Table 3. Stratified analyses estimating associations between microcephaly and maternal and newborn co-factors in each cohort.

Univariate analyses assessing the relationship between maternal and newborn factors and microcephaly in each cohort are shown. For each cohort the frequency of cases is shown, and χ ² test used for all analyses. When all variables that were statistically significant at p<0.05 in any of the cohorts (indicated by *) were included in a multivariable logistic regression model, only SGA maintained an association with microcephaly (adjusted OR=3.41, 95% CI 2.30, 5.06, p<0.001).

	LMP cohort			Scanned cohort
Covariate	Categories	n/N cases (%)	P value	n/N cases (%)	P value
A) Newborn factors
Sex	Male	58/4047 (1.4%)	0.10	11/747 (1.5%)	0.18
	Female	37/3618 (1.0%)		5/685 (0.7%)
Small for gestational age (SGA) *	Normal	51/6184 (0.8%)	<0.001	10/1147 (0.9%)	0.08
	SGA	44/1481 (3.0%)		6/285 (2.1%)
Type of birth *	Singleton	92/7472 (1.2%)	0.69	14/1393 (1.0%)	0.001
	Multifetal	3/193 (1.5%)		2/25 (8.0%)
Year of birth	2012	17/1312 (1.3%)	0.05	0/69 (0)	0.75
	2013	25/1225 (2.0%)		3/274 (1.1%)
	2014	14/1712 (0.8%)		9/667 (1.3%)
	2015	19/1621 (1.2%)		4/422 (0.9%)
	2016	20/1795 (1.1%)		No data
&Season	January - March	21/1835 (1.1%)	0.33	3/410 (0.7%)	0.18
	April - June	34/2379 (1.4%)		7/363 (1.9%)
	July - September	17/1899 (0.9%)		5/341 (1.5%)
	October - December	23/1552 (1.5%)		1/318 (0.3%)
B) Maternal factors
Sociodemographic factors
Maternal age	<20 years	14/1164 (1.2%)	0.49	3/175 (1.7%)	0.59
	20 to 35 years	76/5835 (1.3%)		11/1131 (1.0%)
	>35 years	5/659 (0.7%)		2/124 (1.6%)
Marital status *	Married	87/6999 (1.2%)	0.68	12/1330 (0.9%)	0.002
	Unmarried	6/575 (1.2%)		4/90 (4.4%)
Education level	Secondary or more	20/2221 (0.9%)	0.22	1/406 (0.2%)	0.15
	Primary school	62/4443 (1.4%)		11/810 (1.4%)
	None	10/832 (1.2%)		3/178 (1.7%)
Residence	Other	60/5293 (1.1%)	0.19	10/600 (1.7%)	0.09
	Kilifi township	35/2346 (1.5%)		6/830 (0.7%)
Type of house *	Stone wall	36/3902 (0.9%)	0.02	9/800 (1.1%)	0.99
	Mud wall	56/3708 (1.5%)		7/620 (1.1%)
Obstetric history
Parity	Primigravida	39/2814 (1.4%)	0.40	2/488 (0.4%)	0.06
	Multigravida	56/4812 (1.2%)		14/926 (1.5%)
Antenatal care
Antenatal care attendance	≥4 visits	57/4501 (1.3%)	0.87	12/1221 (1.0%)	0.22
	0 to 3 visits	38/3102 (1.2%)		4/203 (2.0%)
Medication during pregnancy
Folic acid supplements	Yes	86/6947 (1.2%)	0.95	16/1345 (1.2%)	0.32
	No	9/713 (1.3%)		0/82 (0)
Malaria prophylaxis	≥3 doses	53/4106 (1.3%)	0.07	8/1060 (0.7%)	0.05
	1 to 2 doses	40/2785 (1.4%)		7/285 (2.5%)
	None	2/632 (0.3%)		1/57 (1.7%)
Tetanus vaccination	Yes	79/6456 (1.2%)	0.82	16/1250 (1.3%)	0.17
	No	13/994 (1.3%)		0/143 (0)
Maternal co-morbidities and infections
Mid-upper arm circumference (MUAC)	Normal (23-30cm)	65/5417 (1.2%)	0.85	11/1073 (1.0%)	0.22
	Low (<23cm)	9/822 (1.1%)		4/168 (2.4%)
	High (≥30cm)	8/812 (1.0%)		1/185 (0.5%)
Hypertension in pregnancy	No	77/6296 (1.2%)	0.31	15/1327 (1.1%)	0.996
	Yes	8/452 (1.8%)		1/88 (1.1%)
HIV status	Negative	91/7277 (1.1%)	0.78	16/1328 (1.2%)	0.30
	Positive	4/278 (1.4%)		0/87 (0)
Maternal anaemia	No	19/1885 (1.0%)	0.46	2/436 (0.5%)	0.21
	Yes	56/4570 (1.2%)		10/866 (1.1%)
VDRL (syphilis test)	Negative	79/6732 (1.2%)	0.34	16/1282 (1.2%)	0.71
	Positive	1/34 (2.9%)		0/11 (0)
Other risk exposures
Substance use	No	93/7459 (1.2%)	0.75	15/1396 (1.1%)	0.26
	Yes	2/201 (1.0%)		1/31 (3.2%)
Contact with cattle	No	87/6907 (1.3%)	0.99	14/1318 (1.1%)	0.13
	Yes	5/399 (1.2%)		2/64 (3.1%)