Bechorot 22: Miscarriage and Ritual Impurity

Today the rabbis discuss miscarriage in general, which is disturbing to an adult woman who has had a miscarriage.  The rabbis assert that a fetus dies in its mother's, it only imparts ritual impurity from when the womb opes and the head of the fetus is round like the 'skein of yarn' (Massechet Oholot 7:4).

Tum'ah belu'ah, swallowed defilement, does not ritually defile (Massechet Hullin 7) If it is contained within the mother's womb.  Once the uterus has opened and we can see the head of the fetus, round like a skien of yarn (whatever that may be) the ritual impurity affects the entire home.

So a woman who has just lost her pregnancy also loses the right to define whether or not her fetus was large enough to be considered defiled/defiling.  She has to face the transformation that ritual defilement will brig upon her household and she will mourn without ritual or acknowledgement.