Do you have a source for this statistic? It is common practice in countries like China and India, to favor the birth of boys over those of girls. This has been exacerbated in China with the one child policy. After decades of the 'one child policy', the Chinese now recognize that giving birth to large numbers of boys necessitates the birth of girls, without whom, there is not future.
I’m assuming in the United States, not other non-western countries where females are considered less desirable.