Some have thought that this doubling of each of the two periods was intended to remind the people of the fact that woman represents the lower side of human nature, and was the first to fall into temptation. 1-Timothy 2:13-15; 1-Peter 3:7. The ancients had a notion that the mother suffers for a longer time after the birth of a girl than after the birth of a boy. The period required for the restoration of her health in the one case was thirty days, and in the other, it was 40 or 42 days. This notion may have been connected with a general custom of observing the distinction as early as the time of Moses.

But if she bear a maid child, then she shall be unclean two (e) weeks, as in her separation: and she shall continue in the blood of her purifying threescore and six days.
(e) Twice as long as if she gave birth to a boy.

But if she bear a maid child,.... A daughter, whether born alive or dead, if she goes with it her full time:
then she shall be unclean two weeks; or fourteen days running; and on the fifteenth day be free or loosed, as the Targum of Jonathan, just as long again as for a man child:
as in her separation; on account of her monthly courses; the sense is, that she should be fourteen days, to all intents and purposes, as unclean as when these are upon her:
and she shall continue in the blood of her purifying sixty and six days; which being added to the fourteen make eighty days, just as many more as in the case of a male child; the reason of which, as given by some Jewish writers, is, because of the greater flow of humours, and the corruption of the blood through the birth of a female than of a male: but perhaps the truer reason may be, what a learned man (p) suggests, that a male infant circumcised on the eighth day, by the profusion of its own blood, bears part of the purgation; wherefore the mother, for the birth of a female, must suffer twice the time of separation; the separation is finished within two weeks, but the purgation continues sixty six days; a male child satisfies the law together, and at once, by circumcision; but an adult female bears both the purgation and separation every month. According to Hippocrates (q), the purgation of a new mother, after the birth of a female, is forty two days, and after the birth of a male thirty days; so that it should seem there is something in nature which requires a longer time for purifying after the one than after the other, and which may in part be regarded by this law; but it chiefly depends upon the sovereign will of the lawgiver. The Jews do not now strictly observe this. Buxtorf (r) says, the custom prevails now with them, that whether a woman bears a male or a female, at the end of forty days she leaves her bed, and returns to her husband; but Leo of Modena relates (s), that if she bears a male child, her husband may not touch her for the space of seven weeks; and if a female, the space of three months; though he allows, in some places, they continue separated a less while, according as the custom of the place is.
(p) Scheuchzer. Physic. Sacr. vol. 2. p. 314, 315. (q) Apud Grotium in loc. (r) Synagog. Jude. c. 5. p. 120. (s) History of Rites, Customs, &c. of the Jews, par. 4. c. 5. sect. 3.

But if she had given birth to a girl, she was to be unclean two weeks (14 days), as in her menstruation, and then after that to remain at home 66 days. The distinction between the seven (or fourteen) days of the "separation for her infirmity," and the thirty-three (or sixty-six) days of the "blood of her purifying," had a natural ground in the bodily secretions connected with child-birth, which are stronger and have more blood in them in the first week (lochia rubra) than the more watery discharge of the lochia alba, which may last as much as five weeks, so that the normal state may not be restored till about six weeks after the birth of the child. The prolongation of the period, in connection with the birth of a girl, was also founded upon the notion, which was very common in antiquity, that the bleeding and watery discharge continued longer after the birth of a girl than after that of a boy (Hippocr. Opp. ed. Khn. i. p. 393; Aristot. h. an. 6, 22; 7, 3, cf. Burdach, Physiologie iii. p. 34). But the extension of the period to 40 and 80 days can only be accounted for from the significance of the numbers, which we meet with repeatedly, more especially the number forty (see at Exodus 24:18).

Threescore and six days - The time in both particulars is double to the former, not so much from natural causes, as to put an honour upon the sacrament of circumcision, which being administered to the males, did put an end to that pollution sooner than otherwise had been.