From 50 Years Ago: The People of India (On the Census of 1961).

… Another matter which arrests attention is the deterioration in the sex ratio. Compared with a decade ago, when there were 946 fe-males for every 1000 males, there are now only 940 females. This ratio has fallen stead-ily since 1901 and is less than unity now in all the States except Kerala and Orissa. The ratio is the lowest in Punjab (868) amongst the major States; it is even lower in Delhi, at 786 females per 1000 males. …To the question of the declining trend in the sex ratio, a great deal of thought will naturally be devoted by the demographers. But there is to the simpleminded a possible explanation... [T]he measures which have reduced the general death rate have perhaps had an unequal incidence as between the sexes. The male population is not susceptible to a major cause of death amongst women, viz, child-bearing. The number of births per thousand of population is probably no less now than it used to be in the past. The trend towards urbanisation, the growth of the middle-class, greater knowledge of contraceptive measures, etc, might have caused some decline but not enough to be of any significance. It follows, therefore, that mortality connected with child-bearing re-mains more or less the same as in the past, and this vitally affects the sex ratio. That at least seems plausible and the position will become clear only when the relative death rate amongst women of child-bearing age is known.