I received the following letter from a reader who went through a similar experience:
I am not a doctor, but I have Gitelman's, and 16 years ago, was pregnant and ended up having to go on amiloride at the start of my second trimester, because my potassium and magnesium levels just tanked. Being part of proving the track record on the viability of amiloride in pregnancy was a scary time, I tell you what. Your patient's experiences are similar to mine, though I did not require the magnesium IVs she apparently does during gestation.
The great news is my son turned out healthy, and without any sign of potassium disorders of any sort, so far as we can tell at nearly 16. He's healthy, bright, nearly 6 ft - no indication at this time that he was harmed in any way by the fetal exposure to amiloride.
And another point to pass along - after he was born, I had my breast milk checked for traces of amiloride, and it passed whatever screens were applied. Therefore I nursed him for about 9 months, though I supplemented with formula. It was an acceptable risk for me - since I know the literature does not record any data on nursing while on amiloride, I thought I'd pass along one uncontrolled anecdote for you to ponder. [Note: on further communication the patient clarified that she did not take amiloride during breast feeding]
Anyway, please pass this information along to your patient - I am sure it will help her peace of mind to know another successful long term outcome. It was a scary time for me, and without the widespread use of Internet back in 1995, the only piece of mind I got was by tracking down Dr. Almeida, who wrote the 1989 paper about Gitelman's in pregnancy. I spoke to one of his nurses to see if they could give me some info on long term followup on the baby, but the mother had disappeared after giving birth, and they had nothing to report.
Best of luck to your patient - I know what she's going through.
Final note for your patient going forward: Getting my levels back up after the birth was a bit of a challenge, I recall. But many of the details have been lost to time and the fog of war, I'm afraid - I will just say that the first month post-partum was pretty rough on me.