Whether you're trying to conceive (TTC) or you're done having babies (or anywhere else in between), knowing for certain if you are pregnant is a big deal. People who are actively trying to get pregnant are especially eager to know if they are pregnant as early as possible into the process. (Intra-uterine cameras anyone??)
The question then becomes, just how early can you know? The short answer is: it varies. Depending on the method by which you use to determine your pregnancy, the length between conception and/or fertilization and knowing you're pregnant can be markedly different. Let's take a look at the possibilities.
Fertilization of an egg (when the sperm successfully enters the egg and the development process begins) can occur anytime from a few hours up to five days after sex or insemination, depending on if ovulation (released an egg) has already happened and the egg is ready and waiting, or if ovulation happens after sperm are released.
Some people just know they're pregnant. These are the same kinds of people who just know it's going to rain (regardless of forecasts) or just know something is wrong. They have a strong sense of self and intuition, and most of the times, their "gut feelings" are correct.
Physiological changes/physical symptoms: 3-4 weeks
Based on how you feel physically, there are a lot of different markers that can signal pregnancy. Unfortunately, many of these symptoms can also signal your period and normal monthly hormonal changes.
At around 4 weeks, if you are pregnant, you will not have a period. A missed or late period is often the first sign for many people, especially if you have a predictable cycle.
Other physical symptoms that could indicate a pregnancy include cramping, back ache, nausea, headaches, fatigue, heightened or sensitive smell, mood swings, and bloating. During this time, you may also experience "implantation bleeding," which is a light spotting of blood that can occur when the fertilized egg implants itself into the lining of your uterus. It can happen around 6 to 8 days after conception, but not everyone experiences the spotting.
Tracking/charting: 3-4 weeks
If you are tracking and charting your fertility and symptoms using natural family planning methods and basal body temperature (BBT) readings, you may get good signs that you might be pregnant even before you miss your period. Ultimately, though, BBT readings are most likely to be more accurate for a positive pregnancy around the time you would expect your period.
Charting fertility involves daily recording of changes in BBT and cervical mucous, alongside tracking intercourse or insemination. When there is a rise in BBT, it can indicate that ovulation has occurred. If you had sex around the time of ovulation, pregnancy is more likely to take place. People who track BBT also look for a temperature dip around the time of implantation, as well as a second rise in temperature that happens around one week after ovulation. Both of these can happen normally, or can be signs of pregnancy.
Pregnancy test (pee on a stick): 3 weeks
Pee-on-a-stick (POAS) pregnancy tests detect pregnancy by the amount of hCG (human chorionic gonadotropin) hormone levels in your urine. This hormone is present (and begins growing) at the time of implantation, which is 6-12 days after ovulation. Different POAS pregnancy tests have different levels of sensitivity. Some tests can detect as little as 10 mIU hCG in your urine. hCG doubles every 48-72 hours, so the longer you wait to test, the more hCG present, the more accurate the pregnancy test results. The earlier you take a pregnancy test, the less reliable the results. While you may get a positive POAS test at 3 weeks, it's a good idea to wait a week or two and test again to confirm.
Blood test: 3 weeks
A blood test also can detect hCG and is more sensitive than a urine test. Since it can detect pregnancy as early as 6 days after ovulation, you could be able to confirm your pregnancy at/around 3 weeks. The downfall is that most doctors will not order a blood test this early to determine pregnancy unless there is a medical reason to do so.
Ultrasound: 4-6 weeks
Traditional ultrasound (wand placed on lower abdomen) and transverse ultrasound (wand placed inside the vagina) can detect a gestational sac about one week earlier than it can show a fetus (baby). Transverse ultrasound is used when the gestational sac or baby cannot yet be seen using the traditional ultrasound. Most doctors wait until 6-8 weeks to use ultrasound to detect pregnancy, unless there is a medical reason to do so earlier.
Doppler (detect heartbeat): 8-12 weeks
Detecting pregnancy by listening for the heartbeat with a doppler machine (wand placed on abdomen) cannot be used reliably until at the very earliest 8 weeks, but often closer to 12 weeks.