Though your post is a little bit lengthier, it lacks some essential details.
First, you have not mentioned your views about your being placed on the PIP for one month following the completion of 6 months period from the date of your joining. Had your performance been satisfactory, normally you would have been confirmed by the second week of May,2017. Any indication in the mean time from the Management about your under performance prior to the letter placing you on PIP effective from July4,2017? In the absence of any negative feed back about your performance before completion of the 6 months probation period, the decision of the Management to place you on PIP in view of your unsatisfactory performance after a lapse of almost two months that too after getting informed about your pregnancy in July,17 is certainly indicative of their intention of sending you out in order to deny your statutory maternity benefits. Therefore, they have terminated your services w.e.f 15-09-2017 couched in nice words. Since you were in supervisory or managerial cadre, no point in agitating against the merits of your termination.
Second, whether you informed the fact of your pregnancy formally any time before your termination?
Had you done so, the termination can not deprive you of your maternity benefit or medical bonus as per sec.12(2)(a) of the Maternity Benefit Act,1961, if it is applicable to the establishment. If so, you can make an appeal u/s 12(2)(b) of the MB Act,1961 within 60 days from the date of termination to the Inspector under the Act for the area to decide the question of maternity benefit.
From India, Salem