Pregnancy is a period of approximately 9 months and 10 days during which one or more babies develop inside a woman's uterus. While pregnancy usually occurs through sexual intercourse, it can also be achieved through assisted reproductive technologies.
Pregnancy can result in live birth, spontaneous miscarriage, elective abortion (induced abortion),or stillbirth. Birth typically occurs about 40 weeks from the start of the woman’s last menstrual period, or approximately 38 weeks after fertilization.
Pregnancy begins when a fertilized egg (embryo) attaches to the uterine wall about 5–6 days after fertilization. The term "embryo" is used from the first day of the last menstrual period up to the tenth week of pregnancy. After that, the developing baby is referred to as a "fetus" until birth.
One of the most exciting and joyful moments for expecting couples is seeing a positive result on a pregnancy test. Whether the pregnancy is planned or occurs after unprotected intercourse, symptoms can vary widely from one woman to another. These symptoms may include:
When one or more of these symptoms are experienced, a pregnancy test is necessary to confirm the diagnosis, as these signs could also indicate other medical conditions.
Throughout history, pregnancy testing methods have evolved based on technological capabilities. Today, with advances in medical science, pregnancy can be accurately confirmed using urine and blood tests.
Often referred to as the "pregnancy hormone," hCG (Human Chorionic Gonadotropin) is produced exclusively by the placenta during pregnancy.
Fertilization occurs in the fallopian tubes when a woman’s egg is fertilized by a man’s sperm, forming an embryo. The outer layer of the embryo develops trophoblastic cells, which help it implant into the uterine wall. These trophoblastic cells secrete the hormone known as hCG. The sole purpose of hCG is to support pregnancy.
The hCG hormone plays a vital role in early pregnancy by maintaining the corpus luteum in the ovary and supporting the uterine lining to allow embryo implantation. Because hCG is produced by the fertilized egg and later the placenta, it is the key hormone used to detect pregnancy.
About 5–6 days after fertilization, the embryo implants into the inner lining of the uterus and begins producing increasing amounts of the hCG hormone. hCG can be detected in blood or urine approximately 10 to 11 days after conception (when a sperm fertilizes an egg). However, it takes a bit longer for hCG to be detected in urine tests.
Since the expected period hasn’t yet occurred, many women are unaware of this process. Although hCG may already be present in blood and urine, tests performed before the expected menstrual date may not reliably confirm pregnancy.
If there is a delay in the expected period, hCG levels in blood or urine can be measured to determine whether pregnancy has occurred. Tests done before the expected date do not provide definitive results. Note that hCG tests are different from ovulation tests—ovulation tests only indicate ovulation timing and cannot confirm pregnancy.
Taking a test too early or miscalculating the last menstrual period may result in low or negative test results. In such uncertain cases, the test should be repeated a few days later.
Pregnancy tests detect the presence of human chorionic gonadotropin (hCG),the pregnancy hormone, in your urine.
After conception, your body begins producing hCG. If you get a positive test result on the first day of your missed period, it likely means you conceived about two weeks earlier.
More sensitive tests can detect pregnancy as early as 8 days after conception. Some pregnancy tests may even estimate the time of conception based on the level of hCG in your urine.
Women who suspect pregnancy can confirm it by taking an hCG test via blood or urine. These tests can be easily done at home or in medical facilities. hCG can be detected earlier in blood than in urine.
A blood test taken from the arm provides more precise information about hCG levels and can even help estimate how far along the pregnancy is. A urine test simply indicates whether or not pregnancy has occurred. The best sample for a urine test is the first urine of the morning.
Home pregnancy tests are typically performed using urine on the first day of a missed period. These tests detect the pregnancy hormone known as hCG in the urine. If pregnancy is present, a chemical substance on the test stick reacts with the hCG hormone, causing a color change. After applying urine to the designated area, it's important to check the result after about 5 minutes. Although waiting times may vary depending on the test brand, they typically range from 3 to 5 minutes.
Modern home pregnancy tests are generally very reliable. However, if a positive result is obtained, it is essential for the woman to consult a healthcare professional to confirm the pregnancy and begin prenatal care if necessary.
Clinical pregnancy tests are conducted through blood analysis. These tests detect hCG in the blood and are divided into two types: quantitative and qualitative.
