How soon will a pregnancy test read positive when you are pregnant? How many days after conception can you take a home pregnancy test? Can you have a negative pregnancy test and still be pregnant?
The key to answering these questions lies in understanding the timeframe of hCG production in very early pregnancy.
In this article:
- What is hCG?
- What week of pregnancy does hCG show up in the urine?
- HCG levels after conception
- How soon will a pregnancy test read positive?
- The accuracy of home pregnancy tests
- The best time to take a pregnancy test
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What is hCG?
HCG is the short name for the hormone human chorionic gonadotropin that’s produced in high levels during pregnancy. This hormone is often referred to as the “pregnancy hormone,” but it’s not unique to pregnancy only.
It’s normal for non-pregnant women (and even men!) to have some hCG in their system at all times at trace levels, generally under 5 mIU/mL (with the exception of non-pregnant menopausal and postmenopausal women who may have higher levels). [source:1,2,3] These normal low levels of hCG are not enough to be detected by a home pregnancy test.
When you are pregnant, your body produces more hCG, and those extra levels are what the test will pick up on.
What week of pregnancy does hCG show up in the urine?
Two things must happen before extra hCG is produced in pregnancy:
- conception (the sperm joins the egg)
- implantation (the fertilized egg implants in the uterus)
Over the next few days following ovulation, your hCG remains at the same preconception level even if conception has occurred. No extra hCG is made in pregnancy after conception until the fertilized egg travels down the fallopian tube towards the uterus where it attaches to the uterine lining, a process known as implantation.
Once implantation takes place, the cells that surround and nourish the developing embryo begin to secrete hCG which almost immediately makes it into the bloodstream and urine.
On average, implantation occurs about 8-10 days after ovulation, but it can take the developing embryo anywhere between 6-12 days to reach the uterus and attach to its lining. [source:1,2,3]
Example: from ovulation to implantation in a 28-day cycle:
HCG levels after conception
The hCG levels start off low but tend to rise rapidly in the first 4-6 weeks of pregnancy.
Early on in pregnancy, your hCG level is likely to double every 72 hours. [source]
That said, some studies show that when you are very early pregnant, meaning the embryo has just freshly implanted, hCG levels actually seem to increase at a much faster rate for a period of few days (read about how hCG rises after implantation in more detail, with figures from the studies shown).
The hCG increase rate slows down as the pregnancy progresses, and around the end of the first trimester the gradual upward trend reaches a peak. In the second trimester, hCG typically starts to drop and eventually levels off for the remainder of the pregnancy. [source]
Typical hCG levels by week of pregnancy:
| Weeks from last menstrual period | Range of hCG levels (in mIU/mL*) |
|---|---|
| 3 weeks LMP | 5 – 50 mIU/mL |
| 4 weeks LMP | 5 – 426 mIU/mL |
| 5 weeks LMP | 18 – 7,340 mIU/mL |
| 6 weeks LMP | 1,080 – 56,500 mIU/mL |
| 7-8 weeks LMP | 7,650 – 229,000 mIU/mL |
| 9-12 weeks LMP | 25,700 – 288,000 mIU/mL |
| 13-16 weeks LMP | 13,300 – 254,000 mIU/mL |
| 17-24 weeks LMP | 4,060 – 165,400 mIU/mL |
| 25-40 weeks LMP | 6,640 – 117,000 mIU/mL |
Pregnancy weeks are calculated from the first day of your last menstrual period. This would make the first day of your last period Pregnancy Day 1, making you about 4 weeks pregnant around the time of your missed period.
As you can see above, there is a huge variation in normal hCG levels throughout pregnancy. No magical number for hCG values exists for any specific day or week of pregnancy.
How soon will a pregnancy test read positive?
A home pregnancy test (HPT) checks for the presence of hCG in the urine. When you are pregnant, enough hCG must be excreted in the urine to meet the sensitivity threshold of your home pregnancy test.
