Human chorionic gonadotropin, or hCG, is a hormone produced during pregnancy. It is made by cells formed in the placenta, which nourishes the egg after it has been fertilized and becomes attached to the uterine wall. hCG can be detected in urine or blood tests. Doctors may test hCG levels to confirm pregnancy or monitor the health of the pregnancy.
Women wonder when is the best time of day to test urine hCG levels. This matters because hCG levels rise quickly early in pregnancy and testing when hCG is most concentrated improves chances of getting an accurate positive result. Here is a look at how hCG urine levels fluctuate during the day and when they tend to be highest.
When hCG Starts Rising in Early Pregnancy
hCG is made shortly after a fertilized egg implants in the uterus. It serves to signal the ovaries to maintain production of estrogen and progesterone which support the uterine lining where the embryo will develop.
Doctors measure hCG in milliunits per milliliter, or mIU/mL. hCG usually appears in the blood around 10 days after ovulation/fertilization and in the urine around 14 days after. Levels double every 1.5 to 3 days for the first several weeks. Concentrations peak around weeks 10-12 of pregnancy.
During the first few days after implantation, hCG levels are very low, often below the threshold of sensitivity for urine and blood tests. Levels only become detectable around the time of the first missed period. However, there can be a wide variation in how quickly hCG rises and when it passes the detection threshold.
When During the Day Are hCG Levels Highest?
hCG is metabolized and excreted by the body throughout the day. This means levels can fluctuate based on how diluted urine is. Here are some patterns that influence hCG urine test results:
– First morning urine generally contains the most concentrated levels of hCG because it has built up overnight without being diluted by drinking fluids.
– Levels fall throughout the morning as fluid intake increases and urine dilutes the hCG.
– Concentrations rise again in early afternoon as the kidneys filter waste.
– Late afternoon or evening urine is often more dilute after drinking water throughout the day.
Typical hCG Ranges Throughout Day:
|Time of Day||Typical hCG Range (mIU/mL)*|
*Ranges are approximate for urine tests in early pregnancy
As you can see, hCG levels can vary widely throughout the day. Values also depend on the exact number of days past ovulation and embryo implantation. During early pregnancy, it’s best to test first morning urine. This gives the highest hCG concentration and lowest chance for a false negative result.
When to Test Morning vs Afternoon/Evening
Here are some guidelines on when to test morning vs afternoon/evening urine based on where you are in pregnancy:
Very Early Pregnancy
If you are before your missed period or within just a few days after, test first morning urine. At this very early stage, hCG is still low and you want the most concentrated sample. Stick to first morning urine until you get a positive test result.
Around Week 4-6
Once you get a positive pregnancy test, you can be less stringent about testing first morning urine. In weeks 4-6, hCG is high enough that it should be detected even in afternoon/evening urine. You may test any time of day and see darker test lines in morning urine.
Beyond Week 6
After week 6, hCG levels plateau. At-home urine test lines will appear equally dark any time of day. You may test with any urine. Quantitive hCG blood tests are more precise if your doctor wants to monitor levels.
How Hydration Affects hCG Levels
Drinking more or less fluid can make hCG urine levels vary widely throughout the day. Here’s how hydration status influences test results:
If you drink plenty of fluids overnight and in the morning, your urine will be more dilute. This may lower apparent hCG levels and potentially delay getting a positive pregnancy test.
If you are dehydrated and produce only small amounts of concentrated urine, hCG levels will appear higher. This could cause tests to turn positive slightly sooner. But dehydration is not recommended.
It’s best to be normally hydrated when taking an hCG urine test. Avoid drinking large amounts of fluid before testing so urine is not overly diluted. But do not restrict fluids to the point of dehydration. Staying well hydrated is important for mom and baby!
How Sensitive Are hCG Urine Tests?
Home pregnancy tests detect hCG by binding to the hormone in urine. Test sensitivity is measured by the lowest hCG concentration the test becomes positive. Most kits today can detect levels of 25-50 mIU/mL or less. Early pregnancy tests are optimized to turn positive very soon after hCG becomes elevated.
Factors influencing sensitivity:
- Test brand – some kits are more sensitive than others
- Testing with first morning urine vs. later in day
- Following test instructions properly
To maximize chances of an accurate early positive, select a test with sensitivity of 25 mIU/mL or use first morning urine. Retest 48 hours later if initial result is negative but pregnancy is suspected.
hCG Test Results Interpretation
Remember, hCG levels vary widely normal in early pregnancy. Here is how to interpret test results:
A negative test but no period likely means you tested too early and hCG hasn’t reached the detection threshold. Retest in a few days using first morning urine. If pregnancy is still suspected, follow up with a quantitative blood test which is more sensitive than urine tests.
A positive test result almost certainly indicates pregnancy. False positive urine test results are extremely rare. Confirm with your doctor and follow hCG levels until the expected 6-7 week ultrasound.
A faint positive line indicates hCG levels are near the test detection threshold. Retest with a quantitative blood test to be sure. The line should darken on repeat testing 48 hours later.
No Line Progression
If test lines do not darken over 48-72 hours it may indicate a problem with the pregnancy. Contact your doctor for quantitative hCG blood tests and an ultrasound.
– First morning urine contains the most concentrated hCG levels and is recommended for early pregnancy testing
– Drink normally before testing and use an early detection test for accurate results
– Retest within 48 hours if initial urine test is negative but pregnancy is suspected
– Contact your doctor for quantitative hCG blood test and ultrasound if there are concerns about test results
Urine hCG levels fluctuate during the day with the highest concentrations in first morning urine. Testing first thing when waking up gives the earliest positive pregnancy test results. Use first morning urine until hCG levels are well above the test detection threshold around 4-6 weeks gestation. After this point, hCG levels plateau and urine can be tested any time of day. Stay well hydrated for healthy pregnancy as overly dilute or concentrated urine can affect test accuracy. Home pregnancy tests today are highly sensitive and accurate when used as directed with first morning or afternoon urine. Always follow up unclear or unexpected test results with your doctor.