Hum. Reprod. Advance Access published online on February 15, 2008
Human Reproduction, doi:10.1093/humrep/den020
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Maternal serum ghrelin levels in early IVF pregnancies: lack of prognostic value for viable pregnancy and altered post-prandial responses
1 Instituto Universitario Valenciano de Infertilidad IVI Valencia, University of Valencia, Plaza Policía Local, 3, 46015 Valencia, Spain 2 Department of Cell Biology, Physiology and Immunology, University of Córdoba, 14004 Córdoba, Spain 3 CIBER (CB06/03) Fisiopatología de la Obesidad y Nutrición, Instituto Salud Carlos III, 28029 Madrid, Spain
4 Correspondence address. E-mail: c.vidal{at}ivi.es
 |
Abstract |
|---|
 Top Abstract IntroductionMaterials and MethodsResultsDiscussionFundingReferences |
|---|
BACKGROUND: Ghrelin is a pleiotropic hormone, involved in the control of growth and metabolism, whose circulating levels fluctuate in relation to food intake and body mass index. Ghrelin has been detected in the decidualized endometrium, as well as in human and rat placenta.
METHODS: A total of 106 patients undergoing IVF procedures were prospectively recruited. On Days 16 and 23 after oocyte retrieval, the patients were subjected to blood sampling after overnight fasting, for determination of serum ghrelin, hCGβ and progesterone levels. In addition, ghrelin levels were assayed in these groups, 2 h after ingestion of a fixed-calorie meal.
RESULTS: The subjects were divided according to whether they achieved an ongoing pregnancy. On Days 16 and 23 after oocyte retrieval, pre-prandial serum ghrelin levels were not statistically different, although a general trend toward a decrease in circulating ghrelin by Day 23 was detected in pregnant groups. Although in non-conceiving subjects, maternal ghrelin levels showed an expected 15% decline after meal ingestion, such a post-prandial decrease was not statistically significant in pregnant women, selectively on Day 16 after oocyte retrieval.
CONCLUSIONS: Maternal ghrelin levels at early gestational age do not appear to pose diagnostic (as marker) or prognostic value for pregnancy outcome in IVF procedures.
Key words: ghrelin/progesterone/human choriogonadotrophin (hCG)/assisted reproduction techniques/early pregnancy
|
Introduction |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionFundingReferences |
|---|
Despite recent progress in the field, assisted reproduction techniques (ART) are stressful and invasive. Of note, <40% of the transferred embryos successfully implant and develop into an ongoing pregnancy. Moreover, IVF appears to be associated with an increased risk of adverse gestational outcome, including spontaneous abortion and ectopic pregnancy (Van Voorhis, 2007
). Because of the above uncertainties, identification and validation of early predictors of pregnancy outcome in IVF procedures are eagerly needed.
In this context, extensive efforts have been devoted to identify reliable markers capable to distinguish between viable and non-viable pregnancies before direct verification of intrauterine pregnancy becomes possible by means of trans-vaginal sonography (TVS). Thus, a wide array of molecules has been studied as earlier markers of pregnancy, as well as prognostic factors for the IVF outcome. These include, among others, hCGβ, CA-125, progesterone and other sex steroids hormones, inhibin-A, cytokines, adhesion molecules and several neuropeptides (Hauzman et al., 2004; Mueller et al., 2004; Ioannidis et al., 2005; Urbancsek et al.; 2005).
The peptide hormone ghrelin was isolated as the endogenous ligand for the GH secretagogue receptor (GHS-R) (Caminos et al., 2003; Kojima et al., 1999). Although it was originally identified in the context of growth control, soon after its cloning, it became evident that ghrelin is a rather pleiotropic regulator involved in a wide variety of biological functions, including regulation of food intake and metabolism. Indeed, circulating ghrelin levels fluctuate in relation to meal intake and negatively correlate with body mass index (Korbonits et al., 2004; Van der Lely et al., 2004), leading to the hypothesis that ghrelin may operate as orexigenic factor that signals for energy insufficiency, a phenomenon that has drawn considerable attention (Zigman and Elmquist, 2003). On the contrary, the potential role of ghrelin in the control of reproductive functions has so far remained mostly neglected. Yet, fragmentary evidence strongly suggests that ghrelin may be involved in the modulation of several aspects of reproduction, including regulation of gonadal function and gonadotrophin secretion (Barreiro and Tena-Sempere, 2004; Tena-Sempere, 2005).
