I did not know Bengal's fertility rate was so low. And at the rate Bengalis are emigrating from Bengal, there will soon be drastic demographic changes there.
Yes it is, maybe the learnt something from Bangladesh, Bangladesh has been keeping a low fertillity rate too. Its gradually slowed down here thanks to NGO's etc Infact Bangladesh has made significant strides in HDI (Human Development Index) and has the best among south asian nations.
Bengalis in Bangladesh be talking about the innovations here to Bengalis in West Bengal and so the word spread through 'ADDA' (Something we bengalis love doing)