How Long After Implantation Does hCG Rise?

By Dr. Kenosha Gleaton, OBGYN

Understanding Implantation and Its Role in Pregnancy

Implantation marks the beginning of pregnancy. After implantation, there are many processes that will follow in order to support a healthy pregnancy. Hormones will begin to change, cells divide rapidly, and the body adjusts accordingly. Let’s talk a bit more about what implantation is and when it occurs. 

What Is Implantation?

Implantation is defined as the process by which the embryo attaches to the endometrial surface (lining) of the uterus. [1] Let’s take a step back and go over all the moving parts that contribute to pregnancy. The three key things that are responsible for gestation include an egg, sperm, and a pathway for the two to meet. Ovulation is the monthly release of an egg and the days leading up to ovulation are known as the fertile window. If two people have unprotected heterosexual sex during the fertile window, the chances are much higher that sperm and egg will meet and fertilization will occur. After fertilization, the egg (now referred to as a zygote) will travel down the fallopian tube and into the uterus, where implantation can take place. [2] Pregnancy will not progress and the embryo will not continue to develop if implantation doesn’t occur. In some cases, a fertilized egg will just be passed during the next menstrual period. [2] However, if the embryo does attach itself to the lining of the uterus, cells will continue to divide and the body will begin releasing the necessary hormones to prevent menstruation and support gestation. [1-2] 

When Does Implantation Typically Occur?

Implantation typically occurs about one week after fertilization, or about 5-10 days after a positive ovulation test/luteinizing hormone surge. [1] There is a relatively short window of time when implantation can occur, which is approximately days 16-22 of the menstrual cycle. The specific day that implantation occurs can vary depending on how long someone’s menstrual cycle is. Learn more in my article, Can You Get Pregnant a Week After Ovulation?

Unveiling the hCG Hormone

Ever wonder how a pregnancy test actually works? What is it in your urine that triggers a positive result? Let’s talk about the pregnancy hormone, also known as hCG. 

What is hCG?

Human chorionic gonadotropin (hCG), is a hormone that is found in both blood and urine during pregnancy. [3] The body begins to produce hCG after implantation has occurred and the placenta begins to grow. The presence of this hormone signals the body to produce progesterone, which is vital for maintaining pregnancy. 

How is hCG Measured?

There are two ways to measure hCG: urine testing and blood serum testing. Typical home pregnancy tests or pregnancy test strips are a great example of urine hCG testing. Some pregnancy tests are more sensitive than others, meaning they can detect lower levels of hCG, potentially leading to a positive test result up to five days before an expected period. Blood tests can be done by a provider but aren’t always necessary if an ultrasound and urine pregnancy test both indicate a pregnancy. [3] However, blood tests can tell providers how much hCG is present, which can be helpful in certain cases, such as monitoring fertility treatment outcomes, identifying any problems, etc. Blood tests are also more sensitive than urine tests and can detect pregnancy with a smaller amount of hCG. [3] 

The Journey of hCG Levels Post Implantation

Measuring hCG levels can tell your provider a lot about your pregnancy and health. Here’s what you need to know. 

Initial Rise in hCG Levels

As mentioned already, hCG levels begin to rise as soon as implantation occurs. This increase in hCG happens quickly during early pregnancy, doubling every 24 hours for about 8 weeks. [4] HCG levels are at their highest around 10 weeks of gestation, decrease until about the 16th week of gestation, and then remain fairly constant throughout the rest of pregnancy. [4] 

Tracking hCG Levels

Seeing hCG levels rise consistently during the first trimester is a good indicator of a healthy pregnancy. If levels plateau before the eighth week of pregnancy or drop off, it may be a sign of a miscarriage, ectopic pregnancy, or another complication. [3-4] Generally, hCG levels won’t be tested more than once or twice during pregnancy unless your provider has reason to test more often. [3] 

Symptoms Associated with Rising hCG Levels

The quick rise in hormones has been theorized as the cause of many early pregnancy symptoms. Not only is hCG rising, but progesterone levels are also increasing during early pregnancy. Some symptoms associated with early pregnancy and potentially a rise in hCG include [5]:

• Nausea and vomiting (get morning sickness relief here) 
• Fatigue
• Sore breasts
• A missed period
• Headaches or dizziness
• Slight cramping
• Bloating
• Spotting (read can implantation bleeding be heavy?)