In this scenario, a potential role for ghrelin in pregnancy has emerged, based on the observation that ghrelin is highly expressed in first trimester human placenta as well as in rat placental tissue (Gualillo et al., 2001). Moreover, expression of ghrelin and GHS-R genes was also described in decidualized endometrium on non-conceivers, and ghrelin has been proposed as a paracrine/autocrine regulator of decidualization of human endometrial stromal cells, potentially involved in the cross-talk between endometrium and embryo during implantation (Tanaka et al., 2003). Yet, despite the proven placental expression of ghrelin and the known metabolic alterations linked to pregnancy, potential changes in circulating ghrelin levels at early stages of gestation have not been analyzed.
In this study, we prospectively evaluated pre-prandial serum ghrelin levels in a large cohort of women, undergoing different IVF procedures, at Days 16 and 23 after oocyte retrieval, and correlated these values with the circulating concentrations of known markers of high diagnostic and prognostic value, such as hCGβ and progesterone. In addition, given the profound metabolic adaptations that take place with gestation, post-prandial responses in terms of serum ghrelin levels were determined in early pregnancy.
|
Materials and Methods |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionFundingReferences |
|---|
Subjects
Thirty eight participants (35.8%) failed to conceive after embryo transfer. This study was approved by the Research Ethics Committee of the IVI Institute (Valencia, Spain). A total of 106 women, who underwent embryo transfer at our Institution between June and October 2004, were enrolled in this study after written consent agreement. The patients underwent either IVF, ICSI or oocyte donation, according to previously described protocols (Escudero et al., 2004
; Soares et al., 2005). Three groups of women were defined according to pregnancy outcome: non-conceivers (levels of β-hCG < 10 IU/l on Day 16 after oocyte retrieval), abnormal pregnancy (biochemical, spontaneous abortion or ectopic) or viable/clinical intrauterine pregnancy (singleton or twin). In detail, for the latter two groups, women with β-hCG levels > 10 IU/l at Day 16 were followed up with blood tests on Day 23 and weekly TVS until 8 weeks of pregnancy, when they were either catalogued as having normal pregnancy or were diagnosed with spontaneous abortion or ectopic pregnancy.
Protocol
In all subjects, an initial blood sample was obtained in the morning between 8.00 and 9.00 a.m., after an overnight fasting. Blood samples were drawn in standard serum separator tubes and were allowed to clot before centrifugation at 3000g for 10 min. The serum fractions were stored at –80°C until use for hormone measurements. After initial blood sampling, all the patients were provided with a standardized meal and drink, to assess potential changes in ghrelin concentrations, as circulating ghrelin levels have been shown to be modulated by food intake (Cummings et al., 2001). This meal included one coffee with milk and sugar, toast with jam and an orange juice (total of 347 kcal; of which 8 g of proteins, 19 g of fats and 31 g of carbohydrates). Two hours after the first sample, all women underwent a second blood extraction, following the procedures described above.
Hormone measurements
Ghrelin
Total ghrelin levels were measured in serum samples from the different experimental groups using a commercial radioimmunoassay kit from Phoenix Pharmaceuticals (Belmont, CA, USA), following the instructions of the manufacturer. This system equally recognizes the acylated (octanoyl group at Ser-3) and un-acylated forms of human ghrelin, with no cross-reactivity with a large array of structurally related or unrelated neuropeptides or ghrelin fragments (for details see www.phoenixpeptide.com/qcdata/RIK/protocolGhrelin.htm). As reported by the manufacturer, the detection limit for the assay was 
6.4 pg/tube. The inter-assay coefficient of variation was below 5%. All experimental samples were measured in the same assay.
Progesterone and hCGβ
Serum progesterone levels were analyzed with sequential competitive immunoassay (AxSYM; Abbott Laboratories, Abbott Park, IL, USA), following the instructions of the manufacturer. Serum levels of hCGβ were assayed using a microparticle enzyme immunoassay (AxSYM; Abbott Laboratories). The sensitivity of both assays was 2 IU/l, with coefficients of variation of 4.1–6.6%, respectively.
