What Is Term Gestation? (From a Pediatrician's Point of View)

Your doctor or nurse practitioner may have told you that anytime after 37 weeks gestation is term — that the baby is mature and safe to be delivered. And, yes, most of the time, when a 37-week gestation baby is delivered, he is big enough to stay with Mom and his lungs are mature enough to breath room air. But truly, there is more to consider than size and lung maturity.

Reasons to Deliver at 37 Weeks Gestation:

Now, I don't pretend to be an obstetrician or perinatologist. I know about what happens to babies AFTER they are born. My perspective comes from dealing with the troubles that newborn babies get into AFTER they are born. The last few weeks of pregnancy can be physically stressful and dangerous for moms and babies. If your blood pressure is going up rapidly, if your blood sugar is getting out of control, if your ultrasounds are showing problems with the placenta or the amniotic fluid, or the baby's growth is compromised, then your doctors need to make the hard decision of what is healthier for both you and your baby — keep the baby inside or get him delivered. It's not an easy decision, and lots of factors have to be weighed and measured. Sometimes it is better to "get that baby out" so the medical problems of both Mom and baby can be managed independently.

Reasons to Wait until 40 Weeks Gestation:

However, three more weeks in mom's uterus makes a big difference in how fast a baby's body can adapt to being born. Within minutes, his lungs must adapt. Within hours, he must be able to clear mucous from the back of his throat, and he must be able to regulate his own blood sugar. Within 12 hours, his temperature control must adapt. Within 24 hours, his blood circulation must switch from inside-Mom's-uterus-not-breathing circulation to outside-with-all-the blood-going-through-the-lungs circulation. Within two days, his neurological system must respond to hunger so that he will awaken with enough frequency to eat and grow. Within three days, he must develop coordinated, efficient sucking and swallowing to take enough milk to grow. Also within three days, his liver must begin metabolizing bilirubin, the chemical that causes yellow jaundice.

From a pediatrician's point of view, those last three weeks — 38, 39 and 40 weeks — are really important. A full term baby is 40 weeks, not 37 weeks. Believe me when I tell you that 37-week gestation babies have more trouble with all of these adaptations then do 40-week babies. I deal with these things all the time in the newborn nursery. I sit with parents who expect to take their 37-week gestation baby home a day or two after birth, but the baby isn't ready.

I want every baby to go home when their parents go home, but being born early makes that difficult.

Common Problems for 37-Week Gestation Infants:

Weight

In the last three weeks of gestation, a healthy baby in a healthy mom can gain a pound a week. A seven pound term baby has a pound of fat to help get him through the first few days of life. While a five pound baby is big enough to not need an incubator, when he looses weight, and is down to four and a half pounds at three days old, he doesn't have any more weight to lose. If he isn't sucking well, or mom's milk hasn't come in yet, he's going to have to be fed some other way.

Temperature Control

The smaller the baby, the harder it is for him to keep his temperature in normal range. If he can't keep his temperature normal, he will need to go into an incubator and cannot stay with Mom.

Sleepiness

A newborn baby is pretty sleepy the first 24 hours after birth. He goes through a recovery period from the stress of birth and his neurological system needs time to recover. After 24 hours, we do expect him to waken more easily and to stay awake to suck eagerly for at least 20 minutes, six to ten times per 24 hours. But the nervous system in an early baby is less responsive. An early baby can be devilishly hard to waken and to keep awake. Since he is likely to be small, he must be fed. He may not waken to eat enough during a 24 hour period, and therefore does not gain weight.

Jaundice

After the baby is born, there is no more help from mom's metabolism and mom's placenta. The baby's body must adapt quickly to take care of all the metabolic functions. The chemical called bilirubin, which causes yellow jaundice, is metabolized by the liver. An early baby's liver needs more days to "switch on." 37- and 38-week gestation infants are much more likely to need treatment for yellow jaundice than 40-week infants.

Thanks to Janelle Aby MD, Stanford School Of Medicine, Newborn Nursery, and Lucille Packard Children's Hospital for the use of occasional photographs.