European Journal of Obstetrics & Gynecology and Reproductive Biology 136 (2008) 146–150 www.elsevier.com/locate/ejogrb

Review

The role of leptin in fetal growth: A short review from conception to delivery Sorina Grisaru-Granovsky a, Arnon Samueloff a, Deborah Elstein b,* a

Department of Obstetrics and Gynecology, Shaare Zedek Medical Center, Jerusalem, Israel b Gaucher Clinic, Shaare Zedek Medical Center, Jerusalem 91031, Israel Received 21 January 2007; received in revised form 13 June 2007; accepted 16 June 2007

Abstract Abnormally high- or low-serum maternal levels and/or levels in placental, umbilical blood, and fetus/neonate are associated with a wide spectrum of complicated pregnancies. Whereas the state of knowledge about mechanisms and pathways involving secondary or tertiary modulators is far from complete, the role of leptin from ovulation and implantation and throughout pregnancy underscores its importance in normal and abnormal states. # 2007 Elsevier Ireland Ltd. All rights reserved. Keywords: Adipokines; Conception; Fertility; Intrauterine growth failure; Leptin; Pre-eclampsia; Pregnancy; Reproduction

Contents 1. 2. 3. 4.

5.

Introduction . . . . . . . . . . . . . . . . . . . . Leptin and fertility . . . . . . . . . . . . . . . . Leptin and ovulation . . . . . . . . . . . . . . Leptin in pregnancy . . . . . . . . . . . . . . . 4.1. Leptin in pregnancies complicated 4.2. Leptin in pregnancies complicated 4.3. Leptin in multi-fetal pregnancies . Summary . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . .

........................ ........................ ........................ ........................ by gestational diabetes. . . . . . . . by pre-eclampsia and intrauterine ........................ ........................ ........................

1. Introduction There is increasing interest in links between body fat and reproduction. During the past decade, advances in molecular technology and improved understanding of leptin, one of the secretory products of the adipose cell [1], have resulted in a more sophisticated appreciation of the mechanisms that control satiety and obesity, energy homeostasis, and even bone metabolism. Similarly, recognition of a role for leptin * Corresponding author. Tel.: +972 2 6555093; fax: +972 2 6517979. E-mail address: [email protected] (D. Elstein).

............. ............. ............. ............. ............. growth restriction ............. ............. .............

. . . . . . . . .

. . . . . . . . .

. . . . . . . . .

. . . . . . . . .

. . . . . . . . .

. . . . . . . . .

. . . . . . . . .

. . . . . . . . .

. . . . . . . . .

. . . . . . . . .

. . . . . . . . .

. . . . . . . . .

. . . . . . . . .

. . . . . . . . .

. . . . . . . . .

. . . . . . . . .

. . . . . . . . .

. . . . . . . . .

. . . . . . . . .

. . . . . . . . .

. . . . . . . . .

146 147 147 148 148 148 149 149 149

in reproductive physiology has stimulated research at every level from ovulation, to conception and delivery [2]. Among the early pieces of evidence that implicate involvement of leptin in reproduction is the role of leptin in triggering puberty, underscoring the connection between adequate energy stores (the ‘‘critical weight’’ theory) and reproductive capacity [3]. Low levels of leptin may be regarded as a ‘‘starvation signal’’ protecting against insufficient energy stores. The reduction of leptin with starvation causes a decrease in the gonadal-thyroid axis while stimulating the adrenal axis. These changes, under experimental conditions, are prevented by administration of

0301-2115/$ – see front matter # 2007 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.ejogrb.2007.06.021

S. Grisaru-Granovsky et al. / European Journal of Obstetrics & Gynecology and Reproductive Biology 136 (2008) 146–150

leptin, suggesting that leptin serves as a neuroregulator of reproductive function. Furthermore, administration of leptin in non-human primates accelerates puberty and in normal human children leptin levels increase as body fat mass increases before puberty. In contrast children with inactivating mutations of the leptin receptor are obese, remain prepubertal and suffer from hypogonadotrophic hypogonadism. Moreover, leptin is more intimately critical to reproduction because of its specific production in human placenta [4]. Placental insufficiency is associated with a significant increase in placental leptin production, suggesting that leptin may be an index of fetal stress and placental dysfunction [5] as a marker of the inflammatory response of the placenta and not only as a function of the placental weight. Fetal production of leptin [6] has been shown to be a putative marker of body mass of the human fetus. In sheep, leptin mRNA is detectable in fetal adipose tissue by approximately 90 days gestation; leptin levels then increase up to term and correlate with fetal weight, suggesting that the production of leptin mRNA is modulated by an increase in the number and size of adipocytes. This correlation is integrated into the concept of the ‘‘fetal origin of adult diseases’’: fetal fat tissue dysregulation may be the advent of a life-long risk for obesity with its own attendant risks [7]. Thus, leptin is a critical element in maternal–placental–fetal interactions, and certainly via pathways not envisioned a decade ago, because its effects are not limited to adipose cell metabolism alone. The purpose of this paper is to review the most recent literature relating leptin specifically to human reproduction (because it has not yet been proven unequivocably that findings in non-human systems will be equivalent to what is seen in humans).

