Every now and then, I’m asked to see a patient who is over 60 years old but who has somehow had a pregnancy test that just happened to be positive. How could this be? Should I call the tabloids and report that I have the world’s oldest pregnant woman in my office? Or is there another explanation?
What does the pregnancy test detect?
Pregnancy tests that use a woman’s blood detect a hormone called beta human chorionic gonadotropin (bhcg), a substance that is commonly produced by the placenta of a developing pregnancy. In a normal pregnancy, levels of this hormone in the blood will increase 60 percent to 100 percent every 48 hours until a stable, established level is reached (generally around 100,000 international units of bhcg per milliliter). A woman who is not pregnant should have a bhcg level of zero.
Abnormal bhcg levels
If a woman has a miscarriage, her bhcg level will gradually decrease from its elevated level until it returns to zero. If the bhcg is elevated but does not rise or fall properly, then the healthcare provider should become concerned about other possible conditions or adverse developments.
A pelvic ultrasound can help to evaluate for a properly developing pregnancy. It may also help detect ectopic or tubal pregnancies, which are often accompanied by elevated but slowly rising or plateaued bhcg levels.
If the ultrasound shows no pregnancy in the uterus or in the tubes, then the provider might also check the bhcg level again in 48 hours to help determine if the pregnancy is just too early to detect, or if the pregnancy is of concern for a possible ectopic pregnancy.
Abnormally high bhcg levels may also be concerning for or indicative of an abnormal pregnancy that can sometimes become cancerous (called a molar pregnancy). High levels of bhcg can even point to the presence of multiple fetuses.
What about the world’s oldest pregnant woman?
The woman in my office wasn’t really pregnant at all, but she did have a positive bhcg level. This situation does arise and, as I said, it can be worrisome for certain types of cancer. Certain types of ovarian cancer may elevate bhcg levels, but the cancer doesn't have to be from some part of the female reproductive anatomy at all. Other non-gynecologic cancers that can occasionally produce bhcg include cancers of the lungs, liver, breast, bladder, and gastrointestinal tract.
Low-level bhcg levels
If such malignancies as these are not found in a non-pregnant woman whose body is producing bhcg, and the bhcg level is fairly low and stable, then it’s likely that the slight elevation is merely normal. The test itself uses an assay that will detect antibodies that some women may have developed, and then will report this as a positive result. So, if a woman has these antibodies, she may have a low-level, positive test.
What if you have a bhcg test and it’s positive?
If it’s not clear that you are pregnant, then the best way to evaluate such a result is to repeat the test in 48 hours.
If the levels are increasing 60 percent to 100 percent in 48 hours, then you probably have a normal pregnancy inside the uterus.
If the levels are elevated but not rising properly, they may indicate an ectopic pregnancy, or a pregnancy that isn’t developing properly.
If the levels are extremely high, you may have a more serious condition, like a molar pregnancy—or you might just have triplets!
If the level is elevated and it’s clear that you are not pregnant, then the concern is for a malignancy.
If the possibility of a malignancy can be eliminated, and if the level is low and stable, then your body may just have antibodies that cross with the test! Your healthcare provider can help you get to the bottom of the matter and get the right care that you need.