Will I be overlooked for promotion after having a baby: ask the expert

I am about to go on maternity leave and have been informed that my employers intend on a restructure. This is in response to my direct line manager who has found a new job and is about to leave the department. We have only just been through one restructure and the level of consultation was awful (decidedly lacking). I was lucky to be given a job I enjoy and a small pay rise. The woman who would be managing the restructure has made it clear to my manager that she does not believe I understand my own “feelings”, that when I have my child my work will become a low priority and I may well want part time work or flexible working. I am ambitious and would like a chance to progress, ideally I would like the opportunity to apply for my manager’s job. I am worried about two things: 1. If I were not pregnant then it is likely (although there is no way I could prove this) that the woman restructuring would apportion out the responsibilities (and some of the pay) of my manager’s role between myself and a colleague. I am concerned that she will pass on the opportunities for progression to my colleague and will not give my role any further responsibility as she thinks I will be too busy cooing over my child. 2. As she assumes that my ambition will disappear as soon as I have a child I am concerned that I will come back to a less responsible role, albeit, I am sure, one that gives me loads of flexibility. I also suspect that I will be managed by my colleague, who is less experienced than I am. If there is an opportunity for progression then what are my rights regarding applying for it during maternity leave? How can I argue with a woman who believes that I will gain crazy baby hormones as soon as my child arrives and will cease to care about my career? I am lucky, compared to your other posters as I do not currently believe that my job is at risk, but I do feel that I am about to be subjected to sexism (by my female! manager) and I don’t know how to fight it.