Table 3.

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 Toxoplasma gondii only.

CNS, central nervous system; IVF, in vitro fertilisation; TORCH, Toxoplasma gondii, rubella virus, cytomegalovirus, herpes simplex virus.