Help! FT3 below reference range despite increased dosage during pregnancy

[iriscandy]

Hi, I was diagnosed with Hashimoto’s thyroiditis in 2015 and has been taking Levothyroxine ever since. I started a gluten-free diet nearly 2 years ago.

Before I found I was pregnant, my dosage was 75mcg/day. And the last blood test before pregnancy was:

TSH 0.93 (0.35-5.5 mIU/L)

FT4 15.4 (10-20 pmol/L)

FT3 3.84 (3.1-6.8 pmol/L)

Ferritin 12(15-250 ug/L)

Vit B12 896 (200-900 ng/L)

Folate 20.1 (2-17 ug/L)

Week 5

I found I was pregnant, my dosage was increased to 100mcg/day

Week 9

I did a blood test weeks at my midwife booking appointment:

TSH 1.1 (0.35-5.5 mIU/L)

FT3 3.5 (3.1-6.8 pmol/L)

I discussed the result with my GP and mentioned that I felt extremely sensitive to cold. I suspected it’s due to my hypothyroidism. She referred me to see an OB and increased my dosage further to 125 mcg, which she said is in line with NICE guideline of 25-50 mcg increase.

Week 14

As I could get a blood test done in my GP surgery before the OB appointment, I took a Medicheck finger-prick blood test instead:

TSH 0.296 (0.27-4.2mIU/L)

FT4 22 (12-22 pmol/L)

FT3 4.11 (3.1-6.8pmol/L)

The OB thought my current dosage of 125 mcg might be too much so I had a blood test done in the hospital again:

TSH 0.15 (0.27-4.2 mIU/L)

FT4 19.6 (12-22pmol/L)

FT3 3.7 (3.5-6.5 pmol/L)

I was told to lower the dosage back to 100 mcg after the OB reviewed my results.

Week 19

I did a blood test again in my GP surgery:

TSH 0.66 (0.27-4.2 mIU/L)

FT4 12.5 (12-22pmol/L)

FT3 3.2 (3.5-6.5 pmol/L)

Ferritin 52 (15-250ug/L)

This time my FT4 was significantly lower than Week 14's result and my FT3 was even lower than the reference range.

I’m really worried as I read low thyroid hormones will harm baby’s development and may increase the risk of miscarriage or premature birth. But if I increase my dosage again to 125 mcg, it might bring my TSH down to be hyper, which I was told is not good to the baby either. What should I do?

Any advice would be much appreciated. Thank you.

[greygoose]

I really don't know much about thyroid hormones during pregnancy. But, I just wanted to reassure you that having a low TSH is not what makes you hyper. In fact, you cannot become hyper if you are hypo, the thyroid doesn't jump around like that. And, the TSH is of no importance to your pregnancy - or much else, come to that - although the low TSH could be one of the reasons for your conversion problem, but there's not much you can do about that.

You could be over-medicated, but your FT3 is very low. So, although your FT4 is high, you are not over-medicated, you are just not converting that all that T4 to T3. But, if it's any consolation, it's the T4, I believe, that crosses the placenta/blood barrier, not the T3.

Reasons for poor conversion are many and varied, but I imagine that that low ferritin is not helping. Don't they give you iron tablets when you're pregnant any more? When I was pregnant, 50 years ago, that was the first thing they did, hand out the iron tablets. I think you should ask about your low ferritin, because it's not good for it to be that low.

However, whatever the reason for poor conversion, there is not a quick fix. What you need is not to increase your levo, but to have a little T3 added to your levo. I suggest you ask your doctors about that, because your FT3 should not be below range, like that. But, how do you feel? That's the most important criteria.

[iriscandy in reply to greygoose]

Thanks a lot for your reply.

I've been taken iron tablets soon after the blood test showed I've got low ferritin. But the Ferrous fumarate tablets 210mg I got from GP made my morning sickness and constipation worse, so I take Ferrochel tablets 36mg instead. I guess it's because the one I take is low strength and the baby needs iron at the same time, my ferritin level hasn't been improved a lot. I'll double the dosage from now on.

My conversion has always been poor since I was diagnosed. But all the GPs and endocrinologists I've seen think my FT3 values are fine and refuse to give me T3 or a combination of T3/T4. I've heard from other patients that it is now extremely difficult to get a T3 prescription from NHS. I'm worried that this time I couldn't pursuade them either. If not, does that mean my only choice is to go private?

[greygoose in reply to iriscandy]

I'm not sure that going private would help. Private doctors are still NHS trained, they don't have any extra knowledge. Many people have paid out a lot of money only to be sorely disappointed in the end. It's seems it's often best just to buy your own, but you could ask your doctor if he will monitor you whilst you take your own T3. They really are all very ignorant.