2. Leptin and fertility Leptin has central effects in males and females via hypothalamic and pituitary feedback mechanisms, and because leptin is a facilitator of gonadotropin releasing hormone (GnRH) expression [8]. One of the proposed mechanisms of this action is that leptin increases oxidative metabolic and fatty acid oxidation in peripheral tissue both by a direct effect and by a sympathetic-mediated effect; the latter is associated with activation of activated protein kinase (AMP) and its stimulatory effect on the hypothalamic nuclei. On the other hand, reduced leptin concentrations provoke a signal that initiates a neuroendocrine response to limit procreation. Males exhibit peripheral effects of leptin as well: leptin inhibits testosterone secretion at the testicular level, blunts falling levels of thyroxine (T4), attenuates increases in adrenocorticotropic hormone (ACTH) and glucocorticoids, and also stimulates a peripheral gonadal effect as expressed in sperm and the human ejaculate [9]. The peripheral feedback loop of the androgens suppresses leptin production [10].

147

In females, however, the importance of leptin for fertility and achievement of pregnancy may prove to be extremely complex, partly because of the effects of obesity per se on fertility and achievement of pregnancy. There are several lines of reasoning that connect the increasing percentages of women with infertility with obesity [11]. In essence, the ontological reason to maintain fertility when food is scarce speaks to the involvement of secretory products of adipose tissues in maintaining fertility. During starvation low leptin concentration signals that energy stores are low and that the body should seek food, while when leptin concentrations are adequate, the body may reduce energy stores for the sake of reproduction (the ‘‘disposable soma theory’’). Thus, leptin ‘‘allows’’ procreation when energy stores are not depleted. In obesity, a leptin resistance state develops. This apparently simplistic relationship becomes more complicated in pregnancy since the elevated levels of leptin during pregnancy (see below) do not induce reduced food intake, i.e. pregnancy is also a state of leptin resistance [12] which is separate from the insulin resistance of pregnancy. It is probable that leptin plays a role in obesity-related infertility at the central level via increased neuropeptide-Y levels in the hypothalamus [13] as well as at the level of the ovary or uterus. Decreased circulating leptin and subsequently reduced follicular stimulating hormone (FSH) secretion is also the probable mechanism to achieve post-coital contraception by the use of an anti-progestin (Mifepristone) during the late follicular phase [14].

3. Leptin and ovulation Leptin has a direct effect on ovulation by inducing luteinizing hormone (LH) feedback loop independent ovulation [15], probably by supporting LH pulsatility in response to LH releasing hormone. This is one of the underlying reasons for using human recombinant leptin to restore amenorrhea. There is variation in leptin levels along with the menstrual cycle [16]. Leptin levels increase during the transition from the follicular to the peri-ovulatory phase and peak in the luteal phase. Transition from the luteal to the luteal/follicular phase show a decline in leptin levels back to the follicular levels. Throughout the entire menstrual cycle leptin levels are also continuously correlated with the body mass index of the woman [16]. Leptin plays a part in obesity-related anovulation [17]. In studies of in vitro fertilization (IVF), elevated serum leptin levels during ovarian hyperstimulation negatively correlated with ovarian response evaluated by estradiol production and the number of oocytes retrieved [18]. Leptin concentrations in the follicular fluid were shown to serve as prognostic indicators of success for therapeutic intervention of ovarian hyperstimulation and sperm injection in ICSI procedures [19].

148

S. Grisaru-Granovsky et al. / European Journal of Obstetrics & Gynecology and Reproductive Biology 136 (2008) 146–150

Elevated follicular fluid leptin levels were shown to be of prognostic value in failed IVF conception and intracytoplasmic sperm injection (ICSI) techniques [20], allegedly because leptin and estradiol work in concert in a concentration-dependent manner [21]. In summary, leptin facilitates ovulation directly and replacement therapy may restore function in cases of deficiency.

