i found this...a little long but interesting...
As a focus for further discussion related to these queries, let’s start with progesterone. Following ovulation, what’s left of the follicle (the corpus luteum) begins to make the hormone progesterone that helps to prepare (decidualize) the lining of the uterus (the endometrium) to receive the fertilized egg, aiding attachment and implantation of the early embryo. With implantation, the fetal trophoblast cells start producing the hormone hCG that sends a ‘message’ back to the corpus luteum to ‘stay healthy and keep making progesterone.’ Production of progesterone by the corpus luteum is necessary to support the development of the placenta during the first 7-8 weeks of the pregnancy. After that point under normal circumstances, the placenta itself takes over progesterone production at a level sufficient to maintain the pregnancy.
Decreased progesterone production following ovulation or inadequate production of hCG or placental progesterone has been found to accompany pregnancy abnormalities that result in miscarriage. Defective production of these hormones may precede by weeks the identification or loss of an abnormal pregnancy (Hahlin, et al., Hum Reprod 1990;5:622–626) or ectopic (tubal) pregnancy (Yeko, et al., Fertil Steril 1987;48:1048–1050; Ledger, et al., Hum Reprod 1994;9:157–160). Indeed, there is good evidence to suggest that serum progesterone measured in early pregnancy is the most reliable single predictor of pregnancy outcome in natural conceptions (Al-Sebai, et al., Br J Obstet Gynaecol 1995;102:364–369; Daily, et al., Am J Obstet Gynecol 1994;171:380–383) even in the absence of a pregnancy detected by ultrasound (Elson, et al., Utrasound Obstet Gynecol 2003;21:57–61). Ioannides and colleagues (Human Reprod 2005;20:741-6) demonstrated that even in IVF pregnancies supplemented with progesterone, a single serum progesterone on day 14 post-oocyte retrieval and fertilization (4 weeks gestation), could “highly (but not completely) differentiate between normal and abnormal pregnancies.” Women with viable intrauterine pregnancies “had significantly higher serum progesterone levels (median: 430, 95%CI: 390–500 nmol/l) compared to those who had either an abnormal pregnancy (72, 48–96 nmol/l; P<0.001) or failed to conceive (33, 28–37 nmol/l; P<0.001).” It is interesting to point out that as the result of their findings, they hypothesized “that endogenous progesterone is already sufficient in viable pregnancies and that exogenous progesterone administration will not rescue a pregnancy destined to result in a miscarriage.”
Although progesterone is highly effective at differentiating normal from abnormal pregnancies, it is still not routinely used at most institutions for this purpose because of the expense, inexperience of provider interpretation, and the more widespread availability and high reliability of quantitative hCG testing. hCG can usually be detected by routine blood assays within 10-11 days following conception (7-8 days by highly sensitive assays) and in the urine at 12-14 days (just preceding or coincident with the time of expected menstruation). Serial quantitative blood testing of hCG is a useful approach to evaluation of early intrauterine pregnancy viability and ectopic pregnancies. In 80-90% of normal pregnancies, hCG levels will double every 48-72 hours, peak at 8-11 weeks gestation and then fall off to a stable lower level for the rest of the pregnancy.
If hCG levels are low for a calculated gestational age, this can indicate a nonviable or ectopic pregnancy. However, it is generally recommended that decisions regarding viability not be made by a single hCG level alone. It could be low simply because the pregnancy is not quite as far along as expected (e.g., in circumstances when women ovulate later in their cycles than expected or are not “sure” of their last menstrual period) or as the result of normal variation in hCG levels in different women and different pregnancies. More ominous are situations in which the hCG is not rising appropriately over time.
However, at low levels of hCG, the woman is rarely in immediate danger, even if she has an ectopic pregnancy, so the prudent approach in situations in which the pregnancy is desired is to simply wait, repeat the hCG levels periodically, every 2-3 days, and perform an ultrasound to look for evidence of an intrauterine pregnancy when the hCG level is at the point where that becomes possible. Usually a gestational sac can be seen within the uterine cavity between 4 and 5 weeks and when the hCG is in the range of 1000-2000 mIU/mL. By 6 weeks, a ‘fetal pole’ is usually visible and the hCG is > 5000 mIU/mL; and by 7 weeks, fetal cardiac activity is readily detectable and the hCG is > 20,000. I can relate many personal experiences with patients who started out with an unexpectedly low hCG that went on to have normal, healthy pregnancies, so patience is a virtue under these circumstances.
Labels: early miscarriage, hCG, progesterone
