This was originally posted on another thread relating to this topic and, I think, addresses the points you raise :
Here is another source for the story you are referring to:http://www.ananova.com/news/story/sm_514317.html
Oral sex makes pregnancies safer and more successful - study
New research suggests oral sex may not only help a woman conceive but may make her pregnancy safer and more successful.
The Australian study found that semen contains a growth factor which helps persuade a mother's immune system to accept sperm.
It claims to have found evidence that regular exposure before pregnancy, especially by mouth, helps her immune system get used to her partner's sperm.
Disorders during pregnancy often stem from the battle between the immune system and the foetus as a 'foreign body'.
Many of its 'foreign' proteins come courtesy of the father's genes so if the mother is regularly exposed to them her body is more likely to accept them.
Professor Gustaaf Dekker, from the University of Adelaide, said: "If there's repeated exposure to that signal then eventually when the woman conceives, her cells will say, 'we know that guy, he's been around a long time, we'll allow the pregnancy to continue."
New Scientist reports that Professor Dekker compared 41 pregnant women with pre-eclampsia, a condition where the mother's blood pressure soars during pregnancy, and 44 without.
He found 82% of those without the condition practised fellatio - only 44% of those with it did.
He says the protective effect was strongest if the woman swallowed the semen.
Now, when advising couples who have difficulty carrying pregnancies to full term, he says: "I tell them, 'semen exposure's good, and you could think of oral sex'."
"I never forget a face, but in your case I'll make an exception"
- Groucho Marx