Link Between Progesterone and TSH?

Posted by Kim on May 21, 1999 at 13:52:07
I had a pregnancy loss two months ago, first pregnancy.  Dates said fetus was 16+ weeks but measured only 13 weeks.  Chromosome study came back normal.  I have hypothyroidism.  My early May level was 6.59 (had been 3.2 one month earlier, lab says normal is .2 to 4.75).  Synthroid increased from .075 to .1 yesterday.
I am now pregnant again (approx. 6 weeks).  Dr. ordered progesterone/estrogen test on Monday of this week.  Told yesterday that progesterone was 9.07 ng/dL.  Have been told it takes 10 to sustain pregnancy (have read 15 is expected).  Dr. ordered 200 mg thru week 12 prometrium (I know you've said this is unproven).
Doctor seems to think progesterone problem is responsible for first loss.  This does not seem right though because placenta should have taken over progesterone by the time of the loss (13 weeks).  Additionally, both times now I have gotten pregnant on 1st or 2nd try and my periods are very regular.  The first miscarriage was missed.  I had no blood or cramping and loss was discovered at regular appointment.  Does this sound plausible to you?
Is it possible there is a connection between the TSH problem and progesterone problem? I understand that thyroxine is important in all metabolic activity throughout the body.
I will have sonogram 5/28 but am wondering whether this pregnancy is doomed.  What do you think?  
Posted by hfhs.md.rcs on May 22, 1999 at 12:42:54
Dear Kim:
Thank you for reading prior comments.
Progesterone is not secreted in a continuous fashion: there is a pulsatile release. Ususally the level is sustained above 15 ng/ml in early pregnancy, but one can seen transient drops in association with a healthy pregnancy. Thus, a single low value must be interpreted with some caution. Further, there seem to be patients who do not require the same, high level of progesterone to sustain pregnancy.
Thyroid is an important metabolic stimulant. Hypothyroid patients (by your elevation in TSH, you had become chemically hypothyroid), are more prone to infertility (they do not ovulate)and miscarriage (luteal phase defect is a presume mechanism. Thus, given the combination of high TSH and low Progesterone, I would interpret this to mean the corpus luteum is not doing its job. There is not test that distinguishes a poorly formed corpus luteum (pregnancy is fine and the ovary is not doing the job), a poorly stimulated corpus luteum (pregnancy is failing), or both ovary and pregnancy are OK and the low thyroid issue explains the abnormal measurement.
An hCG level that is doubling normally would imply that the trophoblast (early placenta) and the signal stimulating the corpus luteum is OK. This does not tell us anything about fetal development.
Progesterone in this setting has a logic: the metabolism and/or the corpus luteum formation are the problem and the pregnancy is fine. Supporting the environment until the placenta can take over progesterone production (done by 10 weeks from last menstrual flow) will prevent loss due to poor nutrition by the endometrium. This is in contrast to most "threatened miscarriage" where the ause is unknown and the low progesterone level is usually an indication that the hCG signal is abnormal. Hence the progesterone is a marker of pregnancy failure rather than a cause.
At 13 weeks of pregnancy, the placenta and not the ovary is the source of progesterone.
In the future, the TSH level can be monitored to assure it is not rising. If it is, the patient needs high levels of thyroid hormone supplementation in pregnancy than when non-pregnant.
Keywords: hypothyroidism; progesterone; pregnancy; miscarriage.
This information is provided for medical education purposes and is not a medical consultation. If you have specific questions, please speak with your healthcare provider.