The Kollel wrote-
>>(a) A Ketanah, a pregnant woman and a feeding mother are permitted to use a cloth to avoid becoming pregnant, according to Rebbi Meir (in the opinion of Tosfos DH 'Shalosh, they are even obligated to do so). This is because ...
1. ... a Ketanah - might become pregnant, in which case she is in danger of dying.
2. ... a pregnant woman - might become pregnant again, and the second
fetus will squash the first one and kill it.
3. ... a feeding mother - might become pregnant, and will wean her baby prematurely due to her pregnancy.<<
These seem strange. Is it really possible to get pregnant again? Or to not have sufficient time to wean?! Seems impossible!
Rav Shmuel Horowitz showed me a news report of a case in which a woman did become pregnant again. As for time to wean, this seems to be an even more likely and common possibility (of course, with today's nutritional supplements and substitutes for milk, premature weaning would not pose a danger to the baby's life, but in former days, such a situation would indeed pose a danger).