3 weeks pregnant: Your guide to this week of your first trimester

    Updated 29 June 2023 |
    Published 24 February 2019
    Fact Checked
    Reviewed by Dr. Nazaneen Homaifar, Obstetrician and gynecologist, Inova Health System, Washington, DC, US
    Written by Kate Hollowood
    Edited by Sarah Biddlecombe
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    From fertilization to implantation, here’s the lowdown on being 3 weeks pregnant.

    Whether you’re trying for a baby or not, it’s natural to be full of questions during the early weeks of pregnancy. At 3 weeks pregnant, you’re probably wondering whether you can get pregnancy symptoms before a missed period — or whether it’s worth taking a pregnancy test yet. 

    The 3-week mark is an exciting and important time in your pregnancy because this is when fertilization and implantation take place. Keep reading to learn more about what’s going on in your body during this special week from a Flo expert, as well as how to take care of yourself and your potential future baby. 

    Your baby at 3 weeks pregnant

    Cells dividing

    Before we get started, let’s take a quick math lesson. The weeks of your pregnancy are counted from the first day of your last period (rather than the day of conception), which can be confusing. To recap your journey so far, 1 week pregnant marks the beginning of your new menstrual cycle. Then at 2 weeks pregnant, your body is preparing for ovulation and the release of an egg. At 3 weeks pregnant, a champion sperm will fertilize your egg, before this fertilized egg implants itself into your uterus. Don’t worry if counting the weeks in this way feels strange at first, as it will start to feel more natural as the weeks go on. 

    So, while there isn’t a baby there just yet, 3 weeks pregnant is when fertilization happens. Your egg gets fertilized by a sperm within 24 hours of ovulation. This single cell then divides into multiple cells over the next few days.

    Implantation

    Next comes the big moment: Between days 20 and 24 of your cycle, or 6–10 days after ovulation, your fertilized egg will implant itself into your uterus, and you will officially become pregnant. Once the fertilized egg (which at this stage is called a blastocyst) has fully embedded into the uterus, it will start receiving nourishment from your body.

    Your body at 3 weeks pregnant

    Implantation bleeding

    You might be wondering whether there are any signs and symptoms that indicate when implantation has happened. And there are! Some women experience implantation bleeding as the fertilized egg embeds itself into the uterus. However, only 25% of pregnant women will experience this, so if you don’t, then fear not — that’s totally normal. 

    This type of bleeding can easily be confused with a period, so what are some of the key differences to look out for? Well, implantation bleeding will be noticeably lighter and tends to only last up to 2 days. “Implantation bleeding is very light, usually pink or light brown in color, and typically described as streaks or a small amount of spotting,” explains Dr. Jenna Flanagan, academic generalist obstetrician and gynecologist, Beth Israel Deaconess Medical Center, Massachusetts, US. “It does not become bright red, heavy, or contain clots. This can mimic the beginning of a menstrual cycle. However, if the bleeding is from a period, it is often constant and begins to become darker, heavier, and more red over the next 24 hours.”

    And when might you expect to see implantation bleeding? Dr. Flanagan explains, “Some people report spotting or light bleeding approximately 7 to 14 days after ovulation has occurred, therefore around week 3 to 4,” she says. 

    It’s too early for pregnancy symptoms 

    It’s too early for any pregnancy symptoms at 3 weeks. In fact, many people feel the same as normal at this stage. It can be reassuring to know that pregnancy symptoms don’t usually start until you’re around 4 to 6 weeks pregnant. Some of the early signs and symptoms of pregnancy to look out for in the future include: 

    • A missed period
    • Tender breasts
    • Fatigue
    • Gas and bloating

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    Your questions answered

    What does a 3-week pregnancy look like?

    As fertilization and implantation usually happen at this stage, it’s still too soon for even very early pregnancy symptoms. So rest assured that if you feel no different than usual, it’s not a sign that anything is wrong with you or your future baby. As we’ve seen, you might experience implantation bleeding, but not every woman does. 

