The function of this change is to make the female pelvis able to function in childbirth, when the foetus is born through the pelvis. The space is called the 'birth canal'. There are many variations between one female and another in the structure of the pelvis. These differences have been studied in detail. These days by using ultrasound, the pelvis of pregnant women can be assessed to see if natural birth is likely to go ahead with no problems. The study is part of the medical speciality known as obstetrics.