Maternal characteristics and factors associated with risk of mild microcephaly
| Characteristic | Mild microcephaly | Normocephaly | Prevalence rate per 100 | OR 95% CI | |
| Unadjusted | Adjusted* | ||||
| Maternal age (years) | |||||
| <25 | 312 | 4932 | 6.0 | 1.37 (1.19 to 1.58) | 1.29 (1.06 to 1.42) |
| 25–29 | 988 | 17 275 | 5.4 | 1.24 (1.12 to 1.38) | 1.13 (1.01 to 1.25) |
| 30–34 | 605 | 13 125 | 4.4 | 1.00 (reference) | 1.00 (reference) |
| ≥35 | 197 | 6702 | 2.9 | 0.64 (0.54 to 0.75) | 0.54 (0.41 to 0.72) |
| Education | |||||
| University/college | 1311 | 25 464 | 4.9 | 1.00 (reference) | 1.00 (reference) |
| High school | 312 | 6 64 | 4.7 | 0.97 (0.85 to 1.10) | 0.99 (0.87 to 1.13) |
| Elementary school | 479 | 10 306 | 4.6 | 0.90 (0.81 to 1.01) | 1.02 (0.91 to 1.14) |
| Primiparity | 1850 | 34 052 | 5.2 | 1.72 (1.51 to 1.97) | 1.73 (1.50 to 2.01) |
| Cantonese ethnicity | 1888 | 35 703 | 5.0 | 1.56 (1.36 to 1.81) | 1.45 (1.25 to 1.68) |
| IVF conception | 89 | 2 487 | 3.5 | 0.72 (0.57 to 0.89) | 0.78 (0.65 to 0.96) |
| Congenital heart disease | 22 | 423 | 4.9 | 1.04 (0.68 to 1.60) | 0.89 (0.57 to 1.38) |
| Other congenital anomalies in offspring† | 25 | 415 | 5.7 | 1.21 (0.80 to 1.81) | 1.23 (0.81 to 1.86) |
| Intrauterine growth restriction | 40 | 172 | 18.8 | 4.72 (2.34 to 6.68) | 4.48 (3.14 to 6.40) |
| Maternal anomalies | 15 | 375 | 3.9 | 0.80 (0.48 to 1.34) | 0.80 (0.48 to 1.35) |
| Diabetes mellitus | 216 | 5095 | 4.1 | 0.83 (0.72 to 0.96) | 0.96 (0.83 to 1.11) |
| Pre-eclampsia | 44 | 819 | 5.1 | 1.08 (0.79 to 1.46) | 1.10 (0.81 to 1.51) |
| Chronic illness | 276 | 6027 | 4.4 | 0.90 (0.79 to 1.03) | 0.92 (0.81 to 1.05) |
| Teratogens | 35 | 591 | 5.6 | 1.18 (0.84 to 1.67) | 1.22 (0.86 to 1.73) |
| TORCH agents‡ | 11 | 313 | 3.4 | 0.70 (0.38 to 1.28) | 0.70 (0.38 to 1.28) |
| Genital/reproductive infections | 19 | 669 | 2.8 | 0.56 (0.36 to 0.89) | 0.66 (0.42 to 1.06) |
| Overall | 2102 | 42 034 | 4.8 | ||
*Adjusted for infant birth year.
†Exclusive of congenital heart disease and CNS anomalies.
‡Latent T oxoplasma gondii only.
CNS, central nervous system; IVF, in vitro fertilisation; TORCH, Toxoplasma gondii, rubella virus, cytomegalovirus, herpes simplex virus.