Human chorionic gonadotropohin, hCG, is a hormone produced during pregnancy. Cells that form the placenta excrete hCG once an egg has been fertilized and implanted into the uterus. HCG levels double every 72 hours and peak between eight and 11 weeks gestation. Rising hCG levels are often associated with a healthy pregnancy; however, low hCG levels have also occurred in healthy pregnancies, according to Advanced Fertility. Many variables and conditions affect hCG levels.
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Miscalculated Gestational Age
The estimated date of birth is calculated based on your last menstrual period. If you have a history of irregular periods or are unsure of your last menstrual period prior to becoming pregnant, it may be harder to tell how far along you are in your pregnancy. If your pregnancy is very early or past 12 weeks gestation, hCG levels may be low, according to American Pregnancy Association. Ultrasound and repeat hCG levels may be needed to help correlate hCG levels and gestational age.
Miscarriage is the spontaneous loss of a pregnancy before 20 weeks gestation, according to the Mayo Clinic. Miscarriage may result in low hCG levels. A pregnancy that fails to develop a placenta may not excrete higher levels of hCG. Advanced Fertility states that hCG levels may be normal initially, then fail to rise in the event of a miscarriage.
A blighted ovum occurs when an egg is fertilized and attaches to the uterine wall, but fails to develop. Cells develop the gestational sac and may release hCG hormone, though the fertilized egg fails to develop further. A blighted ovum happens very early in pregnancy, usually before you know you are pregnant. A blood test to detect hCG may be performed if you suspect you are pregnant and may show elevated levels indicating pregnancy. However, additional hCG levels fail to rise or deplete.
Ectopic pregnancy occurs when a fertilized egg settles inside a fallopian tube, the tube that carries an egg from the ovary to the uterus, or outside the uterus. Ectopic pregnancy is a life-threatening condition, as it may cause fallopian tube rupture and bleeding. HCG levels may help differentiate a normal pregnancy from an ectopic pregnancy, states Medline Plus, as hCG levels from an ectopic pregnancy will remain low.