How Early Can Pregnancy Be Detected with a Test?

  • Positive Pregnancy Test: when will a pregnancy test show positive?

Among the most important questions asked by women is "How soon can I detect my pregnancy"? A pregnancy can be detected mainly by a missed period and implantation bleeding as well as through different ways such as typical pregnancy symptoms, and early positive pregnancy tests. Another way to detect your pregnancy is by doing our "Am I pregnant?" pregnancy quiz test, and the online pregnancy test (OPT).

Pregnancy Test - Overview

A pregnancy test is a test to detect the pregnancy hormone hCG (human chorionic gonadotropin) in the blood or urine to determine whether or not a woman is pregnant.

hCG measurement

How early can pregnancy be detected depends on finding the hCG hormone, and all tests currently available to test for the presence of a pregnancy look for the presence of the beta subunit of hCG or human chorionic gonadotropin in the blood or urine.

HCG can be detected in urine or blood after implantation, which occurs on average 9 daye (range 6-12 days) after fertilization. Some home pregnancy tests claim to detect hCG as early as 4 days before the next expected period. Whether that statement is accurate for an individual woman depends on the length of her luteal phase and on how soon that individual embryo implanted. Quantitative blood (serum beta) 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. Qualitative blood tests generally have a threshold of 25 mIU/mL, and so are less sensitive than some available home pregnancy tests.

Pregnancy Test detection

This hormone is released by trophoblastic tissue in the placenta and it's presence decides how early can pregnancy be detected. In rare cases, it may be produced by a choriocarcinoma or some other germ cell tumours, or even other forms of cancer, e.g. lung cancer.

Doubling rule

Doctors can also perform quantitative serum beta hCG levels. The measurement is done in mIU/ml, and a level above 25 mIU/ml usually indicates the presence of a pregnancy. 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 for 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.

Quantitative beta hCG readings are also used in evaluation of trophoblastic and other germ cell tumors.

gstational sac pregnancy

Correlation to obstetric ultrasonography

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

False positive pregnancy tests/ False negative pregnancy tests

A false negative pregnancy test is a pregnancy test that is negative but you are in fact pregnant. This usually happens when testing is done too early. You are pregnant but you test negative. Quantitative blood tests and the most sensitive urine tests usually detect hCG shortly after implantation, which can occur anywhere from 6 to 12 days after ovulation and implantation is usually the deciding factor to answer the question how early can pregnancy be detected. Beta hCG levels rise exponentially in the first two months or so 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. Menstruation occurs on average 14 days after ovulation, so the likelihood of a false negative is low once a menstrual period is late.

A false positive pregnancy test is a pregnancy test that is positive but you are not pregnant. This can result from conditions like

  • choriocarcinomas
  • IgA deficiencies
  • heterophile antibodies
  • enterocystoplasties
  • gestational trophoblastic diseases (GTD)
  • gestational trophoblastic neoplasms (GTN)
  • testicular germ cell malignancies
  • hCG injection

Many home pregnancy tests may show a positive or unclear result when read 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. Additionally anyone who has been given an hCG injection would also give 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 thus they will display a consistently low positive blood pregnancy test even though they are not pregnant. This phantom hCG may lead to serious misdiagnosis and intervention, but can be detected with serial dilutions and tests. Patients with phantom hCG have a positive blood hCG but a negative urine hCG test.