Statistical analysis
Hormonal data are presented as mean ± SEM. Results were analyzed for statistically significant differences using two-way ANOVA, for comparison of hormonal levels in the pre-prandial state among the different pregnancy groups and at the two time-points (Days 16 and 23) assayed, by following the procedures of the software package SigmaStat 2.0 (Jandel Corp., San Rafael, CA, USA). In addition, paired Student's t-tests were used for specific statistical comparison of pre- and post-prandial ghrelin levels within each group. P-values 
0.05 were considered statistically significant.
|
Results |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionFundingReferences |
|---|
There were 106 women who completed IVF/ICSI/oocyte donation and embryo transfer at the Instituto Valenciano de Infertilidad (IVI) and who were included in the study. The general characteristics of the participants are presented in Table I. No significant differences were detected in terms of age of individuals, body mass index, number of oocytes retrieved or number of embryos transferred during the IVF cycles among the groups. The overall pregnancy rate in this cohort was 64% per embryo transfer (n = 68 pregnancies); this was reduced to
55% after exclusion of biochemical pregnancies, in line with previously published rates from our Institution (Melo et al., 2006; Alvarez et al., 2007). There were 52 women (49.0%) had a viable intrauterine pregnancy at week 8 of gestation (clinical or ongoing pregnancy), of which 28 were singleton pregnancies (26.4%) and 24 were twin pregnancies (22.6%). In addition, 16 individuals (15.1%) had an abnormal pregnancy, of which nine (8.4%) were biochemical and seven (6.6%) were spontaneous abortions. Ectopic pregnancies did not occur in this cohort. There were 38 participants (35.8%) failed to conceive after embryo transfer.
|
At Day 16 after oocyte retrieval, pre-prandial serum ghrelin levels were not statistically different between non-conceiving women (used as references), clinical pregnancies, either singleton or twin gestations, biochemical pregnancies and spontaneous abortions (Table II). Of note, however, a trend toward a decrease in mean fasting ghrelin concentrations (of
9–11%), which did not reach statistical significance, was noticed in all pregnant groups, except for twin pregnancies. Moreover, a similar tendency was detected at Day 23 after oocyte retrieval (compared with values of non-conceiving women at Day 16). In clear contrast, serum hCGβ levels dramatically increased at Day 16 in all pregnant subjects as expected, with maximal values in twin pregnancies, which doubled those of single gestations, and the lowest elevation was seen in biochemical pregnancies, as shown in Table II. At Day 23 after oocyte retrieval, hCGβ levels had further increased as a reflection of the progression of pregnancy. Again, the magnitude of such an increase was maximal in twin pregnancies, whereas hCGβ concentrations were significantly lower in gestations with abnormal development, leading to spontaneous abortion by the end of week 8 of pregnancy. Finally, a significant elevation in serum progesterone levels was also observed in pregnant women at Day 16 after oocyte retrieval, as expected. Yet, the magnitude of such an increase was similar between single and twin pregnancies, whereas it was lower in biochemical gestations and negligible in spontaneous abortions (Table II). In contrast to hCGβ, serum progesterone concentrations were not further increased at Day 23, but remained stable in viable clinical pregnancies.
|
To comparatively evaluate the potential value of pre-prandial serum ghrelin levels as an early predictor of a viable pregnancy, in Table III we present a compilation of the relative variations (fold-increase), between Day 16 and Day 23 after oocyte retrieval, in serum ghrelin, hCGβ and progesterone concentrations in the different pregnant groups. Neither ghrelin nor progesterone levels changed (over corresponding values at Day 16) in any of the pregnant groups. In contrast, the relative increase in serum hCGβ concentrations between Day 16 and Day 23 detected in ongoing clinical pregnancies nearly doubled that detected in abnormal pregnancies leading to spontaneous abortion. The proportional increase in hCGβ levels was similar between single and twin pregnancies. As no determinations were conducted in biochemical pregnancies at Day 23, this analysis could not be conducted in that group.
