Progesterone levels rise during your bitch’s heat. LH peak (luteinizing hormone) that set´s the ovulation in action often comes around day 9-15. A couple of days after this her eggs are ready and she is ovulating. This is indicated by the rise of the hormone progesterone. It is right time to mate her.
When a bitch is pregnant, her relaxin hormone levels rise. Relaxin is hormone produced by the placenta, therefore indicating that she is in whelp.