This is most likely caused due to the following:
This is often the result of straining on the part of the hen, where large eggs are involved. It may also be the case with a pullet first coming into lay. Avoid giving pullets too much artificial light until they are well grown before the commencement of lay.If the shells have small spots of blood on them, rather than streaks, then suspect the presence of red mites. Treat with an anti-mite preparation from the vet or specialist suppliers.
Source: Broad Leys Publishing, http://blpbooks.co.uk/articles/egg_problemsI get bloody ones every now and then too. I was worried at first, but I think as long as it is a once and a while thing, and the hens are all acting okay and healthy, it is fine. Their plumbing is lined with a lot of blood vessels, so if one gets rubbed just the wrong way... I'm amazed that they don't bleed EVERY time they lay an egg, especially the big double yolk ones!
Exactly- the egg chute is lined with blood vessels and it's easy for a young layer to break one. However this is something you can do to help her, and your other hens. From time to time provide some oil or fat for them in feed or treats. Wild bird suet is good for this. This will enhance the feathercoat, add calories for winter and lubricate the skin and all membranes, including those in the egg chute. She will love you for this!
This hen may have been a little tense in the cold air- heat tends to dilate the chute. Just a momentary shiver could have popped a blood vessel. Please let us know if this clears up.
Source: Backyard Chickens Forum, http://www.backyardchickens.com/forumBlood spots on the yolk are not uncommon, even large one's. They are unappetizing but harmless to both the chicken and the cook. Blood covered yolk would mean an egg has been partially incubated and is unusable. As for the egg shell itself. Blood on the outside of an egg shell means the hen has popped a few blood vessels in the vent which is not unusual with a young pullet. The egg produced may have been a bit larger than she normally produces and ruptured vessels on exit. It is usually not a problem unless she continues to bleed long after laying the egg. If you can identify the hen that laid the egg you can ease things for her with a daily application of lubricant, even a little veggie oil will help her pass the egg cleanly. You will however need to make sure some of the oil gets into the vent about 1/2 inch inside. She will fuss and protest and it will take one person to hold her and one to administer the lubricant. You can dispense with this if the hen is indeed very young as it will correct itself within a few days. Remember to boost calcium and protein for these birds to encourage proper egg formation.
Source: Chicken and Roosters, http://wiki.answers.com/Q/What_can_a_blood-covered_chicken_egg_mean