No. No, no, no, no. Just NO.
First of all, if that were true then there would be no single mothers OR single fathers, no need for child support, no deadbeat parents and no absentee parents. Children don't cement a relationship - EVER. The only way to "cement" a relationship is for the two people involved in it to completely commit to each other, forsaking all others, to share mutual love and respect, and to have no desire to ever be with anyone else ever again. A child is a blessing, and the icing on the cake. Besides, any woman who gets pregnant for the sole purpose of keeping her man around is getting pregnant for the WRONG reason, and the child will be the one to suffer for it. Perhaps a decent guy will stick around out of duty to the CHILD, but certainly not out of duty to the woman. And why on earth would you even WANT a man who only stayed because of the child? Why wouldn't you want him to stay because of YOU?
And not everyone sees having a baby as a "lifelong commitment". I personally know a woman whose husband left her when she was four months pregnant, came back after the baby was born, got her pregnant again and then left again, at four months pregnant. He has since signed over rights to his children and has never made an attempt to be in their lives again. The world is unfortunately full of people exactly like him.