4. Leptin in pregnancy Serum leptin concentrations begin to increase from the earliest stages of pregnancy [22], implying that the increases are not due merely to maternal weight gain. Leptin in the S-phase of the cell cycle indirectly induces acceleration of trophoblast cell proliferation by inhibiting apoptosis and displacing cells into the G2/M phase of the cell cycle [23]: leptin would then be both trophic and mitogenic in a timeand dose-dependent manner [23]. Leptin has an inhibitory effect on trophoblastic vascular endothelial growth factor (VEGF) secretion (related to angiogenesis) which may be a mechanism of predisposition to late pregnancy complications such as hypertension, pre-eclampsia, and small for gestational age neonates [24]. The fetus too produces leptin beginning early in the mid-trimester [6], but it is the placenta that greatly contributes to maternal hyperleptinenimia [25]. Fetal levels start increasing around the 34th week of gestation [26], and are correlated with fetal weight [26]. After birth, leptin levels drop both in the neonate and postpartum mother [27]. Leptin and its receptor are abundant in the placenta as well as the amnion and chorion. The sustained and progressive increase in leptin over the course of the pregnancy has been suggested mechanistically to be due to increased soluble leptin receptor: more bound leptin in the maternal circulation, the lower the concentrations of unbound leptin for the hypothalamus. The ultimate result of increasing leptin levels during pregnancy, then, is prevention of reduced food/energy intake [22]; leptin therefore is thought to ensure adequate nutrient transfer for placental–fetal use [28]. Among other putatively direct effects of leptin on the growing fetus are enabling fetal weight gain unrelated to other growth factors [29]; stimulation of fetal bone growth [30] and ossification; lipid catabolism, decreasing levels of placental triglycerides and cholesterol [22]; and enhanced fetal lung surfactant production [31] although interestingly, because of the differential effect of leptin on androgens [10], this may explain the difference between male and female babies vis a vis lung development. In normal pregnancies relatively high levels of leptin have been measured in amniotic fluid with an inverse correlation relative to placental and fetal volume in the second trimester. The latter suggests that leptin may be an anti-placental growth hormone or a feedback modulator of substrate supply to the fetus and placenta [32]. Thus, among the purposes of

increased leptin concentrations during pregnancy beyond maintaining the placenta and encouraging nutrient exchange with the fetus, is promotion of normal fetal development, including under conditions of IVF [33]. 4.1. Leptin in pregnancies complicated by gestational diabetes Abnormally high levels of maternal leptin in early pregnancy were shown to be predictive of an increased risk for gestational diabetes mellitus later in the pregnancy [34]. Conversely, gestational diabetes mellitus has been shown to be associated with up-regulation of leptin while macrosomia of neonates of mothers with normal glycemic status was associated with down-regulation of leptin [35]. Nevertheless, umbilical cord plasma leptin levels were higher in infants of diabetic mothers [36]. As a possible explanation, recent studies in term placenta imply that increased expression of leptin mRNA but not that of its receptors, is associated with the diagnosis of gestational diabetes [37]. Leptin expression in placenta, amnion and choriodecidua from normal pregnant women was higher than in samples obtained from women with gestational diabetes mellitus; however, leptin levels from adipose tissue and skeletal muscle from women with gestational diabetes mellitus were greater than from healthy women, demonstrating placental dysregulation of leptin in gestational diabetes mellitus [38]. Thus, these findings point to maternal leptin as a possible modulator of gestational diabetes. 4.2. Leptin in pregnancies complicated by preeclampsia and intrauterine growth restriction Significantly, elevated leptin levels of placental occur in pregnancies complicated by pre-eclampsia [39] and intrauterine growth restriction (IUGR) mostly of placental origin [40]; however, leptin gene expression is higher only in preterm pre-eclampsia [40]. Compared with healthy pregnant control, significant increases in leptin mRNA expression were seen in placenta from pre-eclamptic patients [41] suggestive of a possible early defect in placentation. Moreover, high amniotic fluid leptin levels were noted in the pre-eclamptic pregnant women [42]. In addition, recent studies show that the G-G haplotype of the leptin receptor gene polymorphisms Lys109Arg and Gln223Arg was significantly more represented among severely pre-eclamptic patients relative to controls [43]. Integrating the information available on leptin receptor regulation of soluble leptin availability (see above), this may indicate that leptin levels are involved in modifying the risk for severe pre-eclampsia. Low levels of leptin were observed in blood samples from women with IUGR relative to healthy women [44]. Neonatal leptin levels were also lower in IUGR babies compared to healthy babies, although the levels per kilogram weight were not significantly different [45]; umbilical cord blood leptin