[diogenes Remembering]

For pregnant women in the 2nd and 3rd trimesters of pregnancy (that is, week 14 and onward, the healthy FT4 and FT3 range are somewhat reduced compared with non pregnant women. For FT4 this is about 75% of normal which relates to low normal in that range. For FT3, the average value is less than 50% up the normal range. So, say if the FT4 range was 12-22, then a target FT4 would be about 14 or less. At the same time FT3 average would for a range 3.5-6.5 would be about 4.5-5. If you are on T4 then the FT4 might have to be higher than that because of conversion problems to T3. So the aim should be to get FT3 around 5 and forget the FT4/TSH values. Getting FT3 right is the ultimate aim. Your last results show undermedication.

[iriscandy in reply to diogenes]

Thanks a lot for your reply. You are right, getting FT3 right is the ultimate aim, but unfortunately my GP and OB only care about TSH. Could you please let me know where I can find papers or articles related to the 2nd and 3rd trimester FT3/FT4 reference range you mentioned in your reply? I want to do some homework before talking to my GP/OB again. Thank you.

[diogenes Remembering in reply to iriscandy]

Try this one:

Gestational age-specific reference ranges from

different laboratories misclassify pregnant

women’s thyroid status: comparison of two

longitudinal prospective cohort studies

Sofie Bliddal, Ulla Feldt-Rasmussen, Malene Boas1,*, Jens Faber2, Anders Juul3,

Torben Larsen4 and Dorthe Hansen Precht5

Department of Endocrinology, Section 2132, Copenhagen University Hospital, Rigshospitalet, Blegdamsvej 9,

2100 Copenhagen, Denmark, 1Department of Pediatrics, Copenhagen University Hospital, Hillerød, Denmark,

2Department of Endocrinology, Copenhagen University Hospital, Herlev, Denmark, 3Department of Growth and

Reproduction, Faculty of Health and Medical Sciences, Copenhagen University Hospital, Rigshospitalet, University

of Copenhagen, Copenhagen, Denmark, 4Department of Fetal Medicine, Copenhagen University Hospital,

Holbaek, Denmark and 5Department of Child Psychiatry, Copenhagen University Hospital, Roskilde, Denmark

*(M Boas is now at Department of Growth and Reproduction, Faculty of Health and Medical Sciences, Copenhagen

University Hospital, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark)

Abstract

Objectives: Correct interpretation of thyroid status during pregnancy is vital to secure fetal development. Pregnancy-related

changes in maternal thyroid status necessitate the use of gestational age-specific reference ranges. In this study,

we investigated between-laboratory reproducibility of thyroid reference ranges in pregnant women.

Design: Comparison of two longitudinal prospective cohort studies including 255 (cohort 1) and 101 (cohort 2) healthy

antibody-negative Danish pregnant women attending prenatal care at Copenhagen University Hospital.

Methods: Different immunoassays were used to measure thyroid hormone levels in the two cohorts. Thyroid hormone

reference ranges were established for every 5 weeks of gestation. Differences between cohorts were explored through

mixed-model repeated measures regression analyses. By applying reference ranges from one cohort to the other,

the proportion of women who would be misclassified by doing so was investigated.

Results: TSH increased and free thyroxine (FT4) decreased as pregnancy progressed. Results indicated highly significant

differences between cohorts in free triiodothyronine (FZ21.3, P!0.001) and FT4 (FZ941, P!0.001). TSH levels were

comparable (PZ0.09). Up to 90.3% of the women had FT4 levels outside their laboratory’s nonpregnant reference range,

and up to 100% outside the other cohort’s gestational-age-specific reference ranges. Z-score-based reference ranges

markedly improved comparison between cohorts.

Conclusion: Even in the same region, the use of gestational-age-specific reference ranges from different laboratories

led to misclassification. Up to 100% of maternal FT4 levels fell outside the other cohort’s reference range despite similar

TSH levels. In clinical practice, thyroid testing of pregnant women without adding method specificity to gestational

age-dependent reference ranges will compromise patient safety.

European Journal of

Endocrinology

(2014) 170, 329–339

European Journal of Endocrinology

Thyroid status misclassification

in pregnancy

170:2 329–339

eje-online.org 2014 European Society of Endocrinology

DOI: 10.1530/EJE-13-0672

Put in th DOI number and the article is downloadable.

[diogenes Remembering in reply to iriscandy]

There is also this Guideline from a Scottish Health Area:

Guidelines for Thyroid Function Testing in Primary Care - Thyroid UK