    What should I avoid at 3 weeks pregnant?

    Maintaining a healthy lifestyle is always a good idea when you’re trying to conceive, but at 3 weeks pregnant, there isn’t anything specific to avoid. “There is no data to support avoiding anything in particular during implantation,” assures Dr. Flanagan. “However, if you are actively trying to conceive, it would be prudent to discontinue alcohol consumption after ovulation. During the third and fourth week, the pregnancy implants and develops a blood flow connection to the uterus, meaning it can be exposed to certain medications, drugs, and alcohol.”

    Alongside cutting out alcohol, you should avoid certain foods during pregnancy to reduce the risk of bacterial infections. Some foods to avoid during pregnancy include certain cheeses, like brie and feta, raw and undercooked meat and eggs, and seafood high in mercury. You can read more about this in our pregnancy diet guide, but always be sure to speak to your doctor if you have any questions or concerns.

    Can you get a positive pregnancy test at 3 weeks?

    Even though you may now be officially pregnant, it’s very unlikely that you’d get a positive result from a home pregnancy test at 3 weeks. So hold on for a little longer if you can! 

    Here’s why: Pregnancy tests work by detecting the pregnancy hormone called human chorionic gonadotropin (hCG) once it reaches a certain threshold. Your body doesn’t start producing this hormone until around 6 days after fertilization. It then rises quickly, with the amount of the hormone in the urine or blood doubling every 2 to 3 days. However, there is also evidence to suggest that the rate of hCG increase can be more variable than this and actually differ from person to person. So for the most accurate result, it’s best to wait another week or so until after the first day of a missed period

    Interestingly, if you conceive after ovulation, your basal body temperature (BBT) will stay high, rather than decrease as it usually would. BBT is your body’s temperature at complete rest, and it rises slightly after ovulation has happened. If you’re measuring your temperature each morning to figure out when you ovulate, your data may just provide an early sign of pregnancy, too. 

    However, BBT tracking may be tricky given that body temperature can be affected by many factors, including sleep, alcohol use, or even a fever. It is also not considered a reliable way to detect pregnancy, so you should always do a pregnancy test if you think you might be pregnant.  

    Your 3 weeks pregnant checklist

    It’s too early for a pregnancy test

    As we’ve seen, it’s still too early to take a home pregnancy test if you’re looking to get the most accurate result

    However, Dr. Flanagan explains that blood tests can detect pregnancies earlier than urine tests. She says, “The serum or blood test is much more sensitive and can detect hCG levels down to 5 mIU/mL, but the urine pregnancy test does not show positive until the hCG level in the blood is between 30 and 50 mIU/mL in the most sensitive tests.” 

    As most home pregnancy tests are urine tests, it’s better to hold off testing for now. “It is advised to wait until around week 4, or your first missed period, to ensure that the level of hCG in the urine is sufficient to be detected,” says Dr. Flanagan. “This will also limit your chances of getting a false-negative pregnancy test (meaning the test was taken too early, and there wasn’t a high enough level of hCG to be detected in the urine, but you are actually pregnant).” 

    When to consult a doctor at 3 weeks pregnant

    You don’t need to get in touch with your doctor until you’ve had a positive pregnancy test. However, if you’re trying for a baby and have any questions or concerns about conceiving, there’s no harm in getting in touch with them for some advice and reassurance. 

    3 weeks pregnant: The takeaway 

    While there is lots happening in your body this week, there’s a good chance you won’t even notice! If you’re trying for a baby, it can be reassuring to know that it’s common to feel no different from usual at this stage. As difficult as it can be sometimes, try to relax and know that you should be able to get a reliable answer from a pregnancy test soon. 

    References

    “Am I Pregnant?” Cleveland Clinic, my.clevelandclinic.org/health/articles/9709-pregnancy-am-i-pregnant. Accessed 24 May 2023.

    Barnhart, Kurt T., et al. “Differences in Serum Human Chorionic Gonadotropin Rise in Early Pregnancy by Race and Value at Presentation.” Obstetrics and Gynecology, vol. 128, no. 3, Sep. 2016, pp. 504–11.

