Women generally were constructed as being more caring and nurturing by nature. Women who worked were expected to give up work when they got married and men's wages were set at levels to support a family. A woman's role was in the home raising the family, and also caring for other adult dependents such as parents.
Of course it is well known that the process of raising a family is highly satisfying for women, because they are fulfilling their 'natural' instinct of caring for others, be that their children or other dependents. So women are best placed to take on a caring role.

Single women were dually constructed as angels/demons.  Think of associations with 'spinsters' - nasty, evil, interfering.  But women are natural carers, so they are also the angels that take up domestic service and look after wealthy people's children.  

The line of thought was that a single woman needed to sublimate her sexual urges by diverting her energy to caring for others and if she didn't have her own children, this process of sublimation could be achieved by looking after other people's children.  Many women were forced to go into domestic services if they weren't married (surplus of women due to the 'lost generation' of men in the war.)

Single women were also expected to look after their parents as they became older and indeed many couples would 'keep' usually their youngest daughter for this purpose and marry the rest off. So single women were able to live a happy and fulfilled life free of frustrated sexual desire by caring for other people.

But this also extended to 'spinsters' who took on roles as midwives and sort of social workers, which in itself was something of an extension on the philanthropic work done by middle classe women attempting to bring morality and Jesus to the unwashed masses of deviant working class women.  So single women eventually became constructed as experts on childbirth and child rearing.

And that, Colman, is why single women who have never had children are more entitled than you to offer their opinions on childbirth and child raising.  Consider it a hangover from the last century.  

The day I am no longer discriminated against in employment for being a woman, be it through wage differentials, assumptions about the worth and value of jobs that women do, or gender roles restricting my choice in the place I take up across the work/home divide; is the day that you can have an opinion about childbirth.