Pregnancy-related event	Number of days after ovulation	Number of days after fertile mating
Onset of oestrus	-6 to +3
First of multiple matings	-7 to +5	-12 to 0
Fertile mating	-5 to +5	0
Ovulation	0	-5 to +5
Fertilization	2 to 5	0 to 7
Vaginal cornification reduced	5 to 7	0 to 12
Embryo attachment to uterus	14 to 16	9 to 21
Vesicles visible with ultrasound	15 to 17	10 to 22
Palpable 1 cm swellings	20 to 22	15 to 27
Foetal heartbeat visible (ultrasound)	22 to 23	17 to 28
Uterine swelling visible on X-ray	28 to 30	23 to 35
Palpability of swellings reduced	30 to 32	25 to 37
Earliest X-ray pregnancy diagnosis	43 to 45	39 to 50
Foetal pelvis visible on X-ray	51 to 55	46 to 60
Foetal teeth visible on X-ray	56 to 61	51 to 66
Whelping	62 to 64	57 to 69