Preterm boys cognitively catch up to their peers by age 7, while girls lag behind

Image: CC/Courtesy of PLOS

Key study points

1.  Children born moderately premature, at 32 to ~37 weeks, have lower intelligence, verbal memory, and visuomotor skills than full-term children.

2.  By age 7, moderately premature boys are more likely to have caught up to their full-term peers than girls, lagging behind only in visuomotor skills, while girls lag behind in multiple neuropsychological domains.

Primer: Since 1990 there has been an 21% overall rise in the proportion of infants born preterm and an increase in the survival rate of preterm infants.  However, this increase in preterm survivors has not been matched by a decrease in neurodevelopmental sequelae.  While moderately preterm infants are appear to be physically developed at birth and often attain the same size and weight as full term infants, long-term neurodevelopmental outcomes do not match their peers by preschool age.  Studies in North America and Western Europe have shown increased prevalence of impairment in cognitive skills, motor deficits, and sensory impairment among preterm infants compared to infants born at full term.  This study compared neuropsychological and motor functioning at age 7 between moderately preterm children and children born full-term, with special attention to differences by gender.

Background reading:

1.  Functioning at school age of moderately preterm children born at 32 to 36 weeks’ gestational age.  [Pediatrics]

2.  Cognitive and Behavioral Outcomes of School-Aged Children Who Were Born Preterm: A Meta-analysis  [JAMA]

This [prospective cohort] study included 248 moderately preterm children (32 weeks to 35 weeks and 6 days) and 130 full-term children (38 weeks to 41 weeks and six days) born from 2002 to 2003 in the Netherlands.  Exclusion criteria were congenital malformation, congenital infection, or syndromes. Neurological testing included IQ estimation, verbal memory, visuospatial reasoning, visuomotor functioning, attention control, and executive functioning.  Mean scores revealed that moderately preterm children performed more poorly than the full-term population.  Preterm boys performed significantly worse only on visuospatial reasoning, while preterm girls performed significantly worse on visuospatial reasoning, intelligence, attention, and executive function.  No differences from the full-term population were seen in either gender for verbal IQ, verbal memory, motor, and visuomotor function.

In sum: Preterm birth is associated with early neuropsychological delays, even for the moderately pre-term population, including in visuospatial reasoning, intelligence, attention, and executive function.  The data suggest that boys are more likely to have largely caught up to their peers than girls by age 7; in particular, the only domain in which they lag behind is visuospatial reasoning. This was the domain with which preterm children showed the most difficulty as a group; many preterm children display nonverbal learning disabilities, for which visuospatial reasoning is known to be a marker. The reasons behind and implications of the gender differences for therapeutic interventions need to be established. The relevance of these results for children born in other countries, who are receiving different social services and of different demographic backgrounds, remains unclear.

Click to read the study in [Pediatrics]

By [SS] and [DB]

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