Male dwarves appear to be incompatible hosts for the parasitic stage of dwarven development. Seperated from the host, the infant usually perishes quickly from lack of material sustenance.
Dwarves do not appear to lactate, as they do not appear to have any mammary tissues defined in the raws to substantiate the production of this nutritional source. This clearly indicates a more direct parasitical relationship, which explains why female dwarves are able to "hold" their infant while having both hands engaged in brutal combat, or otherwise occupied.
Once the offspring reach 1 year of age, the parastic phase ends, and the ambulatory menace stage begins, and persists for another 11 years.
After this 1 year point, mothers need to be monitored, as they have been sensitized to their reproductive partner's sprorulent emissions, and will continue to bear offspring as long as the male counterpart remains alive. (The spores are very tenacious things, by all accounts. Levels of separation capable of containing even forgotten beast deadly dust syndrome infections are no match for dwarven reproductive spores.) Additionally, some appear to be more strongly sensitized than others, and will bear many times as many offspring within any given sample interval given enough time to measure and establish trends.
While some overseers consider the parasitical stage dwarf offspring to be a valuable "Added layer of protection", others consider this practice abhorrent, and callous. Your mileage may vary.
Why hasn't toady implemented temporary sterility on an ingested syndrome for some surface plant types yet? This would resolve the issue nicely.