Pregnancy levels are measured by testing blood or urine levels of beta hCG, or human chorionic gonadotropin, which is produced by cells that form the placenta. Only blood tests give an exact reading of hCG levels, and are often done serially to ensure that hCG levels (also called beta levels) are rising appropriately.
Normal Levels
HCG is normally not detectable in the blood until 10 or 11 days after ovulation at the earliest. Levels over 5 milli-International Units per milliliter (mIU/ml) are considered positive for pregnancy. In 85 percent of cases, hCG levels double every 48 to 72 in normal pregnancy, the American Pregnancy Association explains. Doubling every two to three days is common only through week 6 of pregnancy.
HCG levels level off around 8 to 10 weeks of pregnancy, so levels that don't double after that point don't indicate any problem with the pregnancy, Advanced Fertility Center of Chicago reassures. Average hCG levels around the time of a missed period are around 50 mIU/ml, but many perfectly normal pregnancies start out with higher or lower levels.
Slowly Rising Levels
Abnormally slow rises in beta hCG levels are usually caused by problems with the pregnancy. An abnormal embryo that's destined to miscarry often produces abnormally low concentrations of hCG. Ectopic pregnancies, where an embryo grows in to the fallopian tube or other area outside the uterus, can also cause a slowly rising beta level.
If the hCG level fails to rise appropriately for one or two tests, then rises again, a twin may have been lost while the other embryo continues to grow. An hCG level that doesn't change at all, or that begins to drop, is usually a sign of chemical pregnancy, where the embryo implanted but then stopped growing very early in pregnancy.
Rapdily Rising Levels
Molar pregnancies, where the fetus doesn't grow but placental tissue does, may cause abnormally high hCG levels, Tulane University School of Medicine states. Choriocarcinoma, a cancer arising from a molar pregnancy, also results in rapidly rising or persistently elevated hCG levels. Higher than expected levels of hCG may be seen in genetically abnormal pregnancies, such as those where the fetus has Down syndrome, according to the National Institutes of Health. An hCG level that's rising faster than expected may also occur in multiple pregnancies.
Further Testing
An abnormally rising hCG level may merit additional testing. Vaginal ultrasound can detect the presence of multiples. The presence of a growing fetus with a heartbeat over 90 beats per minute by the seventh week of pregnancy is a reassuring sign that the fetus is developing normally, the American Pregnancy Association states.
Treatment
Any deviation from the norm is concerning to pregnant women. Unfortunately, nothing can be done to change an inappropriately rising hCG level except to check the pregnancy by doing an ultrasound.
References
- American Pregnancy Association: Human Chorionic Gonadotropin (hCG): The Pregnancy Hormone
- Advanced Fertility Center of Chicago: Early Pregnancy - Including HCG levels and ultrasound findings
- Western Michigan University Sindecuse Health Center: Free Pregnancy Testing
- Tulane University School of Medicine: Gestational Tumors
- American Pregnancy Association: Concerns Regarding Early Fetal Development
