Promotion during pregnancy

Presently i am working as Asstt.Supdt.of Gardens in Municipal Corporation of Greater Mumbai where i joined as Hort.Asst.on 1 Oct 1996. i was promoted from Hortt Asstt.to Asst. Supdt.of Gardens(4400 gradepay) and the order to this effect was issued on 11 August 2014. when i was promoted by my office, i was on leave w.e.f. 15 July, 2014 due to threat of abortion and i was blessed with baby girl on 30 Jan 2015 and then continued with maternity leave till July 2015. My office seniors said that as I was on maternity leave, I will not get benefits of promotion wef order issue date. As per them, my promotion benefits will be effective from that date of joining after ML that means date of accepting promotion only. i understand that maternity leave is a kind of leave which contains all sorts of benefits to the women employee in the manner as it should be for the person who is in continuity of the service. in view of the above, i would request you to kindly provide me copy of the related rules, regulations and oms for central government employees, so that i may pursue my office to get the promotion benefits and other dues with the due date i.e. April 01, 2016 accordingly .