Table 1. Gestational diabetes mellitus predictors and biomarkers.

	Pregnancy period	Values in GDM pregnancy	References
Conventional predictors
Impaired glucose tolerance	Between weeks 24 and 28	Assessed by OGTT: fasting > 5.1 mmol/L, 1st hour > 10 mmol/L or 2nd hour > 8.5 mmol/L	15-17
Glycated haemoglobin	NA	> 6.5% (48 mmol/mol)	24
Body mass index	NA	> 30 kg/m2	7
History of GDM	NA	positive	7
Conventional GDM biomarkers
Fasting plasma glucose	Early pregnancy	> 5 mmol/L, > 4.7 mmol/L or > 4.5 mmol/L	23,25-27
Hormones involved in energy homeostasis
C-peptide	NA	C-peptide	30,31
Fasting insulin	NA	insulin	30,31
Impaired insulin sensitivity	NA	Deviation from normal insulin concentrations assessed by measurement of fasting insulin and OGTT insulin (or 2 h postprandial insulin)	28
Homeostatic Model Assessment of Insulin Resistance	NA	Insufficient as a predictive marker for GDM	7
SHBG	Before and in early pregnancy	Ż SHBG	5
Leptin	During the whole pregnancy (because of placental production)	leptin	2
Adiponectin	In the first and second trimester	Ż adiponectin among women who develop GDM in the third trimester	2,5
Amino acid profile
Branched amino acids	In the first trimester; also valine, leucine and isoleucine in the second and third trimesters	valine, leucine and isoleucine	36-38
Aromatic amino acids	In the third trimester	phenylalanine and tyrosine	98
Sulfur-containing amino acids	NA	methionine, contradictory findings for cystine and homocysteine	18,40,41
Arginine	In the first trimester	arginine	42
Glycine	In the first trimester	Contradictory findings	42
Other amino acids	NA	When asparagine, threonine, aspartate, phenylalanine, glutamine risk of GDM is increased	43
Tryptophan metabolite, serotonin	NA	serotonin	44,45
Fatty acids
Long chain polyunsaturated fatty acids and essential fatty acids	NA	Ż placental uptake	46
FFA	NA	FFA	47
Inflammatory biomarkers
C-reactive protein (CRP) or highly sensitive C-reactive protein (hs-CRP)	NA	CRP, hs-CRP; not specific to pregnancy	2,5,7
	Pregnancy period	Values in GDM pregnancy	References
Tumour necrosis factor alpha	NA	Contradictory findings	53,57,58
Interleukin-6	NA	Contradictory findings	53,57,58
Whole blood parameters (not specific for pregnancy)
Blood cell count (erythrocytes, leukocytes, neutrophils, lymphocytes and monocytes)	NA	blood cell count	12,59
MCV and MCH	NA	Ż MCV and MCH	59
Ratio of blood cells (e.g., NLR or MLR)	NA	NLR, MLR	11,60-62
Platelet count	NA	platelet count	59
MPV	NA	Ż MPV	59
Ratio of pro-inflammatory T-helpers (Th1 and Th17) and anti-inflammatory cells (T regulatory cells, Treg, and Th2)	NA	ratio Th1 and Th17 to Treg and Th2	63
CD3+, CD4+, CD8+	NA	CD3+, CD4+, CD8+	65,66,67
Novel GDM biomarkers
BNP	NA	Ż BNP	5
Afamin	First trimester	afamin	68
FGF21	First trimester	FGF21	69
ANGPTL8	Early pregnancy	ANGPTL8	70
Placental lactogen	NA	placental lactogen	71
Galanin	Second trimester	galanin	72
VAP1	Second trimester	VAP1	73
FABP4	Second trimester	FABP4	74
Fetuin-A or AHSG	In the first and second trimester	fetuin-A	78-82
pGCD59	Prior week 20	pGCD59	95
Extracellular vesicles	Between weeks 11 and 14	Characteristic content, further research necessary	75,77
Maternal microbiota	NA	Contradictory findings, better used as monitoring tool	85-92
PIGF	Early pregnancy	PIGF	96,97
GDM - gestational diabetes mellitus. NA - not applicable. OGTT - oral glucose tolerance test. SHBG - sex hormone-binding protein. FFA - free fatty acids. CRP - C-reactive protein. hs-CRP - high sensitive C-reactive protein. MCV - mean corpuscular volume. MCH -mean corpuscular haemoglobin. NLR - neutrophil to lymphocyte ratio. MLR - monocyte to lymphocyte ratio. MPV - mean platelet volume. Th - inflammatory T-helpers. CD - cluster of differentiation. BNP - brain natriuretic peptide. FGF21 - fibroblast growth factor 21. ANGPTL8 - angiopoietin-like protein 8. VAP1 - vascular adhesion protein 1. FABP4 - fatty acid-binding protein 4. AHSG - α2-Heremans-Schmid glycoprotein. pGCD59 - plasma glycated CD59. PIGF - placenta growth factor.