Taking a Pregnancy Test: Timing and Considerations

Taking a pregnancy test can lead to a range of emotions from frustration to excitement. Let’s review when the ideal time to take a pregnancy test is.  

When to Take a Pregnancy Test?

When you should take a pregnancy test may differ depending on a few factors. Are you actively trying to conceive (TTC)? Have you been tracking ovulation? Are you experiencing any symptoms? In general, it’s good to know if you’re pregnant as early as possible so you can get prenatal care quickly. However, if you’re actively TTC and you know that you ovulated within the past few days, chances are that it’s too early for a pregnancy test to give you an accurate result. HCG levels will begin to rise soon after implantation occurs, which is about 5-10 days after ovulation. [1] Even the most sensitive pregnancy tests will only be able to detect hCG levels a few days before a missed period. So if you’re very eager, you can try testing a few days before your next expected period, but don’t be discouraged if you aren’t seeing a positive result right away. If you have concerns or questions about testing for pregnancy, be sure to speak to your healthcare provider. If you are actively trying to conceive, it’s highly recommended that you take a prenatal vitamin to support early fetal development! 

Factors Influencing hCG Levels Post Implantation

In most circumstances, hCG levels will rise quickly and stay within a certain threshold during pregnancy. Let’s review some conditions or circumstances that can impact hCG levels post-implantation. 

Concerns with Slow-Rising hCG Levels

What do low hCG levels mean? There are a few reasons you may have low hCG levels, including [3-4]:

• Miscarriage
• Ectopic pregnancy
• Miscalculation of gestational age
• Blighted ovum (a growing gestational sac and placenta without an embryo) 

High hCG Levels: Causes and Implications

Even if it doesn’t sound like it, a higher-than-normal hCG level may also indicate a potential issue. In some cases, high hCG levels indicate a multiple gestation (twins, triplets, or more). High levels of hCG may also indicate [3-4]:

• A molar pregnancy
• Miscalculation of gestational age
• Abnormal growths

Keep in mind that most people don’t actually know what their hCG levels are, and a urine pregnancy test will only signal that there is some level of hCG in your urine. Your provider may measure your hCG levels if you have a history of infertility, are going through fertility treatments, or if your initial levels seemed abnormal. Speak to your provider if you have concerns or questions about testing for pregnancy. 

Natalist: Your Companion in the Fertility Journey

To recap: hCG begins to rise as soon as implantation occurs, which happens about 5-10 days after ovulation. Most highly sensitive or early-result pregnancy tests will be able to detect hCG levels a few days before your next expected period. 

Natalist is proudly run by a team of moms and doctors who have lived through the many highs and lows of fertility, pregnancy, and postpartum. We know that everyone’s journey is different but equally deserving of high-quality care and products. Get the answers you need with Natalist tests, and support your TTC journey with fertility and pregnancy supplements. 

References:

1. Kim SM, Kim JS. A Review of Mechanisms of Implantation. Dev Reprod. 2017;21(4):351-359. doi:10.12717/DR.2017.21.4.351
2. Conception. Cleveland Clinic. September 2022. https://my.clevelandclinic.org/health/articles/11585-conception
3. Human Chorionic Gonadotropin. Cleveland Clinic. March 2022. https://my.clevelandclinic.org/health/articles/11585-conception
4. Betz D, Fane K. Human Chorionic Gonadotropin. [Updated 2023 Aug 14]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK532950/
5. Am I Pregnant? Cleveland Clinic. July 2022. https://my.clevelandclinic.org/health/articles/9709-pregnancy-am-i-pregnant