Here is a close-up of the two arteries and one vein of the umbilical cord. The vein is the bleeding vessel.
Students often struggle to remember which has two, the arteries or veins. For some, repeating it over and over again (two arteries, one vein) is enough. I had to play a game in my head that said two is "better" than 1 and A is closer to the beginning than V; the best of both wins. I know, it sounds ridiculous, but however you can remember, please do. It's pretty important.
We always check to see if there are three vessels There are times when the umbilical cord has one artery and one vein (called a two-vessel cord or Single Umbilical Artery [SUA]). This can point to defects in the baby, but, often enough, doesn't tell us one thing measurable. I send babies to the Pediatrician within a couple of days of birth with the information about the two-vessel cord, but most times, it isn't an issue at all for the baby.
"Anywhere from half to two-thirds of babies born with single artery umbilical cord are born healthy and with no chromosomal or congenital abnormalities. Of the remaining babies with SUA, some studies suggest that about 25 percent have birth defects, including chromosomal and/or other abnormalities. These can include trisomy 13 or trisomy 18. However, the most common pregnancy complications that occur in infants with SUA are heart defects, gastrointestinal tract abnormalities and problems with the central nervous system. The respiratory system, urinary tract, and musculoskeletal system may also be affected. One in five babies affected by SUA will be born with multiple malformations."