Thyroid Issues During and After Pregnancy: A Patient's Journey - Breast and Thyroid

Thyroid issues

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Hello Dr.
Wu,
After giving birth to my first son naturally on January 31 last year, I became pregnant with my second child about four months later.
Starting two to three months postpartum, I experienced insomnia, heat intolerance, and severe hair loss.
At that time, I thought it was just insomnia and not properly resting during the postpartum period, and I often had headaches, back pain, and felt unwell, so I didn't pay much attention to it.
Later, around the end of May this year, my menstrual period was two days late, and I took a pregnancy test which confirmed that I was pregnant.
However, a few days prior, I had a cold, and as I was recovering, I noticed my neck starting to swell.

I then visited your hospital, where Dr.
Dong from the internal medicine department examined me and diagnosed me with hypothyroidism.
He mentioned that I might have had this condition for a long time and that it could be hereditary in my family.
He prescribed Eltroxin (T4) 0.1 mg for me.
During the early stages of my pregnancy, I continued taking the medication, but I still experienced insomnia.
I had a bout of vaginal bleeding and was prescribed medication to support the pregnancy.
I continued taking the thyroid medication until about a month and a half into my pregnancy, when I became extremely drowsy; I would fall asleep while watching TV or sitting anywhere, and I felt persistently tired.

As I approached five months of pregnancy, the swelling in my neck subsided, and I no longer felt drowsy, so I stopped taking the medication.
After about two to three months of self-discontinuation, I researched online and found that stopping the medication could be harmful to the fetus (such as causing cretinism), so I went for a blood test.
Dr.
Dong confirmed that I still had hypothyroidism (on January 12 this year, when I was nearly eight months pregnant, my FREE T4 was 1.43 ng/dl, T3 was 216.0 ng/dl, TSH was 1.061 uIU/ml, and Ab-TSH Receptor was 13.1 U/L).
The doctor noted that it was quite remarkable that I had not miscarried and was able to carry the pregnancy to eight months.

On February 12 this year (when I was about 37 weeks and two days pregnant), I gave birth naturally to my second son.
His thyroid was normal upon examination.
However, problems arose postpartum.
I continued taking the Eltroxin prescribed by my doctor (and I have also been taking a prenatal vitamin containing 150 mcg of iodine since the beginning of my pregnancy), but as I was nearing the end of my postpartum recovery, I began experiencing insomnia again and had an unexplained fever that resolved on its own after one night (my neck swelled slightly again but subsided a few days later).

Around 40 days postpartum, I experienced abnormal bleeding, which was treated with medication.
By the end of March, I started having irregular heartbeats (sometimes normal, sometimes rapid), and my limbs felt weak and trembled uncontrollably.
Initially, I thought I was just hungry, but later realized that even after eating, the symptoms persisted.
I felt fatigued regardless of whether I was sitting, standing, or lying down, but resting in bed alleviated the discomfort.
Recently, I noticed that my right neck was slightly more swollen than my left, so on April 17, I returned for a follow-up and mentioned this to my doctor.
My blood pressure was normal, but my heart rate was elevated at 144 beats per minute.
The doctor suggested that I might be experiencing a relapse and arranged for blood tests and an ultrasound on April 19.

Regarding my heart discomfort, Dr.
Dong prescribed the usual Eltroxin (T4) 0.1 mg, along with Inderal 10 mg and Thiamazole 5 mg tablets.
Since I am breastfeeding, I asked the doctor if these medications were safe, and he assured me that it was fine to take Inderal and Thiamazole three times a day, along with Eltroxin once a day.
However, when I researched these medications online, I found that Inderal should be avoided during breastfeeding unless necessary, and Thiamazole should not be taken while breastfeeding.
I also read that Thiamazole is used for hyperthyroidism (though I am unsure if I misinterpreted this).

I am very concerned and would like to ask Dr.
Wu a few questions:
1.
Given my situation, if I want to continue breastfeeding, can I safely take the Inderal and Thiamazole prescribed by my doctor? Will these medications pass into my breast milk? If they do, what adverse effects could they have on my child?
2.
Since the doctor initially prescribed Inderal for my heart issues and later added Thiamazole, does this suggest that he suspects I may have developed hyperthyroidism?
3.
If I had hypothyroidism during pregnancy, is it possible for me to develop hyperthyroidism postpartum?
4.
Considering my situation, if I had hypothyroidism during pregnancy, could my thyroid function return to normal postpartum? Is it possible that I have become normal again, and that continuing to take thyroid hormone could be causing symptoms similar to hyperthyroidism? Before pregnancy, I did not experience irregular heartbeats or tremors while on medication, which makes me question my condition.

5.
If I do develop hyperthyroidism and require medication treatment, can I still breastfeed? I am worried because I read online that it is not safe.

I appreciate Dr.
Wu taking the time to answer my questions amidst your busy schedule.
Wishing you peace and health.
Thank you.

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Jia Qian, 20~29 year old female. Ask Date: 2006/04/18