2,124. Miscarrying in the First 40 Days

Hilchos Issurei Biah 10:2

If a woman miscarries in the first forty days of pregnancy, she is not rendered unclean for a birth; this includes the fortieth day itself. If a woman miscarries on the 41st day after marital relations, there is a doubt as to whether or not she has miscarried. She must therefore follow the rules that apply after the birth of a boy and a girl, as well as those of a niddah. If a human form can be detected in the fetus but it isn’t clear, she must follow the rules that apply after the birth of a boy and a girl. Such a fetus is called “well formed.”

Hilchos Issurei Biah 10:3

A well-formed embryo is as follows: when a human body starts to form, it’s the size of a lentil. The eyes are like the eyes of a fly, separate from one another, and the nostrils are like the eyes of a fly, close to one another. The mouth is open the width of a hair, while the hands and feet are indistinct. If it develops more than this but it still can’t be identified as male or female, we check it not in water but in oil, which will make it shine. One brings a wood chip with a smooth edge and uses it to examine the genital region from the top down. If the area is closed, it is identified as a male; if it looks like a split barleycorn, it is identified as a female and need not be checked. A woman does not have the leniency of pure blood for a miscarriage this undeveloped; rather, a fetus must have hair.