Determining Gestational Age
The duration of a pregnancy is measured by gestational age (or the amount of time elapsed since the first day of the last menstrual period). A normal gestation lasts 40 weeks or 279 days. If delivery occurs before 37 weeks gestation, the baby is considered prematurely born.
Some elements that can make it difficult to calculate your child’s gestational age are irregular menstrual periods or first trimester vaginal bleeding. To improve the accuracy of gestational age estimates, some doctors use an ultrasound examination before 20 weeks gestation to confirm or correct the gestational age estimate.
Understanding Birth Weight
Birth weight can also indicate whether a baby is born prematurely. Babies born with a weight of less than 2,500 grams (about five and one-half pounds) are considered to have low birth weight. Generally, infants with a birth weight less than 2,500 grams are premature. However, babies can be premature but weigh more than 2,500 grams at birth. They can also be born at term and weigh less than 2,500 grams. There is no perfect system for categorizing infants, and so measurements, birth weight, and gestational age, are all used.
Prevalence of Premature Delivery
About 11 percent of all babies are born before 37 weeks gestation. Many premature deliveries occur close to term, and these infants generally do well. Infants born more prematurely than 32 weeks gestation routinely require long hospital stays and may also need attention in a special care nursery.
The risk of complications accelerates as gestational age decreases. Children born 16 weeks prematurely have many more complications than those born eight weeks prematurely.
According the CDC, the preterm birth rate rose two percent in 2004 to 12.5 percent of all births. Over one-half million babies were born preterm in 2004, the highest number reported since gestational age has been available from birth certificates (which began in 1981).
|Incidence of Prematurity|
Gestational Age (Weeks)
Percent of all births
Data from the National Vital Statistics Report (vol. 55, no. 1), published September 29, 2006, by the CDC.
Common Risk Factors
Some women are at much higher risk of prematurely delivering an infant than others. Here are some of the common risk factors:
- Maternal age (younger than 18 or older than 35 years)
- Previous premature delivery
- Vaginal infection
- Uterine malformations (septum, etc.)
- Elevated blood pressure during pregnancy
- Multiple gestation, such as twins or triplets
- African-American race
If you have any of these factors, you should discuss your risk of premature delivery with your doctor.
How to Reduce Your Risks
The transition from inside to outside the womb causes the problems of prematurity. After birth, babies are no longer able to depend on their mothers for biological support. Lungs, heart, brain, liver, and intestinal tract are all forced to operate independently of the mother’s nurturing uterine environment. Depending on how prematurely the baby is born, these organs may not be prepared to assume their functions.
Taking Your Preemie Home
Each hospital has slightly different criteria for discharging prematurely born babies. The infants themselves also vary in the time they require to mature. In general, babies must be able to do the following things before they go home:
- Maintain body temperature outside of the incubator. Until babies are about 1,700 grams in weight (three pounds, 12 ounces) they usually do not have sufficient body mass and subcutaneous fat to maintain their body temperatures.
- Breathe on their own. Prematurely born babies sometimes forget to breathe; this is called apnea. It is very common among premature babies and usually improves rapidly as the baby approaches 40 weeks of age (total gestational age plus weeks since birth). Even if apnea is still a problem when the baby is otherwise ready for discharge, he may still be sent home with an apnea monitor.
- Eat on their own. Prematurely born infants may not have coordinated suck and swallow reflexes at birth and for several weeks thereafter. They are frequently fed by tube in the hospital. Before discharge, almost all hospitals require that the infant be able to take all feedings either by breast or bottle.
New Promise for Premature Infants
Premature delivery is one of the most important causes of serious illness among newborn infants. Recent reductions in infant mortality rates have occurred primarily through more effective treatment of prematurely born infants.
Even for the most premature infants, the outlook is improving. In fact, in February 2006, the youngest ever premature infant went home after a four-month stay in the Miami Baptist Children’s Hospital neonatal care unit. Amillia Sonja Taylor, born October 24, 2006, was just nine and one-half inches long and less than 10 ounces at her birth. She was born after an amazingly short 21 weeks, six days in the womb.
“It may be that we need to reconsider our standard for viability in light of Amillia’s case,” reports Dr. William Smalling, MD, neonatologist at Baptist Children’s Hospital. “Over the years, the technology that we have available to save these premature babies has improved dramatically. Today, we can save babies that would have never survived 10
years ago,” he adds.
Additionally, a new study done at the University of Florida and published in the January 2006 issue of Pediatrics found that extremely premature baby girls were 1.7 times more likely to survive than baby boys. And African-American baby girls were 2.1 times as likely to survive as white boys.
This new study also reports some promising statistics on survival rates for premature babies.
|Premature Babies’ Survival Rates*|
Gestational Age (Weeks)
“Racial and Gender Differences in the Viability of Extremely Low Birth Weight Infants: A Population-Based Study,” Pediatrics, Jan. 2006, volume 117, number 1.
Premature delivery is a common contributor to infant mortality and a reason for admission to the NICU. Fortunately, even for very premature children, the outcome is often positive and continues to improve. The best treatment of prematurity is prevention. You can reduce your risk of premature delivery by keeping all prenatal appointments, avoiding tobacco and recreational drugs, and promptly reporting any danger signs that might indicate premature labor or other complications.