Nishmat's Women’s Health and HalachaIn memory of Chaya Mirel bat R' Avraham

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Endometrial Receptivity Assay

23 July, 2016


My husband and I have been going through fertility treatment in an attempt to have our first child. After four IVF cycles and three failed frozen embryo transfers including one miscarriage, our doctor suggested a new test called Endometrial Receptivity Assay (ERA), which is basically a biopsy of the uterine lining in an attempt to narrow down the transfer window and hopefully result in a successful transfer and pregnancy.

This procedure is time sensitive and will be done during my tahor weeks. My question is if there is bleeding as a result of this procedure, does that make me a niddah automatically because I would know it’s uterine blood? Or can I wear dark underwear and “not look” to avoid becoming niddah?


We are sorry to hear of your challenges conceiving, and of your difficulty with transfers and recent miscarriage.

Uterine bleeding will almost always result from an endometrial biopsy. Since this bleeding is caused by injury, the opinion of the posek of this site, Rav Yehuda Henkin, is that it does not render the woman niddah. The bleeding may go on for about a week, and for that time can be attributed to the procedure. Some other authorities are less comfortable permitting bleeding that comes from the uterus, even if a clear source of injury is seen.

For all procedures that enter the uterus, the size of the instrument inserted is also important. Instruments larger than a certain size render a woman niddah even if there is no bleeding. According to Rav Henkin, as long as the catheter used for an endometrial biopsy is less than 19mm in diameter, its entry into the uterus would not itself make you niddah. The catheter used for this procedure is typically smaller than this, though you should check with your physician.

We do recommend wearing colored underwear so as not to raise questions unnecessarily.  For more information on minimizing questions, please see our site’s articles “Stains” and “Toilet Paper“.

You may also find it helpful to consult a Yoetzet Halacha Fertility Counselor. (This is a free service, details here.)

Please feel free to get back to us with any further questions.

We wish you a successful procedure.

Response updated October 2020.

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