It looks like the study had a multi-pronged approach, but in terms of the mechanism of action, the study was focused more on the brain than the rest of the body, and the authors posit that the areas where the semaglutides are acting are resulting in decreased appetite.

The semaglutides are analogues of GLP-1 (glucagon-like peptide 1) which is released from cells in the intestine, with receptors in the body including in the pancreas, stomach, kidney, lung, heart, skin, immune cells, and the hypothalamus. It is one of the hormones involved in regulating blood sugar and digestion, partially through its regulation of other hormones.

So to sum it up, I don't think they just make you eat less, it seems like there's a hormonal/nervous system/gastrointestinal overlap in mechanism of action.

I think it depends - the pregnant women may or may not have persisting immunity against rubella.

If she does have immunity, then there is supposed to be protection from rubella, as there is a fraction of her rubella antibodies that is transferred to the fetal circulation through the placenta.

In Canada (or at least the province I'm in), it's routine to check rubella antibody levels in the a women's blood prior to or during early pregnancy, and see if they correspond to levels indicating immunity. The mother may have immunity from an actual previous exposure/infection with the virus, or from vaccination. There are certainly cases where the result has come back as no or indeterminate immunity, rather than suggestive of immunity.

Since the MMR (measles, mumps, rubella) vaccine is a live-virus vaccine, and the big reason to care about rubella in pregnancy is birth defects, the MMR vaccine is not recommended within a few weeks of starting to try and get pregnant, or during pregnancy.

All that said, I think the general recommendation is for pregnant women (immunized or not) is to avoid people with infectious diseases when possible.