hello
i think you need to have a long think about what you want, when TTC i was at a point where i hated where i worked but the maternity package was good so i put up with it whilst TTC, we as a couple did not want to wait until i had found a new job and worked a year (usually the time you need to qualify for comapany mat pay)
it may not happen straight away, it took us 11 months, would you feel happier getting a higher position now or it taking a year to TTC and missing out? in hindsight i wish i had moved job, as it turned out i would have probably been in a new job long enough and could kick myself for not doing it but i suppose i though it would happen quicker. have you though about what you would do after the baby, i am going back part time and plan to improve my career when we have compleated our family and they are all at school, if you are planning to go back full time its not really an issue but if you want part time they may not be able to offer you your old position also if you take more than 6 months they dont have to give you your old job back just one at the same grade
there is so much to think about,
good luck