S. Grisaru-Granovsky et al. / European Journal of Obstetrics & Gynecology and Reproductive Biology 136 (2008) 146–150

concentrations were also significantly lower in IUGR cases [46]. These findings confirm that fetal adipose tissue is a source of leptin. Interestingly, babies born to smoking mothers had significantly lower serum leptin levels than other babies [47] that was unrelated to fetal weight, a factor with considerable ramifications (regarding smoking, leptin, and fetal complications). 4.3. Leptin in multi-fetal pregnancies Among early studies of adult twins, it was shown that leptin levels were threefold higher in obese twins than in lean twins [48]. Nonetheless, in human infant twins discordant for weight, fetal plasma leptin levels of the intrauterine growthrestricted twins (discordant monochorionic or dichorionic) were comparable, with a positive correlation between umbilical cord leptin levels and birth weight of the twin pairs [49]. Yet, regardless of chorionicity, umbilical leptin levels in IUGR twins were twofold lower than in normal-sized twins. In normal multi-fetal uncomplicated pregnancies, the umbilical cord leptin levels correlated independently with each individual birth weight of the neonates regardless of the number (twins or triplets) of fetuses [50]. Thus, the multi-fetal model substantiates the fetal lean body weight and the placental contribution to leptin secretion rather than as an independent maternal contribution.

5. Summary Leptin, a secretory product of adipose tissue, has been implicated in endometrial, ovarian and sperm physiology because of its role in puberty and because of its differential effects in the two genders. The relationship of leptin secretion in various modes of assisted reproductive techniques with implantation is currently a field of active basic and clinical research. What is clear is that elevated levels of leptin mark the human pregnancy at the maternal– fetal dyad level. Abnormally high or low serum maternal levels and/or levels in placenta, umbilical cord and neonate are associated with pregnancies complicated by carbohydrate intolerance, hypertension and small for gestational age neonates. The feedback loops, the role of leptin as a stress induced cytokine and its relations to VEGF and its receptors, may provide windows to future research and intervention options.

References [1] Zhang Y, Proenca R, Maffei M, Barone M, Leopold I, Friedman JM. Positional cloning of the mouse obese gene and its human homologue. Nature 1994;372:425–32 [Erratum in: Nature 1995;374;479]. [2] Hassink SG, de Lancey E, Sheslow DV, et al. Placental leptin: an important new growth factor in intrauterine and neonatal development? Pediatrics 1997;100:E1.

