New definitions of full-term pregnancy and why they matter


New definitions of full-term pregnancy and why they matter

According to a new set of definitions endorsed by the American College of Obstetricians and Gynecologists, pregnancy is not full term until 39 weeks. 

This represents an important shift from the old understanding under which pregnancy was considered full-term by week 37. Currently, experts believe that you should do everything to make it to your due date and, ideally, deliver it naturally.

Why change the definitions?
This change became necessary because elective deliveries performed before 39 weeks without a medical reason consistently result in greater risks of health problems for Your Child. The risks include problems with breathing and issues of brain development. Because these risks are not widely understood, the rate of early delivery has risen as births are scheduled for reasons of healthcare provider’s convenience or old traditional beliefs. 

The new way of counting
For years, babies were considered full-term between 37 and 42 weeks of pregnancy. Many doctors believed that major organ development was complete by 37 weeks and that babies simply packed on extra weight during the last stretch of pregnancy. However, current research has proved them wrong. An obstetrician and gynecologist specializing in high-risk pregnancies, found that important organs, such as the lungs and the brain, are not fully developed until 39 weeks.

As a result of these findings, experts now don’t consider babies’ term until 39 weeks. Infants born during weeks 37 and 38 are considered early term. Babies born in week 41 are late-term and after week 42 and beyond are post-term. 

Be patient and don’t plan
The new definitions should encourage doctors to exercise more patience around the end of pregnancy and wait for spontaneous labor, which is the best way to determine the healthiest time for delivery. Unless there are some health conditions, labor should be allowed to start on its own.

Patience leads to fewer emergency surgeries
When women wait until week 39 or 40, it means there would be fewer labor via induction. The medications used to induce labor, such as oxytocin, might cause abnormal or excessive contractions, which can diminish your baby’s oxygen supply. And if induction does not work or leads to complications, surgery will often become necessary. A cesarean is especially problematic for the mother. It increases the risk of infection, heavy blood loss and can lead to vomiting and severe headache after the delivery. Cesarean delivery is three times riskier than natural birth.

Those last weeks matter
The final month is critical to Your Child’s health because a compound in the lungs called surfactant, which enables Your Child to breathe independently, continues to be produced in greater amounts during this period. This substance minimizes the risk of breathing problems when Your Child is born. For example, one study found that babies born by C-section before 39 weeks have more breathing difficulties than babies delivered by C-section after 39 weeks. In addition, 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 born at 38 weeks are twice as likely to have complications.

It’s also good for the brain and other organs
Your Child’s liver is still undergoing changes that will enable it to properly filter toxins, such as bilirubin which causes jaundice. The baby’s skin is thickening and accumulating more body fat, which helps to maintain body temperature after birth. Also, brain development is still underway; for example, at 35 weeks, its volume is only about two-thirds of what you’d expect at 39 to 40 weeks. Important brain and nerve connections are being made, which helps the baby to suck, swallow, and breathe when delivered.


Dr. Wanwadee Sapmee Panyakat (OB-GYN) (18 March 2019)


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