“…Antipyrine diffuses rapidly, equilibrating between the two circuits, while creatinine, a hydrophilic molecule, diffuses more slowly across the placenta. The transport of antipyrine is flow limited [70][71][72]76], while creatinine transfer is limited by its hydrophilic property and transferred through extra-cellular pathways [76][77][78]. Antipyrine and creatinine are generally used to normalize data across multiple experiments [28].…”