I’ve been promoting iodine in pregnancy for a couple years now.
And didn’t even guess low thyroid levels could be related to posterior fetal position! I just had a hunch we were seeing more slow starts to labor, to the frustration of the mothers and to a point that didn’t seem like a simply gentle start. Also, for women who had a tough time getting pregnant due to hormone issues.

So this new study by researchers from the University of Tilburg is a Christmas present to Spinning Babies :
12-23-09 BBC news (https://news.bbc.co.uk/2/hi/health/8425901.stm)

“Low hormone levels in pregnancy linked to hard birth

Too little of the hormone thyroxine is already known to complicate pregnancy, increasing the risk of miscarriage, premature birth and pre-eclampsia.

Now a Dutch team has found even “low to normal” levels of thyroxine may cause problems, Clinical Endocrinology says.

Babies were more often positioned wrongly, making labour more difficult.

Although still head down, the babies tended to face the wrong way – towards their mother’s back rather than stomach.

Not only are these labours generally longer and harder, they are also more likely to end in an assisted delivery with forceps, ventouse or a Caesarean.”

It does highlight the importance of checking thyroid hormone levels in pregnancy Hormone expert Professor John Lazarus