Babies are born.
If Allah didn't permit sex, how would new (babies) Muslims come along?
Around week 20.
There is no way to determine the sex of an unborn child by the fetal heart rate that has been proven.
18 weeks, if your baby is cooperative
Roughly 20 weeks pregnant
In India there was (and is) a great desire to have sons. Ultrasound imaging used to determine the sex of an unborn baby was therefore a cause for the abortion of many female babies. Therefore the use of ultrasounds to determine sex was outlawed.
If you have sex you will
Autosomes do not determine the sex of the individual. Sex chromosomes do determine the sex of the individual.
Standing on your head. These are all fairy stories. Current research suggests that the position does not determine the sex of the baby and neither does it guarantee a baby.