When you're pregnant, getting proper nutrition is crucial. After all, the process of growing a baby takes a lot of energy, so you're probably loading up on fruits, vegetables, and other fresh foods. With that in mind, an unexpected source of nutrition may also help you maintain a healthy gestation. Knowing the benefits of swallowing sperm during pregnancy may convince you to indulge in certain activities.
As far as pregnancy activities are concerned, swallowing semen falls under the "won't hurt, might help" category. According to the Mayo Clinic, giving or receiving oral sex is safe during pregnancy. As long as the gestation is progressing without any health complications, a little oral fixation should not hurt. As always, ask a doctor about the safety of any activities that cause concern.
Now for the fun part: sperm consumption could benefit pregnancy in two major ways. First, swallowing sperm is associated with a decreased risk of preeclampsia, according to a 2000 article in the Journal of Reproductive Immunology. As put forward by the study, a pregnant woman's risk of preeclampsia is somehow affected by the fetus's paternal cells. By ingesting sperm, the woman may develop a tolerance against preeclampsia. (It's similar to an allergy shot, perhaps?) For what it's worth, additional research is needed to flesh out this theory. If you're into oral, though, it's a good reason to continue these activities throughout pregnancy.
A similar line of thinking applies to the second factor. As SUNY-Albany psychologist Gordon Gallup speculated, the mother's body might view the father's semen as a foreign object, and this could cause morning sickness, as noted in Slate. But by acquainting her body with the father's semen on a regular basis, via vaginal or oral sex, she may develop a tolerance to it. In effect, a blow job could help ease morning sickness. (Maybe.)
Feel free to contribute your own research to test these hypotheses. Hey, it's for science. And overall, swallowing sperm might ward off preeclampsia and reduce morning sickness for some people. At the very least, it's a reason to indulge in some adult fun before the baby arrives, so go right ahead if that sounds like the best kind of taste test.