What is the best way to find out if you are pregnant?

Among the most popular questions asked by couples trying to get pregnant is "How soon can I detect a pregnancy"? Pregnancy can be gauged by a missed period, typical pregnancy symptoms,  implantation bleeding, and confirmed by a positive pregnancy test. (Another way to detect your pregnancy is by taking our online pregnancy test.)

When can you take a home pregnancy test? 

A pregnancy test detects the pregnancy hormone hCG (human chorionic gonadotropin) in the blood or urine to determine if a woman is pregnant. How early pregnancy can be detected depends on finding the hCG hormone. hCG can be detected in urine or blood after implantation, which occurs on average, about 9 days (range 6-12 days) after fertilization. Some home pregnancy tests claim to detect hCG as early as 4 days before the next expected period yet that claim depends on your luteal phase and how soon the embryo implanted. Quantitative blood tests can detect hCG levels as low as 1 mIU/mL, while urine tests have published detection thresholds between 20 and 100 mIU/mL, depending on the brand.

How does hCG doubling affect pregnancy?

Doctors can also perform quantitative serum beta hCG levels via a blood test.  Two tests are usually necessary to verify a normal increase, usually 2-3 days apart. The increase in serum hCG can be interactively monitored.

• Below an hCG level of 1,200 mIU/ml, the hCG usually doubles every 48-72 hours, though a rise of 50-60% is still considered normal and determines how early can pregnancy be detected.
• Between 1,200 and 6,000 mIU/ml serum, the hCG usually takes 72-96 hours to double.
• Above 6,000 mIU/ml, the hCG often takes more than four days to double.

Failure to increase normally may indicate that the pregnancy is not developing well, and can be an early sign of a possible miscarriage or an ectopic pregnancy. After a miscarriage, hCG levels fall steadily back to the non-pregnancy range. Also, an ectopic pregnancy may be suspected when hCG levels fail to double, particularly if the hCG level rises, falls and rises again.

When can an ultrasound confirm pregnancy?

On ultrasound, how early pregnancy can be detected depends on seeing the gestational sac, or the embryo. Once a pregnancy has advanced past the first 6-8 weeks, it is usually easier to follow by sonography as more information is obtained in real time. In general, pregnancy is detectable 25 days after ovulation by transvaginal sonography (which usually corresponds to an hCG level of 1,500 ml).

What about false positive and false negative tests?

A false negative pregnancy test usually happens when testing is done too early, and you are pregnant but you test negative. hCG levels rise exponentially in the first two months of pregnancy so the earlier the test is performed, the higher the chance of a false negative result. Less sensitive urine tests and qualitative blood tests may not detect pregnancy until three or four days after implantation.

A false positive pregnancy test is a pregnancy test that is positive but you are not pregnant. Home pregnancy tests may show a positive or unclear result when reading well after the suggested 3-5 minute window, independent of an actual pregnancy. This type of false positive is also known as an evaporation line.

Also, anyone who has been given an hCG injection will also get a false positive. In addition, a false positive can also be seen in patients with a "phantom hCG". These women have a low positive blood pregnancy test and a negative urine pregnancy test. Phantom hCGs are seen in some individuals who react to some substrate in the blood pregnancy test and display a consistently low positive blood pregnancy test even though they are not pregnant. This phantom hCG may lead to misdiagnosis but can be detected with serial dilutions and tests. Patients with phantom hCG have a positive blood hCG, but a negative urine hCG test.