|
Finally, the effects of meal intake on serum ghrelin levels were evaluated in early pregnancy (Day 16 and Day 23 after oocyte retrieval); the responses in women who failed to conceive, as detected on Day 16, were used as a reference control for both time-points. In non-conceiving women, the intake of a fixed-calorie meal (total of 347 kcal; of which 8 g was proteins, 19 g was fats and 31 g was carbohydrates) induced a significant decrease in circulating ghrelin levels at 2 h after ingestion (282.0 ± 13.6 versus 329.6 ± 14.4 pg/ml in pre-prandial state; P < 0.05), accounting for a 15% decrease compared with corresponding baseline levels. In contrast, on Day 16 after oocyte retrieval, marginal, non-significant decreases in serum ghrelin levels were observed 2 h after meal intake both in single (278.0 ± 10.6 versus 299.5 ± 10.8 pg/ml in pre-prandial state; NS) and in twin pregnancies (301.4 ± 15.8 versus 328.2 ± 18.8 pg/ml in pre-prandial state; NS), accounting for 6% and 8% decreases compared with corresponding baseline levels, respectively. Likewise, in biochemical pregnancies, the magnitude of the meal-induced decrease of ghrelin levels did not reach statistical significance (266.0 ± 22.1 versus 299.6 ± 28.0 pg/ml in pre-prandial state; a 10% decrease compared with corresponding baseline levels). In contrast, in pregnancies leading to spontaneous abortion, the meal intake evoked an
15% decrease in mean ghrelin levels over corresponding baseline values; this decrease (in absolute values) reached statistical significance (248.0 ± 12.4 versus 294.0 ± 13.6 pg/ml in pre-prandial state; P < 0.05).
In contrast to the earlier stage, on Day 23 after oocyte retrieval, fixed-calorie meal intake in pregnant women evoked a significant decrease in circulating ghrelin levels, both in single (252.4 ± 14.2 versus 290.4 ± 12.2 pg/ml in pre-prandial state; P < 0.05) and in twin pregnancies (254.0 ± 13.0 versus 311.4 ± 15.8 pg/ml in pre-prandial state; P < 0.05). These represented 14% and 19% decreases compared with corresponding baseline levels, respectively. Similarly, on Day 23, in abnormal pregnancies leading to spontaneous abortion, meal intake evoked an 11% decrease in mean ghrelin levels over corresponding baseline values; yet, due to the reduced number of cases and certain degree of variability among samples, this difference did not reach statistical significance (275.0 ± 17.6 versus 242.6 ± 22.0 pg/ml in pre-prandial state).
|
Discussion |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionFundingReferences |
|---|
In the present study, we have evaluated changes in circulating ghrelin levels at early stages of IVF pregnancies, as well as potential modifications of ghrelin responses to meal intake during the first weeks of gestation. The rationale for these analyses was 2-fold. First, significant expression of ghrelin (at the mRNA and/or protein level) has been documented in the first trimester placenta (with very prominent ghrelin immunoreactivity compared with later stages of gestation), as well as in the decidualized endometrium (Gualillo et al., 2001
; Tanaka et al., 2003), thus making it possible that changes in circulating ghrelin might occur in early stages of pregnancy. Secondly, despite the documented changes in ghrelin secretion and regulation at mid- and late-pregnancy in rodents and humans (as example see Makino et al., 2002; Shibata et al., 2004; Fuglsang et al., 2005), to our knowledge, no study had addressed the possibility of altered secretion of ghrelin at early stages of human gestation, which are defined by significant hormonal and metabolic adaptations.
Concerning pre-prandial ghrelin levels, our hypothesis was that the appearance of a ghrelin-producing tissue, such as the placenta, might lead to detectable increases in circulating levels of ghrelin, whose magnitude might depend on placental viability (thus, potentially serving as surrogate index of pregnancy outcome at early stages of gestation). Indeed, endocrine function of human placenta starts at very early stages of pregnancy (Petraglia et al., 1998), as reflected by the presence of hCGβ in circulation as soon as 8–9 days post-oocyte release in case of successful fertilization and implantation. However, contrary to our expectations, we were unable to detect any significant rise in serum ghrelin concentrations, when compared with women who failed to conceive after IVF. In fact, a consistent trend toward a decrease in serum ghrelin levels, which did not reach statistical significance, was detected in all pregnant groups, except for twin pregnancies, at Day 16 after oocyte retrieval. Moreover, further decreases in mean ghrelin values were observed at Day 23. Although such a tendency (10% compared with baseline levels in non-conceiving women) must be interpreted with caution, our present data complement previous observations on changes in circulating ghrelin along human pregnancy. Thus, Makino et al. (2002) reported that plasma ghrelin concentrations are significantly decreased in normal pregnancy during the third trimester, when compared with non-conceiving women; a finding that has been recently confirmed (Fuglsang et al., 2005). In such a scenario, it is tempting to hypothesize that ghrelin secretion appears to be variably repressed during pregnancy, although the magnitude of such a suppression ranges from marginal (at early stages of pregnancy) to significant (40–45% suppression, according to Makino et al., 2002) in late pregnancy. Interestingly, the reduction in circulating ghrelin in third-trimester pregnancy has been linked to the concomitant elevation in maternal weight and is inversely related with the increase in circulating of placental growth hormone (PGH) (Fuglsang et al., 2005). If of any relevance, the observed, marginal reduction in mean ghrelin levels at early stages of gestation cannot be associated with such factors, suggesting the involvement of different regulatory signals along pregnancy. Notwithstanding, the fact that ghrelin concentrations in early twin pregnancies, which are associated with larger placental mass, were invariantly higher than in other pregnant groups, makes it tempting to suggest that placental production of ghrelin could modestly contribute to the circulating pool of hormone; although this possibility is yet to be confirmed.
