Pregnancy sickness and parent-offspring conflict over thyroid function.
Forbes S.
Author information
Department of Biology, University of Winnipeg, 515 Portage Avenue, Winnipeg MB R3B 2E9.
Abstract
Pregnancy sickness is widespread in human mothers but its etiology, somewhat surprisingly, remains unclear. Human chorionic gonadotropin (hCG) has long been considered a prime hormonal suspect, but the correlation between pregnancy sickness and hCG levels is imperfect resulting in uncertainty about its causal role. As others have noted part of this uncertainty likely stems from the structural and functional diversity of hCG. One enigmatic role of hCG is its action as a thyroid stimulator during early gestation. Native hCG is weakly thyrotropic but is produced in prodigious quantities and suppresses the production of thyroid stimulating hormone (TSH) but not curiously when TSH levels are in the higher deciles. Higher levels of hCG induce higher maternal production of thyroxine (T4). hCG thus appears to augment and sometimes even supplant TSH in the regulation of thyroid hormone in early gestation. This has lead to the suggestion that hCG serves as a backup system, albeit incomplete, for the production of essential thyroid hormone during pregnancy. Another interpretation, however, is that hCG, produced by the embryo, serves as a second control circuit for the thyroid during pregnancy. If so, it serves embryonic interests that are at odds with maternal interests (maternal-embryo conflict) under conditions of iodine deficiency. Iodine is an essential micronutrient for neurodevelopment and thyroid function, and has been in short supply for most humans over most of our evolutionary history. Iodine deficiency during gestation has severe impacts on embryo neuromotor development, but also induces thyroid disease in mothers, impairing her future reproductive prospects. Under this view, embryos use hCG to push mothers to release more thyroid hormone. hCG, however, is produced outside the normal maternal thyroid control circuit and thus is not subject to a normal negative feedback. hCG also serves multiple functions simultaneously therefore its production is likely not fine-tuned for thyroid function per se. hCG levels may remain high even when thyroid hormone production is more than sufficient to meet the needs of mother and embryo. Instead, the system appears to be regulated at the back end by clearing surplus hormone using placental Type II (D2) and Type III (D3) deiodinases. As maternal thyroid hormone levels rise, placental D3 is upregulated, shunting more T4 and T3 into a deactivating pathway. The metabolites that result, particularly the inert metabolite of T4, reverse T3, are correlates of surplus thyroid hormone production and thus are strong candidates for the proximate triggers of pregnancy sickness. Nausea and vomiting of early pregnancy thus arises as a by-product of an antagonistic pleiotropy between mother and embryo over the allocation of iodine: when dietary iodine is scarce, a benefit accrues to the embryo at a cost to mother; when iodine is plentiful, pregnancy sickness ranging from frequently mild to occasionally severe, is a sequelae of undiminished embryonic demands. If pregnancy sickness serves as a marker of thyroid function, an absence of first trimester nausea and vomiting sickness may indicate a higher priority for testing of thyroid function to avert the inimical effects of hypothyroidism during gestation.
Interesting , I had to have acupuncture to alleviate morning sickness with my second baby, it was so bad - I was on Thyroxine though and my thyroid was controlled.
Interesting! I was pregnant three times pre hypo being confirmed and each pregnancy the sickness was worse than before which my GP thought was age related. I was also told not to worry as it was a good sign-very hard to take that on board when your head in over a bucket most of the time for months! My husband agreed ( a science based Endo) and I was told why but I can't remember now! I was also sick throughout labour with my third. The previous two I vomited just after delivery. The midwife wasn't concerned other than it difficult to push at one end and vomit at the other at the same time! By the time I saw ward sister I was fine but she had this concerning report on me and she couldn't take in how good I was by then. So whatever the cause the body reacts quickly to the changes-better than it does now!
Omg they tell you so much nonsense about unpleasant things. I do hope when the doc is vomiting blood after a dodgy takeaway someone strokes their brow and gently says 'It's a great sign you're heaving up your guts because it will really help you get over this bout of food poisoning.'
