Concerns About Preterm Birth Extend to the Last Few Weeks

When I was training in pediatrics, back in the 1980s, we spent a lot of time working in the newborn intensive care unit, where relatively new — and rapidly evolving — technologies made it possible to save extremely premature infants. A full-term pregnancy lasts for 40 weeks, and we were often taking care of babies born at 27 or 28 weeks, and sometimes earlier, impossibly tiny infants who were clearly not ready to exist outside the womb.

We worried less about the bigger, more clearly mature babies who were just a month or a little more early; the chief question was whether they weighed enough to go home — otherwise they had to stay in the hospital to “feed and grow.” And there was a general sense that that was also what those last weeks in the womb were mostly about.

But the thinking has shifted as new research has shown that every week that a baby stays in the womb makes a difference in health and development, even those last few.

“They’re not done yet, they’re just not done yet,” said Dr. Wanda Barfield, the director of the division of reproductive health at the Centers for Disease Control and Prevention. In that excitement over being able to save the profoundly premature infants, medicine lost sight for a while of the fact that the infants born at 34 and 35 and 36 and 37 weeks gestation “weren’t just little term babies, weren’t mature, had a lot of needs to continue their physiological maturity,” she said.

This led, in some cases, to a rather cavalier attitude toward delivering babies early, even when not medically indicated. But when researchers looked more closely at these “late preterm” infants, they found that they were at increased risk of a whole range of medical problems and developmental issues.

One important result of the research on late preterm infants was that the American College of Obstetricians and Gynecologists recommended strongly against early deliveries, unless they were medically necessary. Between 2007 and 2014, Dr. Barfield said, late preterm births declined, but since 2014, there has been an uptick. “We’re losing ground,” Dr. Barfield said. And there are also concerning disparities with higher rates of prematurity among African-American and Hispanic women.

Dr. Prachi Shah, an associate professor of pediatrics at C.S. Mott Children’s Hospital at the University of Michigan, said, “when we think about the morbidities of preterm birth, most studies have focused on the very preterm infant, less than 32 weeks, less than 28 weeks.” However, she said, from a public health point of view, late preterm births — from 34 to 37 weeks — account for the majority of preterm births — about 70 percent — and for 7 percent of all live births.

The terminology was revised in a 2007 report by the American Academy of Pediatrics: Babies born from 34 to 36 6/7 weeks gestation were classified as “late preterm,” rather than “near term.” Those born from 37 to 38 6/7 weeks are now called “early term” babies, and only those who stay inside for 39 to 40 6/7 weeks are considered full term. Early term infants represent another 26 percent of all live births.

In pediatrics, late preterm infants are now considered an at-risk population. Most immediately, they are at higher risk of medical problems in the newborn period, including poor feeding, dehydration, jaundice and hyperbilirubinemia. They may have trouble maintaining their blood sugar levels, and they may have trouble maintaining their temperatures. They are more likely to be readmitted after they go home from the hospital.

When researchers control for underlying conditions associated with early deliveries, like maternal hypertension or diabetes, late preterm infants are still at higher risk than full-term infants whose mothers have those same problems.

As they grow, the late preterm children are also at increased risk for developmental problems, Dr. Shah said. “Beyond the perinatal period, at a population level, when compared to full-term infants, there is a higher incidence of learning difficulties and minor cognitive and neurologic issues.”

In a recent study, researchers looked at data from a group of almost 6,000 children in New York (the Upstate KIDS cohort, born outside New York City from 2008 to 2010) who were regularly assessed during the first three years of life through parental questionnaires. The researchers also looked to see whether children had been found eligible for early intervention services, which are provided to those with developmental delays.

Edwina Yeung, a senior investigator at the Eunice Kennedy Shriver National Institute of Child Health and Development division of intramural population health research, who was the senior author, said, “We were trying to look at this in a longitudinal way, as a continuum of gestational age.”

Although the most marked risks were found in children born at the lower gestational ages (32 weeks and below), the relationship was consistent: The longer babies stayed in the womb, the less likely they were to show developmental delays on the questionnaires, and to qualify for early intervention services. The late preterm infants were at higher risk than the early term infants, but those born at 37 and 38 weeks gestation were also at higher developmental risk, with a greater likelihood of failing the gross motor and communication domains of the questionnaire. Even 39 weeks was not as good as 40 or 41.

“Nobody doubts that preterm delivery is a problem,” Dr. Yeung said. “The question of interest is in that small window around 40 weeks with term deliveries and early term deliveries.”

Dr. Shah, who was not involved with this study, said, “The key take-home message is that every week seems to make a difference in terms of developmental delay — the earlier you were born, the higher your risk for developmental delay.”

Dr. Shah was the first author of a 2016 study which found that at preschool and kindergarten entry, children born in the late preterm period had lower math and reading scores than children born at term. “Compared to full-term infants, there is an increased risk of developmental vulnerability, but the magnitude of effect is not as great as those born very preterm,” she said.

Still, these are children who should be identified — and helped — before they get to school. “We have missed a window to intervene,” Dr. Shah said. “If we have evidence that there are population-based differences, we should be thinking about them as a vulnerable population that may need targeted surveillance.” It may be important to look closely at which late preterm infants should be monitored most closely, she said, and to consider extending the eligibility for services like early intervention.

In terms of development, Dr. Shah said, many of the risks for late preterm and early term infants seem to be around communication and language delays, and around math. “Every week of intrauterine life makes a difference in these neurodevelopmental processes,” Dr. Shah said. “Even a week early can seem to result in structural changes.”

Dr. Barfield was the co-author of a 2019 update on the late preterm infant from the American Academy of Pediatrics, which emphasizes the importance of strategies for preventing prematurity. The A.A.P. recommends against early discharge for these newborns, and suggests that they come back for follow-up visits after discharge.

They need to be breastfeeding well, and able to maintain their body temperatures. Their families need to be clear on the rules of safe sleep and fully informed about all the other warning signs to watch for, from jaundice to lethargy to breathing problems.

“We need to understand that these babies are premature,” Dr. Barfield said. “Although they may be closer in terms of time, they are still premature infants.”


Tags: health

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