Look, lady, there are somewhere 200,000,000 to 500,000,000 little wigglers in the average ejaculation.
If there is a pregnancy, only one of those got through. One in half a billion. Think about that.
Tell you what, close the border to have a similar rate of eliminating illegal alien entry, and we can discuss the 'little things'.
The illegals are considerably larger, and should be easier to spot (barrier methods are pretty effective, as long as the means to stop leaks from getting through exist and are used.)