It depends upon how well equipped you want to be.

For basic birthing it is fine. Long back seat with and head height
enough for raised knees etc., There are no cup holders, but plenty of
space for a bag of towels and a flask of water. (Cigar lighter socket
will power a heating element for the water). Boot capacity is fine
for holding a change of clothes, etc.,

For those wishing to be fully prepared whilst "having a baby", it is
difficult to see how AR166 would have room for every possible need.

Midwife, Obstetrics team incase of the need for a caesarian. Room for
incubator if the delivery is premature. Etc.,

Please remember that after the birth you will not be able to legally
move the car until the child has been wrenched from the mother's arms
and secured in an appropriate seat.

Pete