Read internet discussions about homebirth, and you will often see statements such as "our hospital is five minutes away", or "it would take us 20 minutes to reach hospital". I would advise any family planning a homebirth to check the accuracy of this.
There are several things you need to take into account:If you call an ambulance, the call and the time it takes for the ambulance to get there are valuable moments. You may want to check the time it takes for an ambulance to actually arrive at your house. Don't take anyone's word for how long it takes to reach the hospital. Drive there yourself to check this. An ambulance will be quicker, but not all transfers happen in an ambulance. The hospital may have a check-in procedure that requires time. The ER is not always a good place to receive emergency maternity care. You'll need the actual maternity ward for the best care.
Preparation is always good with these points, we don't mean to be alarmist or to tell you that homebirth can't be safe. I had two homebirths myself, and they went very well. But unfortunately, it is not always possible to predict outcomes in advance, and knowing what to expect from a transfer is certainly useful. In addition, you might like to check the hospital's policies, and write a birth plan that would enable you to retain a certain level of control even if you do end up transferring.
If you have a back-up OB, you can discuss the procedure with them. Your midwife will also be a useful guide in this.