The gemara makes reference to an angel that is appointed over conception. Tosafos raises a question from the gemara in Ta'anis 2a that says that the key to birth remains in the hands of Hashem and isn't entrusted to an angel. Tosafos HaRosh answers that Hashem deals with conception Himself, but then hands it off to an angel to take over. However, Tosafos seems to make a distinction between conception and birth. An angel is appointed over conception but Hashem Himself deals with the birthing process. This implies that we consider birth to be a greater miracle than that of conception so that G-d must deal with it himself.