Can insurance company reject supplementary insurance because of potential pregnancy?

The insurer will be able to tell you that, they may have an opinion on that test/Behandlung. Always best to check that before you sign anything.

Pregnancy is not an illness and as many have said, also covered well by basic insurance.

No, the possibility of a pregnancy should not in itself be a reason for rejection.

I had a cardiac procedure some years ago back in Belgium, I disclosed this when I applied for supplementary insurance and the insurance company asked for more information. After receiving this information from the Belgian doctor my application was approved.

On the other hand the wanted to apply exclusions to the dental insurance policy which meant I would be paying the premiums for relatively little cover so I didn’t take them up on that.

Just explain that you're in the early stages of family planning and are having some tests done. Don't go overboard with information, keep it simple.

As said before, I think the reason to exclude is if they think you have a pre-existing condition that's going to cost them an arm and a leg, not just that you'll get pregnant. Insurance companies know that women can become pregnant, which is why supplemental insurances usually exclude pregnancy during the first year of the supplemental coverage.

Don't kid yourself, you pay for it that is for sure, maybe not directly but certainly indirectly

I was refused the supplementary insurance due to an pre-existing illness.

In the end: if I calculate what I would have paid more over the years and compare that to the upgrade I bought when I had an operation, I know what was financially the best deal

If an insurer were to accept you, they still would not likely cover costs related to an existing pregnancy because it would be considered a preexisting condition. Some policies also have qualification periods for maternity benefits.

As noted by others here, the basic compulsory health insurance provides pretty good coverage for maternity. All newer hospitals in Switzerland generally only have semi-private wards, so extra semi-private hospital insurance is pretty much a hangover from a past in which you were actually likely to share a room with 3 other people.

I wish you all the best for you and your baby.

This effectively happened to me. I took private insurance with Assura when I moved to CH in 1994 aged 34. I had no children and Assura (or the salesman) was concerned that I would be likely to be starting a family.

The restriction imposed on me was that I had private cover until the moment I entered a hospital to give birth, and then the supplementary cover kicked in again as soon as I left the hospital. Obviously apart from foregoing giving birth in a private hospital, which was of no real consequence to me, I could not have my Obstetrician nor my Pediatrician attend whilst I was in the hospital. In reality, although pretty unfair as I had had private cover for more than two years before my first pregnancy, it didn't make a great deal of difference to me as I would not have chosen a private hospital for birth due to the lack of special baby care units, and was immediately under the care of my chosen specialists immediately before and shortly following birth.

As mitigation, no one I encountered, from the Obstetrician, the Pediatrician, the hospital and midwife and other help I had following the births of my children had ever heard of this type of restriction before. As far as my memory serves though, it was a decision purely based on my age.