Giving Birth Before Your Due Date: Do All 40 Weeks Matter?

Your due date is in sight, and you only have a few weeks to go. In fact, you're so close, you'd be happy to get the show on the road and have your baby now. What's the harm? Your doctor told you, after all, that at 37 weeks, you're close enough. It's safe to have your baby. But it turns out those last few weeks are just as important as any other phase of pregnancy, and "close enough" doesn't always cut it. A full term pregnancy, after all, is one which lasts at least 39 weeks.

"The evidence is so compelling that a growing number of American hospitals are launching programs to help prevent elective deliveries before 39 weeks of gestation," says Diane Ashton, M.D., deputy medical director of the March of Dimes. Research now suggests that birthing a baby prior to 39 weeks puts them at risk for a range of health and developmental problems.

But what happens, really? Here's everything you need to know about term pregnancies, from what they are to why those last few weeks of pregnancy matter.

What is Full Term Pregnancy?

While most people believe a "full term" pregnancy is one which lasts 37 weeks, that is not the case. According to the American College of Obstetricians and Gynecologists and the Society for Maternal-Fetal Medicine, a full-term pregnancy is one which lasts between 39 weeks, 0 days and 40 weeks 6 days. This means you give birth 1 week before your due date and/or up to 1 week after. Babies born during week 37 and 38 are considered early term, and those born after 41 weeks are late term—or postterm, depending on when baby makes their appearance.

Of course, this has not always been the case. Just a few years ago, pregnancies used to be considered at term, and babies ready for delivery, any time week 37. (Most physicians believed that major organ development was complete at this time and that babies simply packed on pounds during the last stretch of pregnancy.) However, after a couple of decades that have seen too many C-sections and record numbers of babies in the neonatal intensive care unit (NICU), those last few weeks of pregnancy are being taken seriously.

"We now know that important organs, such as the lungs and the brain, are not fully developed until 39 weeks," says Jason K. Baxter, M.D., an Ob-Gyn who specializes in high-risk pregnancies at Thomas Jefferson University Hospital, in Philadelphia.

Why the Change, i.e. How Was the Length of Pregnancy Defined In the Past?

Doctors and hospitals have learned so much from the mistakes made back in the day, when inductions and C-sections were as easy to schedule as a haircut and were often done by (and with) parents who were only 37 and 38 weeks pregnant. Many of these procedures were done not out of medical necessity but for convenience sake. To make sure grandma could be at the birth, for example, or so the birthing parent could be sure their own doctor would be on-call.

But because due dates are often miscalculated, especially by ultrasound, doctors were frequently delivering premature babies who wound up spending time in the NICU. One study, for example, found that babies born by C-section before 39 weeks have more breathing difficulties than babies delivered by C-section after 39 weeks. Furthermore, babies delivered electively at 37 weeks are four times more likely to end up in the neonatal intensive care unit or have serious respiratory troubles than babies born at 39 weeks or later; babies who arrive at 38 weeks are twice as likely to have complications.

Additionally, many of the inductions were unsuccessful because mom's body was not ready to go into labor. These individuals wound up with C-sections they most likely wouldn't have needed if they'd waited for labor to start on its own.

Why Do Those Last Few Weeks Matter—and Is It Safe to Give Birth at 37 Weeks?

You may be tempted to ask your doctor for an early induction because of swollen ankles or an aching back, but that final month is critical to your baby's good health. For starters, a compound in their lungs called surfactant, which enables them to breathe independently, continues to be produced in greater amounts during the last month of pregnancy and decreases baby's risk of developing breathing problems once they arrive. Their liver is still undergoing changes, too—ones that will enable it to properly filter toxins, such as jaundice-causing bilirubin, out of her body.

Of course, that's not all. Baby's skin continues to thicken during the last few weeks of pregnancy, and they are accumulating more body fat, which will help them maintain their own body temperature after they're born. Brain development is still underway; at 35 weeks, for example, its volume is only about two thirds of what you'd expect at 39 to 40 weeks, says Dr. Ashton. Additionally, important brain and nerve connections are being made to help baby suck, swallow, breathe, and even sleep better once they're born.

That said, it's important to note that if you do go into labor early, you shouldn't fret. Doctors and hospital staff are well-equipped to care for you and baby, should the need arise. So while you should aim to carry baby as long as possible, many facilities can (and do) care for babies born at or before 37 weeks.

The Bottom Line

Slowly but surely the birth culture of "induction or C-section on demand" has changed. Now, most doctors have received the memo that unnecessary inductions are potentially dangerous, for both the expectant parent and their baby/babies. If there are solid, compelling medical reasons to induce or schedule a C-section, then, by all means, that's what those procedures are there for. However, if the medical reason can wait until a baby is full term, everyone fares better.