Results may vary depending on the laboratory, testing method, or equipment used to measure hCG. The hormone is measured in milli-international units per milliliter (mIU/mL).
Blood hCG levels are interpreted as follows:
If the hCG level is below 50 IU/L, the test may need to be repeated after 48 hours to monitor whether hCG levels are rising.
Home urine tests determine whether pregnancy is present. The hCG hormone begins to be secreted in measurable amounts around 7 to 10 days after fertilization. However, if the test is taken too early, it may show a false negative. Therefore, it is advisable to wait until the expected date of the period before testing.
Different pregnancy tests on the market have varying sensitivity levels. Some tests can detect lower levels of the hormone, while others require higher levels of hCG for a positive result. If the test is negative but menstruation still hasn’t occurred, the pregnancy test should be repeated.
It is natural to seek confidence in the reliability of pregnancy test results. Most home pregnancy tests are about 99% accurate when used correctly. However, a false positive result, although rare, can occur due to several reasons.
Residual hCG levels can remain in the body for a short time after a miscarriage or abortion, leading to a false positive test.
The earliest a pregnancy test can be taken is the day after a missed period. The earlier the test is taken, the higher the chance of getting a false negative—even if you are pregnant. If you have irregular menstrual cycles and your expected period date is uncertain, it’s generally recommended to wait until your longest cycle length has passed.
For example, if your cycle ranges between 30 to 36 days, the ideal time to test would be on day 37 or later. Some early-detection pregnancy tests may be able to detect pregnancy a few days before your expected period, but the most accurate results come from testing after a missed period.
When used as instructed, most urine pregnancy tests claim 99% accuracy after a missed period. However, this accuracy does not apply to tests taken before the expected period.
If your period is expected on a Wednesday and does not arrive, the earliest recommended time to test would be Thursday.
The first morning urine is typically more concentrated and can detect hCG more accurately. Therefore, testing with the first urine of the day increases the accuracy of the result. However, a pregnancy test's accuracy can depend on several factors:
When performing a urine pregnancy test, the test stick is either held in the urine stream or dipped into a container with collected urine. After a few minutes, the stick displays the result—usually as a plus or minus sign, one or two lines, or words like "pregnant" or "not pregnant."
You should always follow the instructions to know how long to wait before reading the result—typically at least two minutes. Most tests also include a control indicator—a line or symbol that appears in the result window. If this line or symbol does not appear, the test is not functioning properly and should be repeated with a new test.
Some home pregnancy tests are more sensitive than others. In other words, they can detect lower levels of hCG in urine. Before using a test, it's important to check the expiration date and carefully read all instructions.
Blood tests can detect lower levels of hCG and confirm or rule out pregnancy earlier than urine tests. Blood pregnancy tests are approximately 99% accurate.
In the very early stages, even after a positive pregnancy test, the gestational sac may still be too small to be seen on ultrasound. Typically, about two weeks after a positive test, an ultrasound can detect the gestational sac and fetal heartbeat.
Low hCG levels are generally associated with adverse pregnancy outcomes. While low hCG levels may indicate potential problems, there are conflicting data regarding their relationship with poor pregnancy outcomes in the absence of fetal chromosomal or structural abnormalities.
Some studies have found a significant association between low hCG levels and complications such as fetal loss, intrauterine growth restriction, and low birth weight. However, other studies have not demonstrated these associations.
The relationship between high hCG levels and adverse pregnancy outcomes is controversial. Some studies have shown that elevated hCG levels during the second trimester are associated with a range of pregnancy complications, including late fetal loss, gestational hypertension, preeclampsia, intrauterine growth restriction, preterm birth, and stillbirth. However, other studies have not confirmed these associations.
In IVF treatments, a pregnancy test can be performed 14 days after egg retrieval, 12 days after a day-3 embryo transfer, or 10 days after a day-5 embryo transfer. A blood or urine test will detect and measure the "pregnancy hormone" hCG. During early pregnancy, hCG levels typically double every 2 to 3 days.
Home pregnancy tests can be purchased over-the-counter at pharmacies. The price of pregnancy tests varies depending on the brand, but most tests are not expensive. Blood pregnancy tests tend to be more costly than urine tests, and their price varies depending on where the test is performed.
Prof. Dr. Nilgün TurhanGynecology, Obstetrics and IVF Treatment Specialist
PROF. DR. NILGÜN TURHAN
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