Mishnah Niddah 3:4: If she miscarries a sandal [i.e. a piece of flesh without a face, similar in shape to a sandal] or a placenta, she should sit for [the number of days of impurity and purity required for one who gives birth to] a male and for [one who gives birth to] a female. If a placenta is in a house, the house is impure [as from the impruty of a corpse]; not because a placenta is a fetus, but because there can be no placenta without a fetus. Rabbi Shimon says: the fetus [that was in the placenta] dissolved [into the blood and was nullified] before it came out [and therefore the house is not impure].

הַמַּפֶּלֶת סַנְדָּל אוֹ שִׁלְיָא, תֵּשֵׁב לְזָכָר וְלִנְקֵבָה. שִׁלְיָא בַּבַּיִת, הַבַּיִת טָמֵא. לֹא שֶׁהַשִּׁלְיָא וָלָד, אֶלָּא שֶׁאֵין שִׁלְיָא בְלֹא וָלָד. רַבִּי שִׁמְעוֹן אוֹמֵר, נִמּוֹק הַוָּלָד עַד שֶׁלֹּא יָצָא:

Mishnah Niddah 3:5: If she miscarries a tumtum [person (or animal) with recessed sexual organs whose gender is therefore impossible to determine, presently, by external examination. It is halachically uncertain whether such is male or female] [fetus], or an androginos [person (or animal) with both male and female sexual organs. It is halachically uncertain whether such is male, female or, perhaps, has a uniquely defined halachic gender] [fetus], she should sit for [the number of days of impurity and purity required for one who gives birth to] a male and for [one who gives birth to] a female. If [she miscarries] a tumtum [fetus] and a male [fetus, at once], or an androginosand a male, she should sit for [the required number of days for one who gives birth to] a male and for [one who gives birth to] a female. If [she miscarries] a tumtum [fetus] and a female [fetus, at once], or an androginosand a female, she should sit only for [the required number of days for one who gives birth to] a female. If it emerged in pieces or backwards, once the majority of it has emerged it is regarded as having been born. If it came out normally, [it is not considered born] until the majority of its head has emerged. And what is [considered to be] the majority of its head? Once its forehead emerges.

הַמַּפֶּלֶת טֻמְטוּם, וְאַנְדְּרוֹגִינוֹס, תֵּשֵׁב לְזָכָר וְלִנְקֵבָה. טֻמְטוּם וְזָכָר, אַנְדְּרוֹגִינוֹס וְזָכָר, תֵּשֵׁב לְזָכָר וְלִנְקֵבָה. טֻמְטוּם וּנְקֵבָה, אַנְדְּרוֹגִינוֹס וּנְקֵבָה, תֵּשֵׁב לִנְקֵבָה בִלְבָד. יָצָא מְחֻתָּךְ אוֹ מְסֹרָס, מִשֶּׁיָּצָא רֻבּוֹ, הֲרֵי הוּא כְיָלוּד. יָצָא כְדַרְכּוֹ, עַד שֶׁיֵּצֵא רֹב רֹאשׁוֹ. וְאֵיזֶהוּ רֹב רֹאשׁוֹ, מִשֶּׁתֵּצֵא פַדַּחְתּוֹ: