Table 1. Relationship between confounders and maternal Vitamin D status.

Confounder	Maternal vitamin D status
	< 50.0 nmol/L			≥ 50.0 nmol/L
	Mean	SD	n	Mean	SD	n	p value†
Age of mother (yrs)	27.7	4.8	2443	28.6	4.7	4622	< 0·0001
BMI of mother (Kg/m2)	23.0	4.0	2126	22.9	3.6	4095	0.43
Gestation of vitamin D measure (weeks)	23.4	10.9	2771	25.7	10.3	5174	< 0·0001
	%	n		%	n		p value ‡
Breastfeeding
Some	33·0%	1738		67·0%	3526		< 0·0001
None	38·8%	553		61·2%	874
Crowding in the home
< one person per room	33·9%	2140		66·1%	4170		< 0·0001
One or more per room	43.6%	176		56·4%	228
Education of mother
Low	37·5%	716		62·5%	1195		< 0·0001
Medium	33·4%	792		66·6%	1577
High	31·5%	755		68·5%	1643
Ethnicity of mother
White	33·3%	2171		66·7%	4344		< 0·0001
Non–white	60·6%	83		39·4%	54
Gender of child
Male	34·3%	1266		65·7%	2421		0·67
Female	34·8%	1177		65·2%	2201
Housing status
Owned/mortgaged	32·8%	1705		67·2%	3487		< 0·0001
Other rented	36·6%	150		63·4%	260
Council rented	41·0%	491		59·0%	708
Iodine–to–creatinine ratio in 1st trimester
<150 μg/g (deficient)	33.5%	186		66.5%	374		0.94
≥150 μg/g (sufficient)	33.2%	76		66.8%	151
Oily fish intake in pregnancy (/week)
Never/rarely	37·7%	1038		62·3%	1718		< 0·0001
Once per fortnight or more	31·3%	1191		68·7%	2617
Parity
Zero	37·0%	1125		63·0%	1914		< 0·0001
One or more	31·9%	1179		68·1%	2516
Season of vitamin D measure
Spring	48.8%	980		51.2%	1027		< 0·0001
Summer	15.2%	268		84.8%	1491
Autumn	22.4%	363		77.6%	1257
Winter	49.5%	831		50.5%	847
Smoking in 1st trimester
No tobacco	31·7%	1652		68·3%	3567		< 0·0001
Smoked tobacco	42·5%	689		57·5%	932
Social class of mother
Manual	36·6%	383		63·4%	664		0·01
Non–manual	32·5%	1447		67·5%	3008

^†p value from independent t-test.

^‡p value for χ2 test.