Prior iodine exposure and impact on thyroid function during controlled ovarian hyperstimulation: A prospective study

[helvella]

The eternal thyroid question - iodine. This time with the positive of being a prospective study and with a closely defined context.

Aust N Z J Obstet Gynaecol. 2021 Aug 18.

doi: 10.1111/ajo.13419. Online ahead of print.

Prior iodine exposure and impact on thyroid function during controlled ovarian hyperstimulation: A prospective study

Rachel A Bradbury 1 2 3 , Darshika Christie-David 3 4 , Howard C Smith 1 2 , Karen Byth 5 6 , Creswell J Eastman 2 3

Affiliations

• PMID: 34406645

• DOI: 10.1111/ajo.13419

Abstract

Aims: Iodine supplements are recommended for women planning pregnancy, but their impact on thyroid function during controlled ovarian hyperstimulation (COH) and into pregnancy is unknown. The aim of this study was to assess the impact of iodine supplementation on thyroid function during COH.

Methods: One-hundred and six euthyroid women (thyroid stimulating hormone (TSH) 0.4-2.5 mIU/L) planning their first COH cycle were subdivided according to iodine supplementation (nil, <6 months, ≥6 months) and compared to levothyroxine (LT4)-treated controls. Serial TSH, free thyroxine, free triiodothyronine and thyroglobulin (Tg) levels were recorded at four time points: (i) baseline, (ii) day 7 ovarian stimulation, (iii) ovulation trigger and (iv) two weeks post oocyte retrieval. Oocyte numbers, fertilisation rates and pregnancy outcome were recorded.

Results: TSH increased during COH for those women taking iodine supplements for ≥6 months (P = 0.025). One quarter recorded a TSH level >2.5 mIU/L before embryo transfer. A similar increase in TSH was demonstrated by LT4-dependent controls (P = 0.024) but not the remaining subgroups. Tg levels did not change during COH in any group but decreased significantly post oocyte retrieval if nil iodine (P < 0.0001) or supplemented for ≥6 months (P < 0.005). Iodine supplementation did not influence oocyte count, fertilisation or implantation rates. Women taking iodine for <6 months were four times more likely to achieve a live birth than women taking iodine for longer.

Conclusions: Women taking iodine supplements for ≥6 months are less able to adapt to the thyroidal demands of COH, with responses comparable to LT4-dependent patients.

Keywords: iodine; ovarian induction; pregnancy; thyroid hormone.

Full paper is behind a paywall.

pubmed.ncbi.nlm.nih.gov/344...

[humanbean]

Iodine supplements are recommended for women planning pregnancy

That is news to me!

Tg levels did not change during COH in any group but decreased significantly post oocyte retrieval if nil iodine (P < 0.0001) or supplemented for ≥6 months (P < 0.005)

That result seems to be contradictory, but is nevertheless interesting. I wonder how that situation could have arisen (from a biochemical point of view).

It's a pity their abstract doesn't mention any impact on Free T4 and Free T3. If the researchers are honest in their abstract then presumably there was no impact and only TSH changed significantly for some subjects, but not the actual thyroid hormones.

But if my assumption is accurate then changes in TSH with no significant differences in Free T4 and Free T3 could actually be helpful. Or am I just wittering?

[helvella Administrator Thyroid UK in reply to humanbean]

As so often, it depends where you are and what you read.

Iodine

Iodine is a mineral needed to make thyroid hormones.

These hormones:

control your body's metabolism

help your baby’s bones and brain develop

If you eat foods including pasteurised milk, pasteurised dairy products and fish you'll probably get enough iodine.

If you don’t eat these foods, you’re more likely to be short of iodine so talk to you midwife or GP for advice about supplements.

nhsinform.scot/ready-steady...

ukiodine

Iodine in pregnancy and lactation (breastfeeding)

Why is iodine needed?

Iodine is important for the development of the baby’s brain. For this reason it is important that pregnant women meet their requirement for iodine so that sufficient iodine and thyroid hormones are transferred to the developing baby throughout pregnancy.

As the brain continues to develop in early life, iodine is important during breastfeeding. Breast milk is the only source of iodine for babies who are exclusively breastfed.

Iodine before conception

You should make sure that you have been having enough iodine in your diet for several months before you get pregnant. This is because iodine is required from the very early stages of pregnancy – before you may even know that you are pregnant.

Your body can store iodine in the thyroid gland. These stores of iodine can then be used to provide thyroid hormone and iodine to your developing baby and to make sure that you are able to continue to produce sufficient thyroid hormones throughout your pregnancy.

It is therefore very important that if you are of childbearing age, and if you are planning a pregnancy, you make sure that you are consuming enough iodine.

How much iodine do you need?

The recommendation for adults is for 150 micrograms of iodine per day. If you are of childbearing age it is important to meet this requirement so that you can prepare for pregnancy.

During pregnancy and breastfeeding, the recommendation is for 200 micrograms/day [according to the European Food Safety Authority (EFSA) 2014].

Which foods are important for adequate iodine?

See our section on diet. The main sources of iodine in the UK diet are milk and dairy products. Fish is also a rich source of iodine.

The diet advice that is already given to women who are pregnant will ensure good sources of iodine are eaten. For example, the NHS advise that if you are pregnant you should have at least two portions of fish per week (one of which should be an oily fish). This will provide iodine – for example, a 120g portion of cod will give approximately 190 micrograms of iodine. The iodine from fish can be stored in the thyroid to be used on days of the week when you don’t eat fish.

You need to take care with certain types of fish when you are pregnant or planning a pregnancy – see NHS pages for full details. You should not have more than two portions of oily fish (e.g. salmon, mackerel and trout) per week, no more than two tuna steaks or four medium-sized cans of tuna per week. In addition, you should avoid shark, marlin and swordfish. Shellfish should be well cooked and should not be eaten raw.

What about iodine supplements during pregnancy?

Do not take kelp or seaweed supplements as they can provide excess iodine.

It can be difficult to meet the higher demands of pregnancy through diet alone if you do not regularly eat foods that are good sources of iodine. Therefore you might need to take a supplement containing iodine. Ideally this should commence around 3 months before you become pregnant – much like folic acid supplements.

Some supplements for pregnant women (e.g. multivitamin and mineral supplements) contain iodine. The dose of iodine in these supplements should be approximately 140 or 150 mcg/day. This means that the remainder of the iodine requirement can be met from the diet. You should not take supplements containing higher doses than this as, along with the iodine from the diet, you could have too much iodine.

Make sure that if you are pregnant, the supplement that you choose is suitable for pregnancy. For more information see NHS advice.

If you have thyroid disease, are taking other medication, or have experienced iodine deficiency over many years, you should speak to your GP before taking additional iodine.

Text written by Dr Sarah Bath and Professor John Lazarus (August 2015, updated January 2020)

ukiodine.org/iodine-in-preg...

[tattybogle in reply to humanbean]

i linked someone to a study a few months ago about COH / thyroid, and i vaguely remember it did have T4 ( & possibly T3) data. as well as TSH .

Unfortunately i have no idea who i relied to with it.

If i find it i'll add it here later. ( i may be some time lol )