Effect of Thyroid on Pregnancy
Follow up of a case of miscarriage at 11 weeks.
Q: I truly appreciate your prompt response to my query. I forgot to mention that I am under treatment for thyroid, however we planned pregnancy only after it was completely under control. During pregnancy, TSH test was well under normal range. However after the treatment started, my periods, which were otherwise always timely, got delayed by 5 days for the first 2 months. Next month it was on time but heavy and only for 2 days. I conceived post this menstrual cycle. Does such a change in menstrual cycle impact quality of egg?
It’s unlikely that the pattern of your menses or the quality of your egg caused the abortion. Much more chances are that it was the development of the fetus after conception that might have been affected.
Thyroid dysfunction of any type (hyperthyroidism or hypothyroidism) can be a cause of miscarriage. Since you had some thyroid dysfunction in the past, even though you were adequately treated, this may be the reason for your abortion.
This is because pregnancy influences the functioning of the thyroid tissues. Even in normal pregnancies, a mild hyperthyroidism usually occurs during the first trimester. It disappears itself in later trimesters.
Pregnancy can be a cause in itself for recurrence of Grave’s disease (hyperthyroidism) or Hashimoto’s disease (hypothyroidism) in women prone to thyroid disorders.
Guidelines for Thyroid Hormone Levels
It is recommended that TSH should be kept below 2.5 mIU/L prior to conception. This lowers the risk of the TSH elevating in the first trimester.
During the first trimester, the TSH level should be maintained at a level between 0.1 and 2.5 mIU/L, 0.2 to 3.0 mIU/L during the second trimester, and 0.3 to 3.0 mIU/L in the third trimester.
If positive for thyroid antibodies, even with normal TSH levels in the early stages of pregnancy, there is a risk of becoming hypothyroid later during term.
How pregnancy affects thyroid functions needs to be clearly understood. Read here for understanding how to manage thyroid dysfunctions during pregnancy.