Temporal trends in diagnoses of congenital microcephaly, Texas Hospital Discharge Diagnoses, 2000-2015.

OBJECTIVE: Assess temporal trends in congenital microcephaly.

METHODS: We used Texas inpatient discharge diagnoses between 2000 and 2015, restricting to newborns. Between 2000 and 2003, the maximum number of fields for recording diagnostic codes was eight, and between 2004 and 2015 it was 24. Microcephaly was classified into four subgroups based on co-occurring diagnoses: A (Known Causes), B (Other Birth Defects), C (Preterm Birth or Fetal Growth Restriction) and D (Isolated Cases).

RESULTS: We identified 2,301 cases of microcephaly or 4.0 cases per 10,000 live births. There was an increase in the prevalence of microcephaly in 2012-2015 compared with 2000-2003, odds ratio = 1.85 (95% CI 1.64-2.10) Significant temporal increases in microcephaly were observed within each of the four microcephaly subgroups and significant temporal increases were also observed for eight other neonatal diagnoses during the same time period. When we restricted our analysis to cases with microcephaly identified using only the eight diagnostic codes available throughout the entire study period, the temporal trend for microcephaly was diminished or absent.

CONCLUSIONS: It remains uncertain whether the observed increases in microcephaly and other neonatal diagnoses are real or an artifact of the change in the number of fields. However, since it is unlikely that there would be a simultaneous increase in microcephaly and eight other neonatal diagnoses, it is likely that some or all of the temporal increases in neonatal diagnoses are artifactual.