Many expectant moms are eager to meet their new babies, but there’s a good reason to try to hold off labor until they’re full term. When children are born too early, it can have a major impact on their brain development — potentially upping their chances of experiencing psychological and behavioral issues later on in life.

During the last trimester, babies are working hard to grow as much as they can to prepare themselves for the outside world. To parents excited to greet their new family member, the last few weeks stretching toward the due date might seem to take forever — but that time is crucial for the brain to fully develop. Every day counts.

Research shows that the longer a baby is able to stay inside their mom’s womb, the more time their brains have to grow and strengthen. Kids who are born at full term (39-41 weeks) are less likely than babies born early — including those born early term (37-38 weeks), or preterm (at 36 weeks or before) — to have learning issues or be diagnosed with conditions like attention deficit hyperactivity disorders (ADHD). The earlier a child is born, the greater the difference of learning or behavioral issues compared to those born at full term.

During pregnancy, babies grow at a rapid pace. Even after ultrasounds start to look more like babies than adorable blobs, their bodies are working to grow their ever-expanding brains. During the last trimester, babies‘ brains grow by almost .25 cubic inches per week — making connections and fine-tuning their cognitive processes to help them learn, hold attention, and even maintain balance.

After they’re born, however, their bodies don’t continue to develop at the same rate. In fact, brain development slows down considerably. When researchers compared brain scans of preterm babies with those of unborn children conceived at the same time, they found huge differences in brain volume, signaling that development appears to get permanently disrupted when infants are born too early — something that could leave children with lifelong disadvantages compared to their full-term peers.

The biggest difference is in those who are considered very or extremely preterm — that is those born before 32 weeks — but even a few weeks can make a huge difference. Past research showed an unborn child’s brain is 50 percent bigger at 40 weeks than it was at 34 weeks. One large-scale study looked at children considered to be either early term or full term and found that the IQs of kids born at 37 weeks were around 3 points lower, on average, than those born at 39-41 weeks. This was true even when the babies were otherwise healthy, including being born at a healthy weight.

Of course, this doesn’t mean that many children born prior to 40 weeks won’t be as smart or as capable of learning as their peers. The numbers are based on averages and are not meant to be a prediction of how bright any one child will be. That being said, the results from these studies show how important it is for expectant moms to do what they can to help their babies make it to full term, if at all possible. Attending all your prenatal visits, eating a healthy diet, quitting smoking and drinking, and getting in some exercise can all go a long way to helping give your baby’s brain — and your baby — reach their potential.