Ah. Yes. You...don't do it that way, do you. [Explaining reproduction is awkward. "When two Gallifreyans want an alliance very much..."]

We reproduce by artificially weaving genetic elements from two donors together and growing the resulting offspring in a loom chamber. Long ago, before Rassilon's time, we procreated much the same way as...well...as mammals do, but that all ended shortly after Rassilon came to power.