149

[3] Chehab FF. The reproductive side of leptin. Nat Med 1997;3:952–3. [4] Masuzaki H, Ogawa Y, Sagawa N, et al. Nonadipose tissue production of leptin: leptin as a novel placenta-derived hormone in humans. Nat Med 1997;3:1029–33. [5] Lepercq J, Guerre-Millo M, Andre J, Cauzac M, Hauguel-de Mouzon S. Leptin: a potential marker of placental insufficiency. Gynecol Obstet Invest 2003;55:151–5. [6] Lepercq J, Challier JC, Guerre-Millo M, Cauzac M, Vidal H, Hauguelde Mouzon S. Prenatal leptin production: evidence that fetal adipose tissue produces leptin. J Clin Endocrinol Metab 2001;86:2409–13. [7] McMillen IC, Edwards LJ, Duffield J, Muhlhausler BS. Regulation of leptin synthesis and secretion before birth: implications for the early programming of adult obesity. Reproduction 2006;131:415–27. [8] Akhter N, Johnson BW, Crane C, et al. Anterior pituitary leptin expression changes in different reproductive states: in vitro stimulation by gonadotropin-releasing hormone. J Histochem Cytochem 2007;55: 151–66. [9] Aquila S, Gentile M, Middea E, et al. Leptin secretion by human ejaculated spermatozoa. J Clin Endocrinol Metab 2005;90:4753–61. [10] Watanobe H, Suda T. A detailed study on the role of sex steroid milieu in determining plasma leptin concentrations in adult male and female rats. Biochem Biophys Res Commun 1999;259:56–9. [11] Mitchell M, Armstrong DT, Robker RL, Norman RJ. Adipokines: implications for female fertility and obesity. Reproduction 2005;130: 583–97. [12] Popovic V, Casanueva FF. Leptin, nutrition and reproduction: new insights. Hormones (Athens) 2002;1:204–17. [13] Magni P, Motta M, Martini L. Leptin: a possible link between food intake, energy expenditure, and reproductive function. Regul Pept 2000;92:51–6. [14] Leminen R, Raivio T, Ranta S, et al. Late follicular phase administration of mifepristone suppresses circulating leptin and FSH— mechanism(s) of action in emergency contraception? Eur J Endocrinol 2005;152:411–8. [15] Musso C, Cochran E, Javor E, Young J, Depaoli AM, Gorden P. The long-term effect of recombinant methionyl human leptin therapy on hyperandrogenism and menstrual function in female and pituitary function in male and female hypoleptinemic lipodystrophic patients. Metabolism 2005;54:255–63. [16] Wunder DM, Yared M, Bersinger NA, Widmer D, Kretschmer R, Birkhauser MH. Serum leptin and C-reactive protein levels in the physiological spontaneous menstrual cycle in reproductive age women. Eur J Endocrinol 2006;155:137–42. [17] Roman EA, Ricci AG, Faletti AG. Leptin enhances ovulation and attenuates the effects produced by food restriction. Mol Cell Endocrinol 2005;242:33–41. [18] Gurbuz B, Yalti S, Ficicioglu C, Tasdemir S. The relation of serum and follicular fluid leptin and ovarian steroid levels in response to induction of ovulation in in vitro fertilization cycles. Eur J Obstet Gynecol Reprod Biol 2005;118:214–8. [19] Nikolettos N, Asimakopoulos B, Nicolettos N, Efthimiadou A, Mourvati E, Demirel C. Evaluation of leptin, interleukin-1beta, tumor necrosis factor-alpha and vascular endothelial growth factor in serum and follicular fluids of women undergoing controlled ovarian hyperstimulation as prognostic markers of ICSI outcome. In Vivo 2004;18:667–73. [20] Asimakopoulos B, Nikolettos N, Papachristou DN, Simopoulou M, Al-Hasani S, Diedrich K. Follicular fluid levels of vascular endothelial growth factor and leptin are associated with pregnancy outcome of normal women participating in intracytoplasmic sperm injection cycles. Physiol Res 2005;54:263–70. [21] Anifandis G, Koutselini E, Louridas K, et al. Estradiol and leptin as conditional prognostic IVF markers. Reproduction 2005;129:531–4. [22] Henson MC, Castracane VD. Leptin in pregnancy: an update. Biol Reprod 2006;74:218–29. [23] Magarinos MP, Sanchez-Margalet V, Kotler M, Calvo JC, Varone CL. Leptin promotes cell proliferation and survival of trophoblastic cells. Biol Reprod 2007;76:203–10.

150

S. Grisaru-Granovsky et al. / European Journal of Obstetrics & Gynecology and Reproductive Biology 136 (2008) 146–150

[24] McCarthy C, Cotter FE, McElwaine S, et al. Altered gene expression patterns in intrauterine growth restriction: potential role of hypoxia. Am J Obstet Gynecol 2007;196. 70.e1-6. [25] Henson MC, Swan KF, O’Neil JS. Expression of placental leptin and leptin receptor transcripts in early pregnancy and at term. Obstet Gynecol 1998;92:1020–8. [26] McMillen IC, Muhlhausler BS, Duffield JA, Yuen BS. Prenatal programming of postnatal obesity: fetal nutrition and the regulation of leptin synthesis and secretion before birth. Proc Nutr Soc 2004;63: 405–12. [27] Jaquet D, Leger J, Levy-Marchal C, Oury JF, Czernichow P. Ontogeny of leptin in human fetuses and newborns: effect of intrauterine growth retardation on serum leptin concentrations. J Clin Endocrinol Metab 1998;83:1243–6. [28] White V, Gonzalez E, Capobianco E, et al. Leptin modulates nitric oxide production and lipid metabolism in human placenta. Reprod Fertil Dev 2006;18:425–32. [29] Christou H, Connors JM, Ziotopoulou M, et al. Cord blood leptin and insulin-like growth factor levels are independent predictors of fetal growth. J Clin Endocrinol Metab 2001;86:935–8. [30] Ogueh O, Sooranna S, Nicolaides KH, Johnson MR. The relationship between leptin concentration and bone metabolism in the human fetus. J Clin Endocrinol Metab 2000;85:1997–9. [31] Torday JS, Sun H, Wang L, Torres E, Sunday ME, Rubin LP. Leptin mediates the parathyroid hormone-related protein paracrine stimulation of fetal lung maturation. Am J Physiol Lung Cell Mol Physiol 2002;282:L405–10. [32] Woelfer B, Hafner E, Metzenbauer M, Schuchter K, Philipp K. The influence of leptin on placental and fetal volume measured by threedimensional ultrasound in the second trimester. Placenta 2005;26: 124–8. [33] Anifandis G, Koutselini E, Stefanidis I, et al. Serum and follicular fluid leptin levels are correlated with human embryo quality. Reproduction 2005;130:917–21. [34] Qiu C, Williams MA, Vadachkoria S, Frederick IO, Luthy DA. Increased maternal plasma leptin in early pregnancy and risk of gestational diabetes mellitus. Obstet Gynecol 2004;103:519–25. [35] Ategbo JM, Grissa O, Yessoufou A, et al. Modulation of adipokines and cytokines in gestational diabetes and macrosomia. J Clin Endocrinol Metab 2006;91:4137–43. [36] Gross GA, Solenberger T, Philpott T, Holcomb Jr WL, Landt M. Plasma leptin concentrations in newborns of diabetic and nondiabetic mothers. Am J Perinatol 1998;15:243–7. [37] Meller M, Qiu C, Vadachkoria S, Abetew DF, Luthy DA, Williams MA. Changes in placental adipocytokine gene expression asso-