How soon will a pregnancy test read positive will depend on the following factors:
- Timing of implantation:
HCG production in pregnancy starts with implantation (the developing fetus attaching inside the uterus). The average time for implantation to occur is 8-10 days after ovulation (6-12 days is the normal range).
- Rate of hCG increase:
In early pregnancy, hCG typically doubles every 2-3 days. The rate of hCG increase in very early pregnancy seems to be, however, much higher, doubling and even tripling from one day to the next in the immediate days following implantation.
- Pregnancy test sensitivity:
The kind of pregnancy test you use influences how soon you can see a positive result. The sensitivity of home pregnancy tests is indicated in mIU/mL – the lower the number, the lower the amount of hCG the test is able to detect and the sooner you will be able to test.
Most home pregnancy tests sold today have a sensitivity in the range of 20-25 mIU/mL. That means they are able to detect hCG in the urine if the levels are at least 20-25 mIU/mL at the time of testing. This is often enough for testing when your period is due or after a missed period, but not always enough for very early testing.
If you’re testing very early on – several days before your period is due, you’ll want to use a super sensitive pregnancy test like this one that’s able to detect hCG levels as low as approximately 6.3 mIU/mL hCG. [source] These are extremely low levels of hCG, just slightly above normal (non-pregnant) hCG levels. This way you can potentially get your first BFP as soon as 2-3 days after implantation, or approximately 10-11 days after ovulation, give or take.
Here are a few examples of how hCG levels rise in the first few days following implantation. You can see how much of a difference low hCG detection (7 mIU/mL vs. 20 mIU/mL) might make in very early pregnancy!
The accuracy of home pregnancy tests
I can’t speak for every pregnancy test manufacturer, but pregnancy tests made by well-known brands are generally accurate in detecting the stated hCG levels.
However, even with the most reputable pregnancy test you may run into one of the following scenarios:
- a false negative result
- a false positive result
A false negative result means that your pregnancy test is negative but you are indeed pregnant. This often happens when you test too early and don’t yet have enough hCG built up in your urine for the test to pick up on. Sometimes ovulation can be delayed which in turn delays implantation, or the implantation process can be slow – some embryos just take a bit more time even though they are on the right path. It’s also possible to have unusually low levels of hCG and a healthy pregnancy.
Related: Common & Totally Weird Very Early Pregnancy Symptoms
A false positive result means that you may get a positive result on your pregnancy test and NOT be pregnant. The most common reason for a false positive result on a pregnancy test is a very early miscarriage, also known as a “chemical pregnancy.” This happens when implantation is successful and the hCG numbers start off right but the pregnancy stops from progressing which triggers hCG to drop again – in the meantime, before hCG decreases back down to the original and non-detectable level, you might see a positive result on your pregnancy test.
The best time to take a pregnancy test
It is generally recommended to take a pregnancy test no sooner than around the time of your missed period. This eliminates a good portion of false positives as well as false negatives. But it’s close to impossible to follow this advice when you really really REAAALLY want to know, right?
My advice is – test when you want to test. Just know that it might be too early – even the most sensitive home pregnancy test on the market will not be accurate when taken too early.
Re-test in 1-2 days if your first result was negative but you think you might be pregnant. Given how quickly hCG levels tend to rise in early pregnancy, even 24 hours between testing can make a difference in finally getting a positive result. Many early pregnancy symptoms are attributed to the sharp increase in hCG levels in the early weeks of pregnancy, so if you start experiencing any odd symptoms here and there, it might be a good idea to take a pregnancy test!
The only guideline I would urge you to follow is that when testing before your period is due, it’s always best to use your first morning urine. It has the highest concentration of hCG for the day, and even a small spike in hCG can be the difference between a negative and positive result this early on in pregnancy.
If you are tempted to take a pregnancy test several days before your period is due, use one that’s designed to detect very low levels of hCG (like this one). After a missed period you can use a less sensitive pregnancy test as you will have had higher levels of hCG built up in your system.
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