**2. Leptin: Structure and function**

Leptin (derivative of Greek word "leptos" which means thin) is an adipose tissue derived hormone. It a known biomarker of adiposity, its levels rising proportionately with body fat stores [3, 8].

Leptin comprises a 167 amino acid polypeptide chain. This 16 kDa protein is encoded by the obesity gene (Lepob gene) situated on chromosome 7 [2, 8].

The preliminary function of leptin was recognised to control energy homeostasis via a negative feedback mechanism to the brain, to reduce the intake of food when the body fat stores were sufficient [3, 9].

However, recent literature elucidates that leptin can control and regulate the functioning of HPO axis, has a putative role as a placental hormone and can directly affect the reproductive function of gonads.

In this chapter, the role of leptin in female reproductive health will be illustrated under the following sections:

a.Leptin in normal pregnancy

b.Leptin in pathological pregnancy:

i.Pre-eclampsia (PE)

ii. Gestational diabetes mellitus (GDM)

iii.Fetal growth restriction (FGR)

c.Leptin in puberty and infertility

d.Leptin in menstruation

e.Leptin in PCOS

f. Leptin in recurrent pregnancy loss (RPL).
