nikhil had cancer and doctor told him that after chemo he might become infertile so they froze his sperm (sperm bank) before the chemotherapy. now he is cured of cancer and as doctor thought is unable to make his wife pregnant the natural way. so they tried artificial insemination with his sperm on tulika but she couldn't conceive. that's why they are going for surrogate mother.
so tulika is not infertile as artificial insemination doesn't always work for everyone.
the thing about being figure conscious is to just create hatred towards her. i believe that as women we all care about our figure but very rarely a women thinks about not having a baby. our serials and movies tend to show upperclass women as bad mothers which is untrue.