All the societal factors aside (which are huge) it remains that only women can have babies and breastfeed them. In itself, this means women will always need sometime out of the workplace, if not much, whereas men don’t need to take any time out. In itself, this will always have an impact.
The impacts become larger. Once a woman chooses to breastfeed me has had some time out of work, it often seems to ‘make sense’ for the remaining parental leave to be taken by that parent. Women then Return to the workplace after an absence of 6-12 months, often using accrued holiday for days out per week for child sick leave etc. The woman does not return in exactly the same way to the workplace, but as a mother who has an additional responsibility which takes time from work (sick leave etc) in a way it’s doesn’t for most men.
Women are more likely to return part time. This is a societal expectation that women do the childcare and a function of the fact women do the early stages whilst breastfeeding and the sense that the woman can do it and is good at it, whilst the man is less confident at it develops. So then the woman either returns part time or if working full time still take son more of the childcare planning and compromises, even when there is paid childcare. And if returning to work, there is likely to be a 2 nd pregnancy within 2-5 years, so further time when the woman is clearly pregnant and about to leave, or absent on maternity leave, or just returned from maternity leave. It is all noticed and viewed as reducing productivity and attachment to the workforce.
In basic economic theory, your marginal revenue product (the revenue you bring to your firm) determines demand for your labour and has a key role in your wage. Time out of the workforce for childbearing and rearing reduces experience in the workplace, so productivity. This is before any discrimination or lower perception of women who are mothers as workers, further reduces the perceived marginal revenue product.
Women taking time out of work to look after sick child or attend a child’s school sevent is seen as a bit of a pain and tolerated, whilst a man is seen as a jolly good bloke for doing it. Men are careful to do it very rarely in most cases which adds to its novelty value, and the majority of the ‘burden’ falls on women which builds the sense that employers have of women who are mothers being flaky or unreliable or uncommitted.
When the reality is that lots of women want to stay at home at least part time, the reality is that men being full time is more the norm. In itself, this means men get more experience and promotions. Make attachment to the workplace is stronger.....they have fewer gaps or time out in their careers and this is strongly associated with career progression.