OBJECTIVE: To investigate whether maternal serum levels of 25-hydroxyvitamin D 
[25(OH)D] in the first trimester are altered in pregnant women with pre-existing 
type 2 diabetes, women who subsequently develop gestational diabetes mellitus 
(GDM) and women who deliver large for gestational age (LGA) neonates compared 
with normoglycaemic pregnant women who deliver an appropriate for gestational 
age (AGA) neonate.
DESIGN: Case-control study.
SETTING: Antenatal clinic.
POPULATION: Singleton pregnancies at 11(+0) -13(+6) weeks, including 50 women 
with type 2 diabetes, 100 women who subsequently developed GDM, 50 nondiabetic 
women who subsequently delivered LGA neonates and 1000 nondiabetic controls who 
delivered AGA neonates.
METHODS: Maternal serum total 25(OH)D levels were measured in the four groups of 
pregnancies. Multiple regression analysis in the controls was used to identify 
factors among maternal characteristics with a significant contribution to the 
levels of serum 25(OH)D, so that the values in all cases were expressed as a 
multiple of the median (MoM) in the controls.
MAIN OUTCOME MEASURES: Comparison of MoM 25(OH)D in the four groups.
RESULTS: In controls, significant independent contributions to the serum level 
of 25(OH)D were provided by maternal age, body mass index, smoking status, 
racial origin and season of sampling. The median and interquartile range (IQR) 
of serum 25(OH)D in the type 2 diabetes group (1.01; IQR, 0.68-1.47 MoM), GDM 
group (0.93; IQR, 0.67-1.23 MoM) and LGA group (0.97; IQR, 0.67-1.25 MoM) were 
not significantly different from those in the controls (0.99; IQR, 0.71-1.33 
MoM) (overall P = 0.643).
CONCLUSIONS: The first-trimester maternal serum level of 25(OH)D is not altered 
in women with type 2 diabetes, those who develop GDM or those who deliver LGA 
neonates.