    “Basal Body Temperature.” Cleveland Clinic, my.clevelandclinic.org/health/treatments/21065-basal-body-temperature. Accessed 24 May 2023.

    “Basal Body Temperature for Natural Family Planning.” Mayo Clinic, 10 Feb. 2023, www.mayoclinic.org/tests-procedures/basal-body-temperature/about/pac-20393026.

    “Blastocyst.” Mayo Clinic, 9 Sep. 2021, www.mayoclinic.org/tests-procedures/in-vitro-fertilization/multimedia/blastocyst/img-20008646.

    “Conception.” Cleveland Clinic, my.clevelandclinic.org/health/articles/11585-conception. Accessed 24 May 2023.

    “Do You Know Which Foods to Avoid When You’re Pregnant?” Mayo Clinic, 22 Jan. 2022, www.mayoclinic.org/healthy-lifestyle/pregnancy-week-by-week/in-depth/pregnancy-nutrition/art-20043844.

    “Doing a Pregnancy Test.” NHS, www.nhs.uk/pregnancy/trying-for-a-baby/doing-a-pregnancy-test/. Accessed 24 May 2023.

    “Fetal Development.” Cleveland Clinic, my.clevelandclinic.org/health/articles/7247-fetal-development-stages-of-growth. Accessed 24 May 2023.

    “Fetal Development: What Happens during the 1st Trimester?” Mayo Clinic, 3 June 2022, www.mayoclinic.org/healthy-lifestyle/pregnancy-week-by-week/in-depth/prenatal-care/art-20045302.

    Grant, Azure, and Benjamin Smarr. “Feasibility of Continuous Distal Body Temperature for Passive, Early Pregnancy Detection.” bioRxiv, 21 Aug. 2021, https://doi.org/10.1101/2021.08.19.21262306.

    “How Your Fetus Grows during Pregnancy.” The American College of Obstetricians and Gynecologists, Aug. 2020, www.acog.org/womens-health/faqs/how-your-fetus-grows-during-pregnancy

    “Home Pregnancy Tests: Can You Trust the Results?” Mayo Clinic, 23 Dec. 2022, www.mayoclinic.org/healthy-lifestyle/getting-pregnant/in-depth/home-pregnancy-tests/art-20047940.

    “Implantation Bleeding.” Cleveland Clinic, my.clevelandclinic.org/health/symptoms/24536-implantation-bleeding. Accessed 24 May 2023.

    “Pregnancy Test: When to Take, Types & Accuracy.” Cleveland Clinic, my.clevelandclinic.org/health/articles/9703-pregnancy-tests. Accessed 24 May 2023.

    “Signs and Symptoms of Pregnancy.” NHS, www.nhs.uk/pregnancy/trying-for-a-baby/signs-and-symptoms-of-pregnancy/. Accessed 24 May 2023.

    Su, Ren-Wei, and Asgerally T. Fazleabas. “Implantation and Establishment of Pregnancy in Human and Nonhuman Primates.” Advances in Anatomy, Embryology, and Cell Biology, vol. 216, 2015, pp. 189–213.

    “Symptoms of Pregnancy: What Happens First.” Mayo Clinic, 3 Dec. 2021, www.mayoclinic.org/healthy-lifestyle/getting-pregnant/in-depth/symptoms-of-pregnancy/art-20043853.

    “The Top 6 Pregnancy Questions I Hear from First-Time Moms.” The American College of Obstetricians and Gynecologists, Apr. 2022, www.acog.org/womens-health/experts-and-stories/the-latest/the-top-6-pregnancy-questions-i-hear-from-first-time-moms

    History of updates

    Current version (29 June 2023)

    Reviewed by Dr. Nazaneen Homaifar, Obstetrician and gynecologist, Inova Health System, Washington, DC, US
    Written by Kate Hollowood
    Edited by Sarah Biddlecombe

    Published (24 February 2019)

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