The predictive value of ghrelin, as marker of pregnancy outcome, was further assessed by comparing changes in its serum levels, at Days 16 and 23 of pregnancy, with those of hCGβ and progesterone in the different groups. Contrary to the trend toward a decrease in serum ghrelin, circulating levels of hCGβ dramatically increased at very early gestation as expected, with a graded distribution among the groups, ranging from maximum concentrations in twin pregnancies to minimal elevations in biochemical pregnancies, with abnormal pregnancies leading to spontaneous abortion having hCGβ levels which were statistically similar to those of single gestations at Day 16. Moreover, hCGβ levels steadily increased between Day 16 and Day 23 in pregnant and spontaneous abortion groups. However, on Day 23, absolute concentrations and relative increases in hCGβ levels were significantly lower in spontaneous abortions when compared with ongoing pregnancies. In addition, serum progesterone levels significantly increased at early stages (Day 16) in pregnant women and the magnitude of such an increase was significantly lower in biochemical pregnancies. In contrast, abnormal pregnancies leading to spontaneous abortion showed negligible changes in serum progesterone. This confirms recent observations suggesting that single serum progesterone determinations may be a useful early indicator of pregnancy outcome, as higher levels were observed in women having a viable intrauterine pregnancy, as early as Day 14 after oocyte retrieval (Ioannidis et al., 2005).
The characteristics of IVF, as invasive a technique with an increased risk of adverse gestational outcome, have prompted the identification of reliable and early predictors of pregnancy viability. In this context, lower serum inhibin A concentrations have been reported as a more accurate index than hCGβ levels for preclinical abortion after IVF. Yet, no significant differences were detected on the predictive value of hCGβ, inhibin A or their combination in differentiating between ongoing pregnancies (Hauzman et al., 2004). In addition, higher CA-125 concentrations have been suggested to reflect higher endometrial receptivity, but do not predict the number or viability of implanted embryos (Urbancsek et al., 2005). On the other hand, enhanced maternal serum levels of interleukin-2 soluble receptor-
and interferon-
, as early as on Day 11 after embryo transfer, have been associated with poor IVF pregnancy outcome (Fasouliotis et al., 2004). Other placental markers, such as pregnancy-associated plasma protein A (PAPP-A), pregnancy-specific ß2 glycoprotein (SP1) and human placental lactogen (HPL), as well as others non-placental proteins, such as glycodelin, are decreased in ectopic pregnancies when compared with intrauterine pregnancies (Mueller et al., 2004). Conversely, vascular endothelial growth factor is significantly increased in ectopic pregnancies. Our present results cast serious doubts on the potential value of ghrelin levels as a surrogate predictor of pregnancy outcome at early stages of gestation.
