Nida & Mikveh Purification after Miscarriage:[1]

If one had a miscarriage she is impure and is required to perform a Hefesk Taharah and count seven clean days. This applies even if she did not see any blood with her miscarriage, and had the miscarriage within 40 days of conception.[2] However, regarding the minimum amount of days she must wait prior to immersion in a Mikveh, there is a difference between a woman who miscarried within 40 days of conception versus one who miscarried after 40 days of conception.

Miscarried within 40 days of conception:[3] A woman who miscarried within 40 days of conception [meaning within 40 days counted from her last Mikveh night[4]] has the same status as a regular Nida, and not the more stringent status of a Yoledes, and hence as soon as she waits five days and has stopped seeing blood, she may perform a Hefsek Taharah and count the seven clean days and immerse in a Mikveh even if it is within 14 days from the miscarriage.[5]

Waiting a minimum of 14 days if after 40 days of conception: If she had a miscarriage after being pregnant over 40 days[6] [meaning 41 days counted from her last Mikveh night, as explained above] then it has the same status as one who gave birth.[7] Thus she may not immerse in a Mikveh until 14 days pass from the start of her miscarriage, even if she was successfully able to count 7 clean days before hand.[8] She may however already perform a Hefsek Taharah after 5 days and then count the seven clean days.[9] On the night of the 15th she can then immerse in a Mikveh. [If the woman had to go to a doctor to have her womb cleaned out[10], then the 14 days are counted starting from when her womb was cleaned by the doctor.[11] Practically most women bleed after miscarriages for several days and hence the above law of ability to immerse within 14 days is rarely applied. Furthermore, most women after miscarriage are advised not to be intimate for between 2-6 weeks from the time of the miscarriage in order to help them recover. Accordingly, the age-old custom is for women to wait four weeks before immersing in a Mikveh.[12] However, she should not delay immersion without justifiable reason.[13] Practically, one is to consult with a doctor and/or rabbi in this matter.[14]]

Vestos: A woman who miscarried after 40 days follows the same law as a woman who gave birth regarding suspecting for previous Vestos, as explained in Halacha 4C.[15] When a woman becomes a Nidah due to a miscarriage the date of the miscarriage is not marked on the calendar for the sake of having Vestos calculated from it.[16]

[1] Michaber 194:2-10; Taharah Kehalacha 11:11; Family Purity p. 175; Kitzur Dinei Taharah 14:3-4; Toras Hayoledes 38:7-10; Nitei Gavriel 112

[2] The reason: As in Pesichas Hakever Beli Dam. [Rama 194:2]

[3] Michaber and Rama 194:2; Nitei Gavriel 112:2

[4] Beir Heiytiv 194:4; Pischeiy Teshuvah 194:3; Taharah Kehalacha 1 footnote 22; See Nitei Gavriel 112:3-4 footnote 3 in length; See Meiy Nida Nidda 30 regarding if these days are counted as 24 hours each

Went to Mikveh for Rabbinical Kesem: However, this only applies if her Mikveh night was from a period cycle. If however her last Mikveh night was due to a Rabbinical impurity, such as a Kesem then she must count back to the last time she went to Mikveh due to a Biblical impurity, such as her period.

[5] Rama ibid

[6] If she has been pregnant exactly 40 days she is only considered a Nida and is not considered to have given birth. [Taharah Kehalacha ibid footnote 19]

[7] Michaber 194:2

[8] Michaber 194:3; Taz 194:3; Shach 194:4; Toras Hashelamim 194:2; Lechem Usimla 194:29

The reason: As perhaps the fetus was a female. In which case she may not immerse until 14 days pass.

[9] So is the implication from 194:1 and 3, and so rules Taharaha Kehalacha regarding birth; Family Purity ibid regarding miscarriage.

Other Opinions: The Shach [194:4] rules one must delay counting the seven clean days until 14 days have passed from the miscarriage.

[10] This is known as a D&C procedure, also known as dilation and curettage,

[11] Shevet Halevi 9:182; Nitei Gavriel 112:8

[12] Shaareiy Tzedek 136; Taharas Yisrael 136:4; Pischa Zuta 194

[13] See Chacham Tzevi 8; Daas Torah 194; Chasam Sofer 157; Nitei Gavriel 112:15

[14] Nitei Gavriel 112:14

[15] Sidrei Taharah 189:36; Pleisi 189:31; Pardes Rimonim Sifsei Chacham 189:73; Chidrei Deiah 189; Beis Shearim 259; Poseiach Shaar 2:16; Arugas Habosem 172; Nitei Gavriel 112:5; Taharah Kehalacha 24:100

Bedikos by Tashmish: See Shevet Halevi 186:2; Nitei Gavriel 112:16

[16] See Nitei Gavriel 112:12; Taharah Kehalacha 24:5; Shiureiy Shevet Halevi Hosafos Utikunim