Matters which take time may be done before she reaches the Halachic state of a Yoledes: 
Calling a midwife: However to call a midwife from place to place which is a matter which takes time and delay is permitted to be done prior to this [i.e. to her reaching the above mentioned state of a Yoledes] from the time that she feels a little [need to give birth], even if she is in doubt.
When may one call an ambulance or drive to the hospital if he suspects his wife may need to give birth?
From the time one suspects his wife needs to give birth, even if she has not yet reached the Halachic state of a Yoledes, one may call an ambulance or drive her to the hospital.