Is the Harm to the Woman or the Fetus?
The RSV renders the word ason> in v 23 as kill and attributes it solely to the mother. Other translations render it as “mischief”, “serious injury” or “harm”. That ason means some form of harm is well attested. Ason occurs only three other times in the Hebrew Bible.
3 Then ten of Joseph's brothers went down to buy grain from Egypt. 4 But Jacob did not send Benjamin, Joseph's brother, with the others, because he was afraid that harm [ason] might come to him.
38 But Jacob said, “My son will not go down there with you; his brother is dead and he is the only one left. If harm [ason] comes to him on the journey you are taking, you will bring my gray head down to the grave in sorrow.”
27 “Your servant my father said to us, ‘You know that my wife bore me two sons. 28 One of them went away from me, and I said, “He has surely been torn to pieces.” And I have not seen him since. 29 If you take this one from me too and harm [ason] comes to him, you will bring my gray head down to the grave in misery.’
The question is whether in this context it refers to harm to the mother. Some translations render the passage as “no further harm”. However, nothing in the Hebrew grammar demands this. In the Hebrew it is unspecified who the harm applies to and several arguments have been proposed suggesting that the harm is harm to the fetus and not the woman.
Westbrook argues that the word ason means “a disaster for which no one can be held responsible”. He then suggests ason is predicated of the child. Verse 22 deals with a case where one can assign responsibility and v 23 a case where one cannot. This interpretation has the added advantage of explaining the change from the third person “he shall pay” in v 22 to the first person “you shall pay” in v 23. In the first case the person responsible pays. In the second case, where the perpetrator is unknown, the whole community does.
The problem with this argument is that Westbrook’s claim that ason means “a disaster for which no one can be held responsible” is not well attested by the evidence. Moreover, as noted by Sprinkle several uses of ason in both the Hebrew Bible and in later Hebrew Apocrypha suggest the contrary. For example, the fear that Benjamin would be killed in Genesis does not have this feature. His brothers agreed to take responsibility and his execution by Egyptian officials is not an event in which one is unsure of who is responsible. In addition, Jacob believed a wild animal caused Joseph’s death so it is doubtful that ason carries the nuance that Westbrook suggests.
A second line of argument claims that the nuances of the word ason fit more naturally with the death of a fetus than the death of the mother. Kline argues,
A calamitous loss involving serious injury or even death is denoted by ason. In the only other Biblical context where ason is found it describes the grievous calamity that Jacob fears will befall Benjamin on the Journey to Egypt. (Gen 42:4, 38; 44:29). The choice of this unusual word in Ex 21:22 (problematic if the reference were to injury or death of the woman, for which the more common terminology would be expected) is readily explained if ason refers to the less everyday circumstance of the calamitous loss of offspring by violently induced miscarriage. 
[W]hy should an unusual word like aswn be used in Exod. xxi 23 to refer to death, when the ordinary verb mwt would appear to have served equally well? Fatal injuries are a common enough topic in the Misphatim, but on every other occasion the normal verb is used. There must be some reason why it is not used in Exod. xxi 22, 23. Part of the reason is that the word aswn, as is evident from the Jacob- Benjamin narrative, stresses the effect on the happening on some person other than the direct victim. Perhaps the best translation is “calamity”…
Had it [aswn] referred to the woman, it would be impossible to understand why the normal word for death was not used. But where a foetus is concerned, any hesitation to use the normal terminology of death is quite reasonable…We have seen that elsewhere it emphasizes the effect of the death or serious injury upon someone other than the victim himself. 
Moreover, both Kline’s and Jackson’s arguments suffer from the fact that the word ason is so rare in the Hebrew Bible that the samples they appeal to are too few to be decisive. The fact that the few references that occur have a special nuance is insufficient to ground an inference that this nuance is part of the meaning.
There is a more serious problem in attributing the harm as applicable to the fetus. The translation only makes sense if the passage refers to a premature birth and not a miscarriage. If the passage refers to a miscarriage then a miscarriage has occurred but the fetus did not die. This renders the text self-contradictory. I argued earlier that this text does refer to a miscarriage and that the premature-birth interpretation was subject to serious criticisms. In light of this, the argument ceases to be tenable. Once it is established that the text refers to a miscarriage the question of whom the mischief refers to is easily solved. If the blow has killed the fetus, it cannot be the fetus that is not killed in v 23. Further, if already dead, the fetus cannot be said to have undergone further harm.
From here I will address whether the punishments are qualitatively different. This will be split into two parts; the first will address whether the death of the woman is a capital offence, the second will ask if the text considers feticide a minor offence. The series will then conclude by returning to the question in the first part again asking, in light of the series, whether Harrison is correct in claiming that the Septuagint mistranslates the Hebrew?
 See K.J.V., N.I.V., A.S.B. respectively.
 Gen. 42:3-4, N.I.V.
 Gen. 42:38, N.I.V.
 Gen. 44:27-29, N.I.V.
 The New Living Bible renders the passage this way.
 Raymond Westbrook, “Lex Talionis and Exodus 21:22-25,” Revue Biblique 93 (1986): 52-69.
 Sprinkle, “The Interpretation of Exodus,” 7-8.
 Kline, “Lex Talionis and the Human Fetus,” 199.
 Jackson, “The Problems of Exodus,” 275.
 Ibid., 293.
 It can be objected that these few rare occurrences are all we have to go on and indeed they are, however, the best response is to note this fact and claim that we do not have enough evidence to make a decisive rendition. It is not sensible to infer that because insufficient evidence is all there is that one can go beyond what it justifies.
 A further point noted by Fuller in “Exodus 21:22-23:,” 172-173 is that a standard paradigm in some Ancient Near Eastern laws has a disjunction between a case where a blow is accompanied by a miscarriage and a blow where the woman is harmed or killed.
The Foundations of the Alexandrian Argument against Feticide Part I
The Foundations of the Alexandrian Argument against Feticide Part II
The Foundations of the Alexandrian Argument against Feticide Part IV
The Foundations of the Alexandrian Argument against Feticide Part V
The Foundations of the Alexandrian Argument against Feticide Part VI