I appreciate that some unpleasant things are a 'good sign' but I think there's a more compassionate way to say it. And recently we all saw what can happen if you have a really savage bout of hyperemisis. That isn't much good for you or your baby.
Your experience reminds me of the story my mum tells of being in labour with me and the obstetrician chatting with my dad telling him how various indigenous peoples used to hunt and gather, step behind a bush, push the baby out, sling it on their back and return to their work. It might be true (??) but there's a time and a place. My mum obviously remembers how it made her feel to hear it because I'm 46 and she still tells the story.
Oh Silver Fox!! I bet it wasn't funny at the time,but picturing your "Two ended Delivery"
gave me " Monday Morning Giggles ". I bet your stomach muscles were working overtime, Oh the joy of bringing our babies into the world,not to mention what it does to your hormones.I know someone who on her first visit to her Endo was asked questions going right back to child birth.....I can almost feel another survey coming on.
In addition to other hypo symptoms, I am suffering from what I can only describe as morning sickness, going on over a year now (well this is how felt when pregnant, and no I'm not, I'm well past menopause )
so what does this say about me ? Could this be why ?
"Under this view, embryos use hCG to push mothers to release more thyroid hormone."
I will have to read this through a few more times to fully understand.
Thanks Rod. I know now that I know nothing. The more I read the more confused I become.
I sailed through my first pregnancy, I had "flu" about a year later,then another year on and pregnant with my second I had morning sickness. I put all my illness symptoms down to working full time and raising a family,under difficult circumstances . Was this the beginning of autoimmune illness?? I've never been the same since,slowly going downhill. Now I'm crawling through treacle.
Hi Flatfeet,I think now I have tweaked the T3 I am feeling better in some respects,usual thyroid ones. I'm still having problems with energy levels and digestion. I think my problems are autoimmune and need to get the different consultants to recognise that these things come together not in pigeon holes. x
No 'morning' sickness with my two sons, but after having sub-total thyroidectomy at 14 weeks while expecting my daughter the nausea was nonstop, although no actual vomiting. Also went completely off tea and could only stand warm lemon barley water. As soon as my daughter was born went straight back to tea. Was also told it was a good sign that all was well. Janet.
I didn't want to be left out of this due to being merely a man, so I offer you two products from the food awards at which I'm currently stewarding, in the hope they will alleviate any memories of queasiness brought on by reading all the above: Pickled Sprouts, anyone ? How about Marmite flavoured fudge then?
Always found it surprising that whilst I like Marmite very much on bread or toast (or croissants), almost everything that uses it as an ingredient is foul.
Sprouts are, quite simply, foul - regardless.
Rod
I've had a bash at trying to convert that abstract into plain English. Honestly, "inimical"?? Grrr. Let me know if you don't agree with my interpretation...
No one really understands why some women get morning sickness. Some people think human chorionic gonadotropin (hCG) is the cause but the relationship between pregnancy sickness and hCG levels isn't a straightforward one. That's because hCG seems to have more than one function.
HCG stimulates the thyroid to produce more thyroxine during early pregnancy, especially when the thyroid seems unable to respond to rising TSH levels. Iodine deficiency can cause thyroid disease. It seems that if a pregnant woman is suffering from iodine deficiency the production of hCG acts as a back up system in order to protect the growing baby. Iodine deficiency during early pregnancy can stop the baby from developing properly.
HCG is produced outside the normal thyroid control system--it seems to be driven by the baby's needs rather than the mother's needs. So hCG levels may stay high even when thyroid hormone production has risen enough to meet the needs of the baby. Excess thyroid hormones are cleared out via the placenta. As the mother's thyroid hormone levels rise the placenta gets rid of excess T4 and T3 by turning it into reverse T3. High levels of reverse T3 are often seen where the mother suffers morning sickness.
Nausea and vomiting during early pregnancy can therefore be linked to the mother suffering from iodine deficiency. The occurrence of morning sickness could be used to assess thyroid function. The absence of morning sickness may indicate thyroid disease in the mother.
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xx
The NHS is a sick joke!
Euthyroid sick syndrome
Unknown ongoing sickness 
Sick of going around in circles 
Sickness appeal help.
