Mishnah Niddah 3:6: If she miscarries, and it is unknown what it is, 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 it is unknown whether it was a fetus or not, 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, and for [being] a niddah [a female who has menstrual discharges which render her impure; i.e. she should be stringent in all directions].

הַמַּפֶּלֶת וְאֵין יָדוּעַ מַה הוּא, תֵּשֵׁב לְזָכָר וְלִנְקֵבָה. אֵין יָדוּעַ אִם וָלָד הָיָה אִם לָאו, תֵּשֵׁב לְזָכָר וְלִנְקֵבָה וּלְנִדָּה:

Mishnah Niddah 3:7: If she miscarries on the fortieth day [since her prior immersion], she need not be concerned that it was a fetus. If [she miscarries] on the forty-first day, she should sit [for the required number of days] for a male and for a female, and for [being] a niddah. Rabbi Yishmael says: on the forty-first day she should sit for [the required number of days for one who gives birth to] a male and for [being] a niddah. On the eighty-first day she should sit for a male and for a female and for [being] a niddah, because [the formation of] a male is completed in forty-one [days], and a female in eighty-one. And the Sages say: this and that [are both completed] in forty-one.

הַמַּפֶּלֶת לְיוֹם אַרְבָּעִים, אֵינָהּ חוֹשֶׁשֶׁת לְוָלָד. לְיוֹם אַרְבָּעִים וְאֶחָד, תֵּשֵׁב לְזָכָר וְלִנְקֵבָה וּלְנִדָּה. רַבִּי יִשְׁמָעֵאל אוֹמֵר, יוֹם אַרְבָּעִים וְאֶחָד, תֵּשֵׁב לְזָכָר וּלְנִדָּה. יוֹם שְׁמוֹנִים וְאֶחָד, תֵּשֵׁב לְזָכָר וְלִנְקֵבָה וּלְנִדָּה, שֶׁהַזָּכָר נִגְמָר לְאַרְבָּעִים וְאֶחָד, וְהַנְּקֵבָה לִשְׁמוֹנִים וְאֶחָד. וַחֲכָמִים אוֹמְרִים, אֶחָד בְּרִיַּת הַזָּכָר וְאֶחָד בְּרִיַּת הַנְּקֵבָה, זֶה וָזֶה לְאַרְבָּעִים וְאֶחָד: