We sure wish there was another word for newborn jaundice, something like “the glow.” What is newborn jaundice and why do all babies experience it to some degree?
The answer lies in the story of a fascinating molecule called bilirubin, a brilliantly yellow pigment. Bilirubin belongs to a family of molecules called heme. The heme molecules make our world colorful. All the green of leaves (chlorophyll), all the red of blood (hemoglobin), and many of the bright hues of fall come from heme.
The bright yellow bilirubin is a breakdown product of the red hemoglobin. In almost all mammals old hemoglobin is processed into a gorgeous blue biliverdin, the color in robins’ eggs. Biliverdin is a very well-behaved molecule, it dissolves easily in water and is eliminated simply by peeing it out. But for unknown reasons, just about only humans take their biliverdin and turn it into bilirubin before getting rid of it. Bilirubin is not dissolvable in water so it has to be taken to our liver and twisted a bit before it can be dumped, in our stool. It’s the yellow bilirubin that makes newborn stools yellow, and broken down bilirubin in our stools makes our stool brown. If some biliverdin escapes conversion to bilirubin, that touch of blue in an newborn stool turns it from yellow to green. That’s why yellow, green, and brown are normal colors for poop.
It takes humans a lot of energy to make bilirubin, and to process it for elimination, why go to the bother? No one knows for sure, but Dr. Anthony McDonagh, who has written six volumes on the compounds of bilirubin and its relatives, notes that bilirubin is a very potent anti-oxidant. All these brightly colored heme molecules are electronically very active, that’s how they work to carry oxygen and why their color is so brilliant. The theory goes that bilirubin helps blunt the corrosive power of oxygen.
Now back to the newborn. During pregnancy, all the baby’s bilirubin is cleared by Mother’s liver via the placenta. But when the cord is cut, it is up to the newborn to clear out the bilirubin. But a newborn liver doesn’t really start doing this well for 2 weeks. It’s not explained by the process being complicated. All newborns transform their chemistries across thousands of reactions right at the moment of birth. There appears to be some value in holding off clearing the bilirubin for a few days. This is another place Dr. McDonagh’s thinking comes into play. When we are born, our level of oxygen in our blood really booms. We walk around with about 100 units of oxygen in our blood, fetuses have about 25, a level we could not live at. So at birth, the amount of oxygen goes up about 4-fold! One thought is that bilirubin accumulates to protect the newborn from the sudden surge in oxygen.
The result of 2 weeks of the newborn’s liver gearing up to clear out bilirubin is that every baby born sees a big rise in their bilirubin level, every. We should never have our bilirubin level go over 1. For us, a level over 1 means something is wrong with our liver, it is jaundice. But every baby born goes double over that level, everyone goes over 2, and millions go over 5. When you go over 5 you turn yellow. I would propose that something every human does is normal, and it is indeed normal, and very likely helpful, for newborns’ bilirubin levels to go well over our normal limit.
For healthy, full-term infants, it is not clear if there is a level of bilirubin above which harm occurs. This has been a focus of discussion amongst newborn medicine specialists for the last 70 years. But one recent study found that looking at children many years after birth, no harm could be detected from any bilirubin level under 35! We never let bilirubin levels get that high, but it’s nice to know that so many children who have been tested at such an extremely high level were found to be fine.
The stance of the Newborn Nursery, and How best to Understand
Given the normal nature of rising bilirubin and turning yellow after birth, which peaks around 3-5 days of age, just as you are going home, what is the reaction of most hospital’s nurseries to the yellow glow of the newborn?
Mostly it is very relaxed. Most nurseries are fine with bilirubin levels going up to, but not beyond, 20. But recently nurseries across the US have begun to plot the course of your newborn’s bilirubin level, and now if there is indication of a trend towards risk of exceeding 20, the nursery staff will raise worry.
A trend towards risk is very different than having a problem though. We have seen hundreds of newborns jump their bilirubin level rapidly in day 1 and 2, only to find they never come close to the threshold of 20. Their first bilirubin levels might raise question of a worrisome trend, but they almost all fail to have the worry materialize.
We recommend that the starting point for seeing your newborn turning some hues of yellow be reassurance. The accumulation of bilirubin is universal, it is harmless, it may actually be helpful. We watch the trends of your newborn’s bilirubin levels in the nursery carefully and would of course let you know if a problem actually develops. But that a rare occurrence, so if no problem actually emerges, we will recommend you enjoy the glow and not pay too much attention to the excitement the normal rise and fall of bilirubin now causes in most American nurseries.