The answer to this is no. such an egg is not kosher as can be seen from Kosher Eggs
The prohibition of eating blood applies even to the smallest drop of
blood, and thus any blood spots found in an egg renders the egg
non-kosher.
Each egg should be opened into a clear dish or glass and checked for
blood spots before it is cooked or combined with other food. If a
blood spot is found, the whole egg must be discarded, and the cup or
dish should be immediately and thoroughly washed with cold water.
When boiling eggs, it is customary to boil at least three eggs at a
time. Some people have a separate pot just for boiling eggs.
If a blood spot is found in a boiled egg, the whole egg must be
discarded.
Thus once the egg has been fertilized and the chick develops enough to show a "blood spot" the egg is not kosher. This is well before the embryo has developed enough to be identified as a chicken. Note that Eggs and Blood Spots does deal with modern non-fertilized eggs that might develop a blood spot.
It is in light of this modern reality that Harav Moshe Feinstein,
zt”l, (Igros Moshe, Yoreh Deah 1:36), clarifies that blood spots found
in commercially produced eggs do not present any fundamental kosher
problem. With respect to fertile eggs in the past, where a significant
doubt existed that the blood might represent a new embryo, it was
necessary to throw out the entire egg if it had a bloodspot. This is
also the reason why a minimum of three eggs were boiled at one time –
if one of them had a spot, it would be batel b’rov to the other two.
Today, however, the only concerns are maris ayin or dam beitzim (a
small amount of blood from a broken blood vessel in the hen, which is
not forbidden). As a result, the entire egg is never assur and
mei’ikar hadin removal of the blood spot would suffice. Moreover,
since the issur is not intrinsic to the egg, there is no problem with
cooking a single egg in a pot. Rav Moshe, however, writes that it is a
proper practice to dispose of the entire egg even today, as eggs are
not expensive and a person does not incur any significant loss.
Therefore, the requirement to check each egg remains in effect, as
does the requirement to dispose of eggs containing actual blood spots.
Nevertheless, in cases of doubt, difficulty or error, eggs are kosher,
even if checking was not done properly; moreover, if blood spots are
discovered during or after cooking, there is no problem with the
preparation utensils.
Note: Fertilized eggs are available in the marketplace and are sold at
a premium. When purchasing organic or natural eggs, a consumer should
be careful to check the carton and/or contact the egg producer.
Consumers wishing to consume fertile eggs should consult a competent
Posek for guidelines. Some kashrus agencies will not certify eggs that
are intentionally produced as they were in the past, because of the
halachic complexities pertaining to those eggs.
