More men or more women? 男人多还是女人多？
"and infanticide, it happens but would be that big amount cases everywhere?"
Well, let's assume official statistics are correct and that there are 30 million more men than women in China.
That means about 20 million baby girls or female foetuses have been terminated during the last 30 years.
The best option for parents who want a boy is be an illegal CT scan - for those who can afford it. Those who have no access to the procedure or who cannot afford it can opt for infanticide. As you point out, in rural areas killing your baby daughters or leaving them unregistered is the only option.
China is roughly 50% rural and 50% urban so we are looking at an upper limit of about 10 million baby girls killed by their parents within the last 30 years. That number should be reduced by the 小黑户, which of course is impossible to know.
The current census has been astronomically expensive so presumably will provide the most authoritative figures on China's population.