Progesterone During Pregnancy

• The importance of progesterone to your pregnancy helps explain the need for hCG production. During the second half of your menstrual cycle, high levels of progesterone keep you from having a menstrual period and help prepare your uterine lining for successful implantation of the fertilized egg. Once you get pregnant, progesterone helps prepare your breasts to produce milk for your baby following birth. Progesterone fulfills other important tasks during pregnancy, including lowering the levels of prostaglandins in your body and inhibiting uterine contractions. According to Robert Creasy, MD, Professor Emeritus in the Department of Obstetrics, Gynecology and Reproductive Sciences at the University of Texas Medical School at Houston, inadequate levels of progesterone during early gestation will result in the loss of your pregnancy.
  
  

The Corpus Luteum and Hormones

• During ovulation, a follicle in one of your ovaries releases a mature egg that travels down your fallopian tube to be fertilized. This follicle develops into the corpus luteum, which produces high levels of estrogen and progesterone, two hormones that are essential to maintaining your pregnancy. If sperm does not fertilize the egg, then your body has no need for the high levels of estrogen and progesterone; the corpus luteum stops production of these two hormones and degenerates, causing your body to go through a menstrual period.
  
  

HCG Production

• If sperm fertilizes the egg, the egg travels into your uterus (attaching to the uterine lining), and the cells around it (which eventually form the placenta) begin to produce hCG. The embryo's production of hCG sends a signal to the corpus luteum to continue producing progesterone in order to maintain the pregnancy. Creasy states that hCG extends the life of the corpus luteum until the placenta has developed to the point that it can produce progesterone itself. Typically, this shift of progesterone production from the corpus luteum to the placenta takes place around 10 weeks of pregnancy, so hCG plays an essential role during that time period in keeping your unborn baby alive.
  
  

HCG Levels

• Once the embryo begins producing hCG, the levels of this hormone in your body rise regularly. The American Pregnancy Association states that a blood test can first detect levels of hCG about 11 days following conception; a urine test can detect hCG approximately 12 to 14 days following conception. In most pregnancies, hCG levels double approximately every two to three days, peaking some time between the eighth and 11th week of pregnancy. Your hCG levels will then lower and level off for the rest of your pregnancy.
  
  

Problems with hCG Production

• HCG levels typically rise at certain rates during early pregnancy. If your obstetrician or midwife notes that your hCG levels are abnormal, she will usually check your levels several times to determine the health of your pregnancy. According to the American Pregnancy Association, high levels of hCG in your blood may indicate a molar pregnancy (abnormal growth of tissue in your uterus) or a multiple pregnancy. Low levels of hCG in your blood could indicate a miscarriage (spontaneous loss of pregnancy) or ectopic pregnancy (implantation of the egg in a location outside of the uterus).