Table 3.

Population attributable fractions and 95% confidence interval associated with identified factors for microcephaly and its subtypes

Risk factors	Microcephaly	Disproportionate microcephaly	Proportionate microcephaly
All risk factors combined	66.4% (43.9–81.1%)	47.5% (13.1–71.7%)	67.7% (47.7–81.1%)
Specific factors
Primiparity	28.9% (10.3–45.5%)	–	28.2% (7.9–46.3%)
HDP	–	–	1.9% (− 3.2 to 6.9%)
Maternal carrier of HBV	4.8% (−1.2 to 10.8%)	–	–
Small for gestational age	50.6% (38.8–60.8%)	–	56.5% (44.0–66.9%)
Preterm birth	4.0% (− 1.4 to 9.4%)	47.5% (13.1–71.7%)	–

HDP Hypertensive disorders of pregnancy, HBV Hepatitis B Virus