@kaferty I can't find a free version of the full study. But I suspect they are grouping premies or complicated pregnancies/births with less complicated c-sections. Or maybe, they are just flat out wrong, it is a big and unusual claim. I honestly wouldn't stress about it.
Also to put it in perspective, the average rate of failure is about
1 in 100, so if you are doubling your odds, it ~2 out 100 chance of having a breakthrough infection. Base rate really matters in science.
On antibody testing, this is usually a blood test your doctor orders. But as a researcher who worked tangentially on COVID antibody studies, antibody tests are a mess and it require a lot of specialized knowledge into understanding what test is appropriate and what type of immunity can be determine. Your doctor may not be equipped to help you interpret your results effectively and at the end of the day, you will get a really expensive piece of paper that tells you nothing. I saw a lot of doctors giving the wrong test to patients during the acute stages of the COVID pandemic, telling them they had a past infection, when in reality, all it was detecting was if they had the vaccine, or sometimes they would give the wrong test that wasn't sensitive to long term antibodies and failed to detect past infections. There were dozens of COVID antibody tests and they all had drastically different efficacy in detecting antibodies. Maybe Measles is different because it is a well known disease, but any time antibody tests come up, I get very skeptical.