It is not unique to JW's but the phenomena appears to be a little more pronounced than any other Christian religion. Here is a bit of data I downloaded from the Aust 2016 census:
So 56.48% of JWs in Aust are women.
Interestingly, it does not start out that way. For some reason, the "Return to Jehovahs" (what I label POMIs who return to the Borg after having kids) are more likely to return if they bring a male child with them, than a female child. Here is the same chart, but only filtering out all those under 10 years of age:
It is an interesting phenomena. I have my suspicions why, but I will leave that to others to comment.
What happens after? I won't produce lots of charts, but essentially, boys outnumber girls, but as they go through the teenage years and early 20's, the boys leave in slightly greater numbers.
If I filter out everyone under 50 years of age (ie include only those 50 and above) the chart looks like: