Several times a week in my practice, and in my Internet roles at the WebMD Fertility Center and the Pregnancy Board at WebMD, I have the opportunity to deal with early pregnancies and patients who want or need to know if a pregnancy is progressing normally (or not). In my short twenty years in practice, technological advances have come about that allow careful monitoring of pregnancies in the first half of the first trimester. These modalities have the potential to determine the viability of a gestation before any negative sign or symptom develops, and, if used properly they can prevent dangerous complications or reassure patients during uncertain times. But along with the technology and the good comes misuse and inappropriate interpretation that can do a lot of damage and cause a lot of worry in many instances.
There are several reasons to monitor pregnancies during the first few weeks after conception. These include:
- bleeding in early pregnancy
- possible ectopic pregnancy
- recurrent miscarriage
- patient anxiety due to previous pregancy loss
It’s important to note that there is no intervention available today to a woman who is already pregnant that will influence the rate of early pregnancy loss. Monitoring pregnancies may reduce anxiety, prevent rupture of ectopic pregnancy, and avoid the unease in waiting for a miscarriage to declare itself, but it cannot provide information that will affect the pregnancy’s prognosis.
The human pregnancy hormone, human chorionic gonadotropin (HCG) is first found in a pregnant woman’s blood as early as 7 to 8 days after conception. As a pregnancy grows, HCG increases. Measurements of HCG levels can be useful during the early weeks before the fetal heartbeat is seen on ultrasound, usually around 6-7 weeks after last menstrual period, or 4-5 weeks after conception.
A single HCG value doesn’t give enough information about the health or viability of the pregnancy. Within the first 2-4 weeks after fertilization, HCG usually doubles every 48-72 hours. That usually corresponds to HCG levels below 1200 IU. From 1200-6000, the HCG usually takes 72-96 hours to double. Above 6000 IU, the hCG often takes over four days to double. So, the rate of increase in HCG levels normally varies as a pregnancy progresses. Normal HCG values vary up to 20 times between different pregnancies, however, and an HCG that does not double every two to three days does not necessarily indicate a problem with the pregnancy. Some normal pregnancies will have quite low levels of HCG, and result in perfect babies.
Pregnancies that will miscarry and ectopic (tubal) pregnancies are likely to show lower levels and slower rises, but often have normal levels initially. Sometimes it takes three or more HCG levels at least 48 hours apart to get an idea how a pregnancy is progressing.
Once the HCG levels are above 1000-1500 IU, vaginal sonography usually identifies the presence of an intrauterine pregnancy. At that point an ectopic pregnancy is effectively ruled out. Once the pregnancy is visible on ultrasound, further HCG testing is less reliable than ultrasound for monitoring a pregnancy, as the variations in HCG levels are frequently misleading and cause unnecessary worry. Since normal levels of HCG can vary tremendously, after 5-6 weeks of pregnancy, sonogram findings are much more predictive of pregnancy outcome than are HCG levels. Once the gestational sac is seen, most doctors will monitor with ultrasounds rather than drawing HCG. Subsequent monitoring with ultrasound should reveal normal growth of the gestational sac, and the development of a fetal heartbeat by 6 to 7 weeks’ gestation (6-7 weeks after LMP). Once fetal activity has been detected by ultrasound, the chance of miscarriage is usually less than 10%.
My general recommendations regarding the appropriate use of HCG testing are summarized below. By following these guidelines, unnecessary testing that might lead to needless worry might be avoided, and just the right information will be obtained.
- If you’re pain-free and you’re not bleeding and you’re at low-risk for an ectopic pregnancy, try to avoid the temptation to monitor HCG levels. Generally no bleeding (no news) is good news. The pregnancy is on autopilot, and there’s little you can do to influence it at this stage. Try to relax and wait and see.
- IF HCG monitoring is indicated, try not to read too much into the absolute numbers and rates of increase of the HCG levels. Trust your doctor’s knowledge and experience to tell you if and when to repeat the tests, when and how to react to the numbers, and when to have an ultrasound. I can’t tell you how many patients I’ve had who convinced themselves that their pregnancy was doomed based on inappropriate interpretation of HCG levels, only to discover that everything is fine when an appropriately timed ultrasound is performed.
- Once an intrauterine pregnancy is visible on ultrasound, do not put any faith in HCG measurements. Frequently pregnancies and their HCG levels don’t fit the mold, and the numbers don’t increase the way they “ought” to. Rely on time, and predictable ultrasound changes to determine pregnancy viability.
- Remember that positive thinking and trust in the process are important in shaping your experience and add good karma to our world!