https://www.medpagetoday.com/infectiousdisease/covid19/85965
Pregnant women basically puts the cap of the upper age at around 40. This disease the virus causes in the body is very much worse for those that are older.
The study tested pregnant women admitted to the hospital to give birth. There are a lot of doctor appointments and lab work to check things in their last trimester. So they could've contracted it through those high risk places or routine contact with health care workers who I would say are also high risk.
Still, the study showed on admission that they were positive so they probably didn't get it from the hospital, unless on admission actually means some time after. That assumes it might be able to be detected so soon into the infect as well. It is a bit strange in that regard that it is such a high number.
That letter cites an article[2], which found that of the 43 pregnancy patients who tested positive, 14 (32.6%) were asymptomatic when admitted. However, 10 of them developed symptoms during their stay in the hospital or shortly after being discharged. It doesn’t say how long they tracked patients, but at most, 4 of the 33 could have been asymptomatic.
IMHO, the letter is confusing at best, but more likely intentionally misleading. FWIW, I probably would have come to the same conclusion had I not spent ~45 minutes digging through citations...
[1] https://www.nejm.org/doi/full/10.1056/NEJMc2009316?cookieSet... [2] https://www.sciencedirect.com/science/article/pii/S258993332...
1) The main cause of infant death due to coronavirus seems to be complications from early labor and the baby being premature. Also related to hypertension in the mother. But it's only the leading cause due to lack of other causes, not necessarily because it's common.
2) Pregnant women also have a non-standard, somewhat suppressed immune system, since they're basically tolerating a (half-)foreign 9-month infection of sorts. It also explains, as you mention, being vulnerable to various types of infections.
But if one of the causes of death for covid is cytokine storm, which is basically an over-responsive immune system failing to regulate itself, then it makes sense that pregnant women, with an over-regulated immune system, might have less risk from that aspect of the disease.
More info on it if you look at theories on placental development and why women are more susceptible to autoimmune diseases. Pretty fascinating stuff.