There are some who argue that pregnancy should be classified as a disease.

Arguments for this proposal vary, but the most common ones seem to be analogies. Like many diseases, pregnancy causes varying degrees of multiple different symptoms: nausea, headache, back pain, stomach pain, swelling among others.
Likewise, pregnancy, as do most diseases, proceeds if not treated, and usually resolves itself after a typical time period but can be fatal similarly to pneumonia, for example.
There is also a specific pathogen that causes the "disease" - sperm.

Another line of argument in support of classifying pregnancy as a disease relies upon a certain definition of health, much debated in itself.
This definition construes health as an overall wellbeing of an individual, rather than the more common, and traditional definition of health, which sees it as "normally" functioning body. If we embrace the former, it turns out that all suffering has to be a disease - that is, abscence of overall wellbeing. Pregnancy causes suffering, and therefore it has to be a disease.

Despite the latter two and other lines of argument have been presented, the core of the proposal seems to be pragmatic.
It is a widely accepted fact that all kinds of symptoms in women have been historically, and even now, downplayed and dismissed as "normal" and just a part of life. Such is definitely the case with pregnancy also.
Classifying pregnancy as a disease would make it harder for professionals to dismiss the symptoms and suffering experienced by pregnant women. It would probably also enhance the research efforts to come up with better treatment for pregnancy related symptoms. Maybe we would even come up with a treatment for migraine during pregnancy!

I am to argue here that despite the merits of the aforementioned arguments, pregnancy should not be classified as a disease.

1. Whatever kinds of analogies may be used to argue for the similarity of pregnancy and diseases, there is a problem. There are other biological states that could be similarly equated - puberty, old age and sorrow, for example, all cause many different symptoms and suffering, which, albeit usually less sevear than those caused by pregnancy, do not differ from pregnancy symptoms in qualitative way. Therefore such analogy as a base for this argument can only be used if at the same time one accepts classifying old age as a disease as well.

2. Definition of health as a state of overall wellbeing is precisely what leads to patients feeling dissapointed and medical professionals being exhausted. If health means that one feels good, than all suffering should be examined and treated. We can only treat a small proportion of things that cause suffering to humans. This leads to patients inevitably feeling disappointed, and that their suffering - "disease" - is not taken seriously.
This definition also turns the field of medicine into an all encompassing study of human existence. Whatever the problem may be, medicine is responsible for trying to fix it.
Physicians, moreover, are then transformed into technicians. The job of the physicians is to operate the enourmous machinery of medical knowledge and technology to produce whatever kind of value to each patient, regardless of whether the problem has anything to with biology or even psychology. That is exhausting. Health should thus be connected to some form of baseline normalcy regarding human biology. Critics argue that we are well passed teleological explanations, so such "normalcy" is impossible to define. That is a topic of another discussion. I am not making definite positive claims about health here - just refuting the one proposed by the proponents of the original argument.

3. However well-intentioned, pragmatism is ill-suited as a base for this argument.
The argument is of the form of: "historically downplayed, suffering causing X has to be classified as a disease, so that downplaying of X stops, and treatment of X is enhanced". Note that adding the term "biological" or "physiological" in front of "suffering" would evoke difficult questions of "normalcy" and essential characteristics of the human body - questions which are hard to answer for the proponents of the original argument for the aforementioned reasons.
Well and good, then, but insert "poverty" in the place of X, and ask yourself: are you willing to call poor people sick just because they are poor?