The preterm birth rate has increased markedly in recent decades, mainly because of the increase in late preterm (LP) births. Late preterm infants are those born between 34+0 and 36+6 weeks’ gestation and account for more than 70% of all prematurely born infants in the United States. Moderately preterm (MP) (32+0–33+6 weeks) and LP infants together comprise more than 80% of all preterm births. Late preterm infants may have poor neurodevelopmental outcomes, and one relatively common disorder is cerebral palsy (CP), diagnosed based on medical history, imaging data, and clinical multidisciplinary evaluations. Cerebral palsy incidence also depends on gestational age (GA) in very preterm (VP) infants. Risk factors for CP have been identified for term infants, but not as thoroughly for MP and LP infants. This Finnish national-register study was performed to compare the CP incidence among LP and MP infants to that in VP and term infants and to identify risk factors for CP.
The study population included all 1,039,263 infants born in Finland from 1991 to 2008. Data on baseline and pregnancy/infant characteristics, live births, deaths, and congenital anomalies were collected from several national registries. After exclusions, the final cohort included 1,018,302 infants. Infants were followed up to age 7 years or to 2009. Gestational age categories were classified as VP (≤32+0 weeks, n = 6347), MP (32+0–33+6 weeks, n = 6799), LP (34+0–36+6 weeks, n = 39,932), and term (≥37 weeks, n = 965,224). Time periods were 1991 to 1995, 1996 to 2001, and 2002 to 2008. Pregnancy-related risk factors were the number of fetuses and their order, timing of birth, in vitro fertilization, and cervical cerclage. Resuscitation at birth included intubation, mechanical ventilation, or chest compressions.
Late preterm and MP infants accounted for 75% and 13%, respectively, of all premature infants born during the study period. The proportion of all preterm births was 5.02% in 1991 to 1995, 5.43% in 1996 to 2001, and 5.18% in 2002 to 2008. Moderately preterm infants accounted for 0.63% to 0.69% and LP infants for 3.82% to 4.08% of all births. Cerebral palsy was diagnosed in 2242 cases. The incidence of CP was 0.22%, and this rate decreased nonlinearly with increasing GA and time. The proportion of diplegia cases was greatest in the VP group and of hemiplegia cases in the term group. Birth during 1991 to 1995, 1-minute Apgar score of less than 7, and intracranial hemorrhage predicted CP in all GA categories in the logistic regression model. Resuscitation at birth was associated with an increased risk in the MP, LP, and term groups. Small for GA and antibiotic treatment during the first hospitalization seemed to predict an increased risk of CP in the LP and the term groups. Premature rupture of membranes was associated with an increased risk and antenatal steroid treatment with a decreased risk of CP in the MP group. In the analysis for 2004 to 2008, the odds ratio for CP in the MP group with antenatal steroids was 0.24 (95% confidence interval [CI], 0.08–0.76). Respiratory distress syndrome predicted a decreased risk of CP in the LP group. Independent odds ratios for CP in premature groups compared with the full-term group were 9.37 in the VP group (95% CI, 7.34–11.96), 5.12 in the MP group (95% CI, 4.13–6.34), and 2.35 in the LP group (95% CI, 1.99–2.77).
The incidence and risk for CP were higher in MP and LP infants compared with term infants. The medical expense burden of CP to the families of the MP and LP children was comparable to term-born babies. The need for disability allowance was significantly less common in the MP and LP groups than in the VP cases. These results could be used to counsel parents and to plan for follow-up with of MP and LP newborns. Future studies should create and evaluate guidelines for management, and risk assessment should be established for LP and MP infants.