For many expecting couples, finding out the sex of their baby is a milestone. It can signify the color of the clothes they buy, their nursery decor, and their choice of name. But it also has the potential to prepare parents and providers for the likelihood of a more difficult pregnancy.

Although it varies from country to country, Europeans are typically on the taller side, and Asians are on the smaller side. In most cases, men are larger than women in both height and weight. The average height of a man is 5’8, while the average height of a woman is 5'3. In some cultures, having a son is seen as preferable, a mindset deeply rooted in sexism where men are seen as carriers for the family lineage and more likely to obtain higher status in society.

However, there is a cost to male-ism for the expectant mother. Every day, approximately one pregnant mother dies every two minutes due to preventable complications related to pregnancy and childbirth. And one of the major reasons why mothers face problems during labor is because of an obstruction in the birth canal where the baby’s head (which is supposed to exit first) is too large for the opening. According to a study done with a Nepalese population, mothers delivering male babies had an 18% higher chance of experiencing obstructed labor, as males are more likely to be larger babies.

And it’s not just a problem in humans. Mothers of mammals like cattle, water buffalo, sheep, and goats are also likely to suffer from “dystocia,” or prolonged and challenging labor. But the difference between most animals and humans is that humans have a narrower pelvis, suited for walking, but less so for childbirth.

So why do males exist if they struggle through the birth canal? Natural selection and self preservation. In order for humanity to continue, we must continue to reproduce. Just like how a runt in a litter of puppies is more likely to be the first to die, natural selection has favored larger offspring because they are more likely to thrive post-birth.

This isn’t to say there aren’t trade-offs. A balance must be met, because too large of a male baby endangers the birthing mom, and females are the only biological sex capable of reproducing.

When a woman becomes pregnant, there is a 50-50 chance that the baby will be a boy or girl. The even odds of the sex push some couples to wait until the baby is born to find out the gender, but Professor Amanda Sferruzzi-Perri, a Fellow of St John's College says that “actually knowing the sex would help to identify whether a pregnancy may be at greater risk than another.” Sferruzzi-Perri and her team found that fetal sex affects how well the placenta functions, and that male fetuses may be more vulnerable to complications because of their higher nutrient demands. Maternal obesity and diabetes pose a risk for both mother and child if the fetus cannot pass through the birthing canal.

Thus, knowing the sex of a baby could enable providers to develop a sex-specific pregnancy plan that promotes adequate nutrition for the growing fetus while still maintaining a healthy maternal weight.

So while it may be cute to save the baby’s gender as a surprise until their birth, the growing body of evidence suggests that it can be worthwhile to have an early celebration and find out the sex sooner. Doing so could meaningfully inform prenatal care, and help ensure a safer pregnancy for both mother and child.