Another aspect of ghrelin physiology addressed in our study was the impact of meal intake on circulating ghrelin levels in early gestation. It is well established that ghrelin levels are suppressed post-prandially, with the magnitude of such a suppression being proportional to the ingested caloric load (Callahan et al., 2004). In our study, a significant 15% decrease in mean ghrelin concentrations was detected in non-conceiving subjects (n = 38) 2 h after ingestion of a fixed-calorie meal (347 kcal). Such suppression is fully compatible with that previously reported in a group of 10 healthy volunteers, after an equivalent caloric load (Callahan et al., 2004). Interestingly, no significant suppression of ghrelin levels was detected after meal intake in single and twin pregnancies at Day 16 after oocyte retrieval; mean ghrelin concentrations were only marginally reduced to 6–8% compared with baseline levels. Such a phenomenon (lack of suppression) was not detected in abnormal pregnancies leading to spontaneous abortion and is apparently transient, as consistent; significant decreases in post-prandial ghrelin levels (14–19% versus baseline levels in non-conceiving women) were indeed observed in single and twin pregnancies on Day 23. The functional significance of such a lack of post-prandial suppression of ghrelin levels at very early pregnancy awaits further investigation, but it is interesting to note that the decline in circulating ghrelin levels following food intake has been pointed out as a major component of the signals controlling the episodes of meal ingestion (Callahan et al., 2004).
In summary, we report herein that maternal ghrelin levels, following overnight fasting, at early gestational ages (Days 16 and 23 after oocyte retrieval) do not appear to pose significant diagnostic (as marker) or prognostic value for pregnancy outcome in ART. Our study also identifies a change in the pattern of ghrelin responses to food intake at very early gestation, defined by the lack of post-prandial suppression in serum ghrelin levels after meal ingestion in a large cohort of pregnant women, selectively on Day 16 after oocyte retrieval. Although its functional significance remains to be elucidated, it is tempting to propose that such a phenomenon may represent a previously unknown component of the extensive metabolic adaptations that take place in early pregnancy.
|
Funding |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionFundingReferences |
|---|
This work was supported by grants BFI 2002-00176 and BFI 2005-07446 from DGESIC (Ministerio de Ciencia y Tecnología, Spain) and funds from Instituto de Salud Carlos III (Red de Centros RCMN C03/08 and Project PI042082).
|
References |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionFundingReferences |
|---|
Alvarez C, Alonso-Muriel I, Garcia G, Crespo J, Bellver J, Simon C, Pellicer A. Implantation is apparently unaffected by the dopamine agonist Cabergoline when administered to prevent ovarian hyperstimulation syndrome in women undergoing assisted reproduction treatment: a pilot study. Hum Reprod (2007) doi:10.1093/humrep/dem315.
Barreiro ML, Tena-Sempere M. Ghrelin and reproduction: a novel signal linking energy status and fertility? Mol Cell Endocrinol (2004) 226:1–9.[CrossRef][Web of Science][Medline]
Callahan HS, Cummings DE, Pepe MS, Breen PA, Matthys CC, Weigle DS. Postprandial suppression of plasma ghrelin level is proportional to ingested caloric load but does not predict intermeal interval in humans. J Clin Endocrinol Metab (2004) 89:1319–1324.
Caminos JE, Tena-Sempere M, Gaytan F, Sanchez-Criado JE, Barreiro ML, Nogueiras R, Casanueva FF, Aguilar E, Diéguez C. Expression of ghrelin in the cyclic and pregnant rat ovary. Endocrinology (2003) 144:1594–1602.
Cummings DE, Purnell JQ, Frayo RS, Schmidova K, Wisse BE, Weigle DS. A pre-prandial rise in plasma ghrelin levels suggests a role in meal initiation in humans. Diabetes (2001) 50:1714–1719.
Escudero E, Bosch E, Crespo J, Simon C, Remohi J, Pellicer A. Comparison of two different starting multiple dose gonadotropin-releasing hormone antagonist protocols in a selected group of in vitro fertilization-embryo transfer patients. Fertil Steril (2004) 81:562–566.[CrossRef][Web of Science][Medline]
Fasouliotis SJ, Spandorfer SD, Witkin SS, Schattman G, Liu HC, Roberts JE, Rosenwaks Z. Maternal serum levels of interferon- and interleukin-2 soluble receptor- predict the outcome of early IVF pregnancies. Hum Reprod (2004) 19:1357–1363.
Fuglsang J, Skjaerbaek C, Espelund U, Frystyk J, Fisker S, Flyvbjerg A, Ovesen P. Ghrelin and its relationship to growth hormones during normal pregnancy. Clin Endocrinol (2005) 62:554–559.[CrossRef][Medline]
Gualillo O, Caminos J, Blanco M, García-Caballero T, Kojima M, Kangawa K, Diéguez C, Casanueva F. Ghrelin, a novel placental-derived hormone. Endocrinology (2001) 142:788–794.
