Doctors ask women who fathered their child and enters the name given on the birth certificate. If you are married to her and do not challenge that designation within a specified time (usually six months, in some states 90 days) then you are legally designated the father. If she divorces you and wants child support even if you produce results to show she is a cheating ho you will still be held legally and financially to be the father. The government does this because Mamas with no Babydaddys go on Welfare and the philosophy is better the cuckolded husband get saddled with the burden of supporting the drippings of another man's genitals than taxpayers. Most men don't think of challenging this designation. If they did it would be considered callous, untrustworthy, insulting etc. He might have no reason to suspect. Why would he ask for a special test of DNA which is not routine? When you apply for a marriage license you have to show a negative VD test so why not just make DNA tests required before a Father's name can be entered since the stakes are so high?
Yada I don’t ever plan to marry again. Much better to hookup. Marry them and you have to buy their crazy. Right now I have variety none of the downsides.