**3. Leptin in normal pregnancy**

### **3.1 Source of leptin in pregnancy**

Placenta is the other leptin producing tissue in humans apart from adipose tissue and compelling evidence suggests that both leptin hormone and leptin receptors are expressed in human placenta [1, 8–10]. Leptin is produced by the syncytiotrophoblast cells of the placenta (contribute 95% of total placental leptin) and the vascular endothelial cells on the fetal side (5%) [8, 11, 12]. The amniocytes of the amniotic membrane and the maternal decidua also release leptin into the amniotic fluid [13].

Even though pregnancy is a state of enhanced fat stores, the major proportion of leptin in maternal circulation is contributed by the placenta [1, 11]. Leptin has both endocrine and autocrine actions in the placenta and placental leptin is similar to its adipose tissue derived counterpart in terms of structure and function [10, 11, 14].

Increased blood levels of leptin (by two folds) have been demonstrated in pregnant as compared to non-pregnant women [8]. Presence of leptin has been observed *Leptin and Female Reproductive Health DOI: http://dx.doi.org/10.5772/intechopen.101226*

in placenta from 7 weeks of gestation onwards. Leptin levels increase by 30% at as early as 12 weeks of gestation, plateau at mid pregnancy and return to pre-pregnant levels 24 hours after delivery [8, 11]. The clarification for increased leptin concentration during pregnancy is the release of plasma soluble leptin receptors by the placenta which bind the circulating leptin, hence delaying its clearance [1, 11].
