When pregnancy of a defendant is alleged as the cause for not pronouncing the death sentence, the court shall postpone the pronouncement of sentence until after it has decided the truth of that allegation. If necessary in order to arrive at such a decision, it shall immediately fix a time for a hearing to determine whether the defendant is pregnant and shall appoint not exceeding 3 competent disinterested physicians to examine the defendant as to the defendant’s alleged pregnancy and to testify at the hearing as to whether the defendant is pregnant. Other evidence regarding whether the defendant is pregnant may be introduced at the hearing by either party. If the court decides that the defendant is not pregnant, it shall proceed to pronounce sentence. If it decides that the defendant is pregnant, it shall commit the defendant to prison until it appears that the defendant is not pregnant and shall then pronounce sentence.