Can you please break down the recommendation for babies to get back to their birth weight by two weeks? I’ve heard that birth weight isn’t great to go off of, and feels like it creates a lot of anxiety when people have been having babies without this recommendation for centuries.
—Momma
I can definitely attest to the anxiety produced by infant weight gain recommendations. Generally, these recommendations are intended as a way to quickly gauge if a baby is sufficiently gaining weight. It’s not intended as a metric, like “if this happens by day 14, great; if not, disaster.” Moreover, there is nothing special about birth weight — it’s a rule of thumb. In practice, though, it can often be presented as some kind of important milestone. What does the data say?
Although this general guidance has been around for a long time, data has been surprisingly sparse. Fortunately, in 2015, researchers published data from a very large sample of newborns (almost 150,000) that describes the patterns of weight loss and regain. This kind of data is quite helpful in seeing what is “average” and how much variation to expect in healthy infants.
In these data, the speed of weight gain depends on birth circumstances. Among those with a vaginal delivery, 50% of newborns had returned to their birth weight by 9 days, 86% by 14 days, and 95% by 21 days. Among those born via C-section, half were back to birth weight by 10 days, 76% by 14 days, and 92% by 21 days. The authors here were not able to distinguish feeding type, so they cannot comment on whether breastfed babies gain faster or slower.
Based on these data, the authors suggest that this older guidance — that babies should be back to their birth weight within a week — is outdated and does not capture the reality. Their data points to a sizable share of babies not returning to their birth weight even within two weeks, meaning that is not necessarily a cause for concern if the baby is otherwise well-seeming (is peeing, pooping, etc.).
If you are curious where your baby falls in the distribution, the authors used their data to create this website, where you can enter your baby’s weight and see where they fall along the curve.
The upshot: Weight gain is one metric that can be helpful in evaluating how an infant is doing, but many babies take over a week to return to their birth weight.
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My baby didn’t get back to birth weight until about 28 days. I was on IV fluids for 41 hours during labor and we both ended up incredibly swollen and full of fluids. He ended up losing about 12% of his “birth weight” (8lbs 13oz) by his first checkup and the doctors made it seem like it was def con 4. They even suggested he may have a metabolic condition prohibiting him from proper weight gain when in fact he was just peeing out all of the stupid fluids we were given. He was still a VERY healthy weight at 7lbs 15oz and we were forced to do weight checks nearly every day for two weeks. It was an absolute horror show and a terrible way to be introduced to parenthood. I will not be pressured in to daily weight checks should a similar situation arise in future babies. If I can help it I won’t be giving birth in a hospital again! The woods would have been a better option. 🙂