth&baby: "hCG levels."

UTSouthwestern Medical Center: "How early can home pregnancy tests show positive results?"