How Long After Sex Can Pregnancy Be Detected?

white pregnancy test showing 1 red line

Typically, it’s best to wait until you miss your period to take a pregnancy test. However, understanding how long it takes for sperm and an egg to meet, fertilize, and implant can help you know when you can start testing.

Pregnancy tests work by detecting the hormone human chorionic gonadotropin, or hCG. But your body won’t produce hCG until the fertilized egg attaches to your uterus.


To conceive, sperm must meet up with an egg. This usually happens in the fallopian tubes. Once that happens, the fertilized egg travels down the tube to the uterus, where it attaches to the lining of the uterus. The fertilized egg now has a new job: to keep dividing and growing.

A fertilized egg that successfully attaches to the uterus is considered pregnant. Pregnancy tests work by measuring a hormone called human chorionic gonadotropin (HCG). Most urine tests can detect HCG between 10 and 14 days after conception, says Copperman. Blood tests can detect it earlier, around 10 to 12 days after conception.

Your fertile window is the period of time during your monthly cycle when you can conceive. A woman is most fertile 3 days before ovulation and 24 hours after ovulation. If a woman has unprotected sex during that window, fertilization may occur.

This is why it’s usually recommended to wait until you miss your next period before taking a pregnancy test, particularly if you use birth control. However, some people can get a negative result before their period is due. This can be frustrating, especially if you’re worried about getting a false positive. A better approach is to take a test before your next expected period starts, especially if you track your menstrual cycle or know your ovulation date.

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For a woman to get pregnant, the egg in one of her ovaries must be fertilized. This is what happens during sexual intercourse. About every month, about halfway through the menstrual cycle, a mature egg is released from one of the ovaries. This is called ovulation. The egg only has about 24 hours to be fertilized before it dies and is flushed away in the menstrual flow. Sperm, on the other hand, can survive for up to five days. Fertilization occurs when sperm and an egg meet in the fallopian tube. A fertilized egg then makes its way down the fallopian tube to the uterus, where it attaches to the lining of the uterus and becomes a fetus.

Most home pregnancy tests work by detecting a certain hormone, human chorionic gonadotropin, or hCG, in the urine. Generally, the body does not produce enough hCG to trigger a positive test result until it is at least two weeks past ovulation.

For women who have a regular 28-day menstrual cycle, the day of ovulation usually falls on or around day 14 of the cycle. Therefore, for most women, the best time to take a pregnancy test is after they miss their period. However, if a woman is worried about getting pregnant after unprotected sex and wants to know if she is pregnant before the missed period, she can use an ovulation predictor kit to check for ovulation.

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It can be tempting to take a pregnancy test right after unprotected sex, but it’s best to wait until you miss your period. It takes time for the body to make enough of the hormone human chorionic gonadotropin, which pregnancy tests detect, and you won’t get an accurate result until then.

During sexual intercourse, sperm swim up to the egg and fertilize it. Conception can happen within minutes after sex, but it’s not considered pregnancy until the fertilized egg—now an embryo—implants itself into the lining of the uterus. This process can take up to five days after sex.

Many women experience spotting or bleeding around the time of implantation, and it may be confused with a period. It’s normal, but it’s important to talk to your doctor if you experience it.

Home pregnancy tests are highly accurate, but you’ll get the most accurate results by waiting until you miss your period. If you can’t wait, consider getting a blood test to confirm your results or buying a digital early pregnancy test from a doctor or Planned Parenthood clinic that offers sliding-scale testing. These are more expensive than most over-the-counter pregnancy tests, but they’re more reliable. You can also ask your health care provider about the most reliable methods of contraception. They can recommend the best type for you based on your personal circumstances and medical history.

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Development of the Fetus

It takes time for sperm to fertilize an egg and then travel down your fallopian tube and implant in your uterus. If implantation is successful, your body will begin producing hormones that support pregnancy. It will also stop your menstrual period.

The embryo then starts to grow and divide. Over the course of a week, it becomes a blastocyst, which is the stage that begins your pregnancy. At this point, the fetus is officially considered an embryo, even though healthcare professionals will still call it a zygote until he or she is born.

During this time, the fetus is developing its major organs and body systems. It is also putting on fat. The fetus is covered in a whitish coating called vernix, which acts as a barrier to protect it from the corrosive substances found in amniotic fluid.

After about a month, the fetus grows to the size of a black bean and begins to move around in your uterus. Some women start to feel these movements as early as 16 weeks, and those who have been pregnant before usually notice them earlier than those who are expecting for the first time. It is during this time that the fetus gets its assigned sex and begins growing its nails, hair and eyelashes. In addition, the fetus makes melanin, which is what gives it its skin color.

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