[38]

[39]

[40]

[41]

[42]

[43] [44]

[45]

[46]

[47]

[48]

[49]

[50]

ciated with gestational diabetes mellitus. Physiol Res 2006;55: 501–12. Lappas M, Yee K, Permezel M, Rice GE. Release and regulation of leptin, resistin and adiponectin from human placenta, fetal membranes, and maternal adipose tissue and skeletal muscle from normal and gestational diabetes mellitus-complicated pregnancies. J Endocrinol 2005;186:457–65. Lu D, Yang X, Wu Y, Wang H, Huang H, Dong M. Serum adiponectin, leptin and soluble leptin receptor in pre-eclampsia. Int J Gynaecol Obstet 2006;95:121–6. Laivuori H, Gallaher MJ, Collura L, et al. Relationships between maternal plasma leptin, placental leptin mRNA and protein in normal pregnancy, pre-eclampsia and intrauterine growth restriction without pre-eclampsia. Mol Hum Reprod 2006;12:551–6. Meller M, Qiu C, Kuske BT, Abetew DF, Muy-Rivera M, Williams MA. Adipocytokine expression in placentas from pre-eclamptic and chronic hypertensive patients. Gynecol Endocrinol 2006;22:267–73. Chan TF, Su JH, Chung YF, Hsu YH, Yeh YT, Yuan SS. Elevated amniotic fluid leptin levels in pregnant women who are destined to develop preeclampsia. Acta Obstet Gynecol Scand 2006;85:171–4. Rigo J, Szendei G, Rosta K, et al. Leptin receptor gene polymorphisms in severely pre-eclamptic women. Gynecol Endocrinol 2006;22:521–5. Karowicz-Bilinska A. Leptin concentration in women with normal pregnancy and intrauterine growth retardation [article in Polish]. Ginekol Pol 2004;75:10–4. Arslan M, Yazici G, Erdem A, Erdem M, Arslan EO, Himmetoglu O. Endothelin 1 and leptin in the pathophysiology of intrauterine growth restriction. Int J Gynaecol Obstet 2004;84:120–6. Pighetti M, Tommaselli GA, D’Elia A, et al. Maternal serum and umbilical cord blood leptin concentrations with fetal growth restriction. Obstet Gynecol 2003;102:535–43. Ozkan B, Ermis B, Tastekin A, Doneray H, Yildirim A, Ors R. Effect of smoking on neonatal and maternal serum and breast milk leptin levels. Endocr Res 2005;31:177–83. Grisaru-Granovsky S, Eitan R, Algur N, Schimmel MS, Diamant YZ, Samueloff A. Maternal and umbilical cord serum leptin concentrations in small-for-gestational-age and in appropriate-for-gestational-age neonates: a maternal, fetal, or placental contribution? Biol Neonate 2003;84:67–72. Ronnemaa T, Karonen SL, Rissanen A, Koskenvuo M, Koivisto VA. Relation between plasma leptin levels and measures of body fat in identical twins discordant for obesity. Ann Intern Med 1997;126: 26–31. Sooranna SR, Ward S, Bajoria R. Fetal leptin influences birth weight in twins with discordant growth. Pediatr Res 2001;49:667–72.