As with much of the overly simplistic suggestions of non-traditional scholars and so-called bible critics, this explanation doesn’t stand up to closer scrutiny. If “inflated stomach” refers to a pregnancy and “fallen thigh” refers to a miscarriage, then the pregnancy obviously must come first. Yet, the first time the expression is used (5:21) the “fallen thigh” precedes the “inflated stomach.” Even if “inflated stomach” refers to something that happens inside to cause the miscarriage, it still would have to come before the “thigh falling” (the miscarriage). Although it is laudable to provide a more humane way of dealing with suspected adulterers than might have been the prevailing custom in ancient civilization (and unfortunately still practiced in some cultures), if the consequence of not admitting to sinning is “only” the loss of an inappropriately conceived child, there is little motivation to avoid getting into such a predicament or to admit wrongdoing in order to avoid the Soteh process. (It is also less likely that an incensed husband will be assuaged by being able to put her through a process with less than severe consequences.) And there wouldn’t be any consequences for her paramour (whereas according to the traditional understanding, they both would suffer embarrassing and severely painful deaths). Additionally, if the process was not divinely designed with the results divinely administered, even if the husband would now think the child is his, the wife would know whether or not she was faithful; a successful childbirth would make the religion a mockery in her eyes. Even if some would keep things to themselves rather than admit they were unfaithful just to dispel disproved religious myths, eventually the truth would come out. Therefore, as appealing as such an explanation of the text might be, the traditional understanding of the severe, frighteningly miraculous consequences (under the right circumstances) is much more palatable.
There is one aspect of the miraculous nature of the Soteh process, at least the way it’s described by the Ramban, that deserves a closer look. How can the Ramban say that “in all of the Torah’s laws there is nothing that depends on a miracle besides this one,” if he himself, describing the “tzora’as” that afflicts clothing and houses (Vayikra 13:47), says “this does not appear in nature at all.” That “the rain coming in its proper time” when we keep the Torah (Vayikra 26:4) or not coming at all if we don’t (26:19) is also miraculous is not an issue, as these are what the Ramban describes (B’reishis 17:1 and elsewhere) as “hidden miracles.” Since rain (and lack of rain) occurs naturally, even though it is “miraculous” when it occurs as a matter of reward or punishment via divine intervention, it is not an obvious miracle. What happens to a guilty Soteh, on the other hand, is an obvious miracle. If the “tzora’as” that afflicts clothing and houses doesn’t occur naturally, why isn’t it in the same category as the Soteh process?
Although Ramban categorizes these forms of “tzora’as” as miraculous (since they “do not occur naturally”), their appearance is not part of a “test” of the righteousness of the garment/homeowner. It may be the result of sin, but it did not occur as part of a process to test whether or not there was sin. When Sh’muel called for a thunderstorm during the wheat harvest (during which time it never rains) to prove that the people had sinned by asking for a king (Sh’muel I 12:17-18), as well as when the fire came down on Eliyahu’s altar on Mt. Carmel (M’lachim 18:38) to prove Who is the One True G-d, they were not only miraculous, but were also done within the context of a test. This is not the case regarding “tzora’as,” so aside from the possibility of being able to attribute it to mold, or to some naturally-occurring phenomenon that we were previously unaware of (thereby minimizing the impact of it “not occurring in nature”), its appearance in a non-test environment precludes it from being considered a “set miracle.” It might be miraculous, and it might be supernatural, but it is not a miracle that can be reliably repeated (i.e. testing to see if the house of a suspected sinner gets it). The Soteh process, on the other hand, when followed through, does include a “set miracle,” depending on it as the basis for the Soteh process, thereby setting it apart from every other “Torah law.”
As I have previously discussed (http://rabbidmk.wordpress.com/2012/10/11/parashas-bereishis-5773/), the Creator avoids doing anything outside the laws of nature whenever possible. The Talmud (Shabbos 116a, and elsewhere) discusses how important “shalom bayis,” harmony between husband and wife, is, as indicated by G-d allowing His name to be erased (dissolved in the Soteh waters) in order to make peace between them. Resorting to a “set miracle” for the Soteh process, something not done anywhere else in the Torah, further illustrates how high a priority it is.