Table 2.

Summary of Creatine Metabolism in the Human Placenta.

Study	Condition	Gestation	Creatine and Phosphocreatine Content	Creatine Kinases	Creatine Synthesis and Transport
Thomure et al. [64]	Healthy	First, second and third trimester		uMt-CK and CKBB gene expression detected. Expression was low in the first and second trimester before a peak at term. CKBB protein expression consistent throughout gestation. uMt-CK expression rose through to mid-gestation before declining just before term.
Ellery et al. [13]	Healthy	First trimester (10–13 weeks’ gestation)			GATM, GAMT and SLC6A8 detected.
Ellery et al. [13,65]	Healthy	Third trimester			AGAT, GAMT and SLC6A8 gene and protein detected. GATM expression and GAA tissue content decreased with advancing gestational age and birth weight.
Tissot et al. [69]	High altitude	Term	Increased phosphocreatine levels detected.
Ellery et al. [13]	FGR	Third trimester	43% higher total creatine content compared to gestation-matched controls.		2-fold increase in SLC6A8 expression.
Ellery et al. [14]	PE	Third trimester	38% higher total creatine content compared to gestation-matched controls.	Increased CKBB mRNA expression.	Increased GATM, GAMT, SLC6A8 mRNA expression.
Jääskeläinen et al. [71]	PE	Term	Increase in creatine concentration in venous cord plasma at delivery.
McMinn et al. [74]	FGR	Term			Down-regulation in GATM.

Abbreviations—fetal growth restriction (FGR), preeclampsia (PE), cytosolic brain-type creatine kinase (CKBB), ubiquitous mitochondrial creatine (uMt-CK), the creatine transporter (SLC6A8), guanidinoacetate (GAA), arginine:glycine amidinotransferase (AGAT translated from the GATM gene), guanidinoacetate methyltransferase (GAMT).