In most normal pregnancies at an hCG level below 1,200 mIU/ml, the hCG usually doubles every 48-72 hours. At levels below 6,000 mIU/ml, the hCG levels normally increase by at least 60% every 2-3 days. Seebert et al reported in 2006 that a rise of at least 35% over 48 hours was proposed as the minimal rise consistent with a viable IUP. So it would be wrong to always assume the presence of a nonviable pregnancy even if the there is an hCG rise below 50% over 48 hours.
A rise of at least 35% over 48 hours can still be considered normal
Slow hCG Rise
Slower than expected hCG increases are more consistent with abnormal pregnancies such as miscarriages and ectopic pregnancies, and decreases are usually associated with failed pregnancies such as miscarriages or chemical pregnancies.
In many early pregnancies, the hCG level will double every 31 to 72 hours. As the pregnancy progresses, hCG levels rise and the doubling time increases.
After 6-7 weeks of the pregnancy, the best indication of a healthy pregnancy is a good fetal heartbeat on sonogram
. Blood hCG levels are not very helpful to test for the viability of the pregnancy if the hCG level is well over 6,000 and/or after 6-7 weeks of the pregnancy. Instead, a sonogram should be done to confirm the presence of a fetal heartbeat. Once a fetal heartbeat is seen, it is not recommended to check the pregnancy viability with hCG levels anymore.
NORMAL HCG DOUBLING TIMES
|HCG Level||DOUBLING TIME EXPECTED|
|Under 1,200 mIU/ml||Between 30 and 72 Hours|
|1200-6000 mIU/ml||Between 72 and 96 Hours|
|Over 6,000 mIU/ml||Over 96 Hours|
hCG levels rise during the first 6 to 10 weeks of pregnancy then decline slowly during the second and third trimesters.
As your pregnancy develops, the increase slows down significantly. Between 1,200 and 6,000 mIU/ml serum, the hCG usually takes about 72-96 hours to double, and above 6,000 mIU/ml, the hCG often takes over four or more days to double. It makes little sense to follow the hCG values above 6,000 mIU/ml as at this point the increase is normally slower and not related to how well the pregnancy is doing.
After two to three months, the increase will slow even further and eventually hCG levels may even decline before reaching a plateau for the duration of the pregnancy. Doctors will often use the quantitative blood test if they are closely monitoring the development of a pregnancy but above a level of about 6,000 mIU/ml that makes no sense because at this point a sonogram provides better information about the pregnancy.
One single hCG value does not tell you much about the viability of the pregnancy and there is a wide range of normal hCG levels in pregnancy. A normal hCG rise over several days prior to 6 weeks of the pregnancy usually indicates a viable pregnancy. In general, the best indication of a healthy pregnancy other than a normal rise of hCG is a good fetal heartbeat after 6-7 weeks.
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