At one time, 37 weeks was considered full term for babies in the womb. That meant doctors felt that they were developed enough to be delivered safely.

But doctors started to realize something after too many inductions resulted in complications. It turns out that 37 weeks isn’t the best age for babies to pop out. There are reasons a woman’s body keeps that baby in there longer.

Too many babies were born with complications at 37 weeks. As a result, the American College of Obstetricians and Gynecologists changed its official guidelines.

Any pregnancy over 39 weeks is now considered full term. Babies born 37 weeks to 38 weeks and six days are considered early term.

The new guidelines have resulted in more babies staying in the womb longer. But it can be hard to shake the old way of thinking about 37 weeks being OK. And if that’s the case, a 36-week baby should be fine too, right?

In most cases, the answer is yes. But there are a few things you should know.

It turns out that whatever due date your doctor gave you might be off by a week. So if you consider yourself full term at 37 weeks, you may only be 36 weeks pregnant.

Unless you conceived through in vitro fertilization (IVF) and have scientific proof of exactly when you became pregnant, your due date is likely off.

Even for women with regular, exactly 28-day cycles, the exact time of fertilization and implantation can vary. When you have sex, when you ovulate, and when implantation occurs all factor in.

For these reasons, it’s difficult to predict a precise due date. So whenever it’s not medically necessary to induce labor, it’s important to let it start on its own.

It’s best to let labor progress naturally. But sometimes babies are born prematurely. In cases involving conditions like preeclampsia, early delivery might even be the safest option. But there are still risks for babies born before full term.

At 36 weeks, a baby is considered late preterm. According to the journal Obstetrics and Gynecology, late preterm babies born between 34 and 36 weeks account for nearly three-fourths of all preterm births and about 8 percent of total births in the United States. The rate of babies born at this stage has risen 25 percent since 1990.

At 36 weeks, the risk of health complications decreases significantly. The risk is much lower from babies born even at 35 weeks. But late preterm babies are still at risk for:

As a result of complications, late preterm babies may need to be admitted to a neonatal intensive care unit (NICU) or even readmitted to the hospital after discharge.

RDS is by far the biggest risk for babies born at 36 weeks. Baby boys seem to have more trouble than late preterm girls. Although only about 5 percent of babies born at 36 weeks are admitted to the NICU, almost 30 percent experience some degree of respiratory distress.

Infant mortality for babies at 36 weeks, after accounting for babies with undetected heart abnormalities, was around 0.8 percent.

In most cases, delivery at 36 weeks isn’t by choice. Most babies born late preterm happen because of premature labor or a woman’s water breaking early. In those situations, it’s best to know what risks your newborn could face and prepare a plan with your doctor.

If you’re considering voluntary early induction, the moral of the story is to keep that baby in there as long as possible.