Hauzman E, Fedorcsák MD, Klinga K, Papp Z, Rabe T, Strowitzki T, Urbancsek J. Use of serum Inhibin A and human chorionic gonadotropin measurements to predict the outcome of in vitro fertilization pregnancies. Fertil Steril (2004) 81:66–72.[CrossRef][Web of Science][Medline]
Ioannidis G, Sacks G, Reddy N, Seyani L, Margara R, Lavery S, Trew G. Day 14 maternal serum progesterone levels predict pregnancy outcome in IVF/ICSI treatment cycles: a prospective study. Hum Reprod (2005) 20:741–746.
Kojima M, Hosoda H, Date Y, Nakazato M, Matsuo H, Kangawa K. Ghrelin is a growth-hormone-releasing acylated peptide from stomach. Nature (1999) 402:656–660.[CrossRef][Medline]
Korbonits M, Goldstone AP, Gueorguiev M, Grossman AB. Ghrelin—a hormone with multiple functions. Front Neuroendocrinol (2004) 25:27–68.[CrossRef][Web of Science][Medline]
Makino Y, Hosoda H, Shibata K, Makino I, Kojima M, Kangawa K, Kawarabayashi T. Alteration of plasma ghrelin levels associated with the blood pressure in pregnancy. Hypertension (2002) 39:781–784.
Melo MA, Meseguer M, Garrido N, Bosch E, Pellicer A, Remohi J. The significance of premature luteinization in an oocyte-donation programme. Hum Reprod (2006) 21:1503–1507.
Mueller MD, Raio L, Spoerri S, Ghezzi F, Dreher E, Bersinger NA. Novel placental and nonplacental serum markers in ectopic versus normal intrauterine pregnancy. Fertil Steril (2004) 81:1106–1111.[CrossRef][Web of Science][Medline]
Petraglia F, Santuz M, Florio P, Simoncini T, Luisi S, Plaino L, Genazzani AR, Genazzani AD, Volpe A. Paracrine regulation of human placenta: control of hormonogenesis. J Reprod Immunol (1998) 39:221–233.[CrossRef][Web of Science][Medline]
Soares SR, Troncoso C, Bosch E, Serra V, Simon C, Remohi J, Pellicer A. Age and uterine receptiveness: predicting the outcome of oocyte donation cycles. J Clin Endocrinol Metab (2005) 90:4399–4404.
Shibata K, Hosoda H, Kojima M, Kangawa K, Makino Y, Makino I, Kawarabayashi T, Futagami K, Gomita Y. Regulation of ghrelin secretion during pregnancy and lactation in the rat: possible involvement of the hypothalamus. Peptides (2004) 25:279–287.[CrossRef][Web of Science][Medline]
Tanaka K, Minoura H, Isobe T, Yonaha H, Kawato H, Wang DF, Yoshida T, Kojima M, Kangawa K, Toyoda N. Ghrelin is involved in the decidualization of human endometrial stromal cells. J Clin Endocrinol Metab (2003) 88:2335–2340.
Tena-Sempere M. Exploring the role of ghrelin as novel regulator of gonadal function. Growth Horm IGF Res (2005) 15:83–88.[CrossRef][Web of Science][Medline]
Urbancsek J, Hauzman EE, Lagarde AR, Osztovits J, Papp Z, Strowitzki T. Serum CA-125 levels in the second week after embryo transfer predict clinical pregnancy. Fertil Steril (2005) 83:1414–1421.[CrossRef][Web of Science][Medline]
Van der Lely AJ, Tschöp M, Heiman ML, Ghigo E. Biological, physiological, pathophysiological, and pharmacological aspects of ghrelin. Endocr Rev (2004) 25:426–457.
Van Voorhis BJ. Clinical practice. In vitro fertilization. N Engl J Med (2007) 356:379–386.
Zigman JM, Elmquist JK. Mini review: from anorexia to obesity—the yin and yang of body weight control. Endocrinology (2003) 144:3749–3756.
Submitted on May 10, 2007; resubmitted on December 15, 2007; accepted on December 31, 2007.
CiteULike 
Connotea 
Del.icio.us What's this?
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||