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BACKGROUND: Perfusion of the isolated uterus has been shown to be a feasible experimental system for studies of the human endometrium and myometrium. Utilizing our established experimental perfusion model we perfused 20 uteri for 27 h and investigated the contractile reactivity of the myometrium in response to 17β-estradiol (E2) and oxytocin (OT). METHODS: Uteri of group A (n = 4) were stimulated with OT; group B (n = 4) was treated continuously with E2; group C (n = 4) received both E2 and OT for 27 h; group D (n = 4) was perfused for 27 h with E2 with the addition of OT for the last 3 h of the experiment; group E (n = 4) as control group remained without any treatment. The pressure and duration of uterine contractions were recorded during the entire perfusion period using intramural and endoluminal pressure catheters. RESULTS: Compared to the other treatment groups and controls, the most effective myometrial activity was achieved in group D during the OT stimulation period. No relevant myometrial activity was detected in the control group. CONCLUSIONS: Continuous E2 treatment, with the addition of OT for the last 3 h of the 27 h perfusion period, led to the most pronounced uterotonic effects in the presented experimental condition. [ABSTRACT FROM AUTHOR]

Study Question: How do anti-Müllerian hormone (AMH) serum concentrations and follicle densities (FDs) change with age and disease and what are the implications for fertility preservation?, Summary Answer: AMH concentrations and FD do not correlate in young women, and AMH but not FD is reduced in some diseases, limiting the value of AMH as a predictive parameter of ovarian tissue transplantation., What Is Known Already: AMH is widely used as a parameter to estimate the ovarian reserve. However, the reliability of AMH to predict total number of follicles and the FD is questionable. Women with lymphoma and leukaemia have been shown to have reduced AMH concentrations, but it is unknown if the FD is also reduced. In fertility preservation it is essential to estimate the correct total number of follicles and the FD, as ovarian tissue should only be cryopreserved if ovarian reserve is high. Furthermore, the amount of tissue to be transplanted should be based on the estimation of the real FD., Study Design, Size, Duration: This retrospective observational study included 830 women (mean ± SD age, 28.2 ± 6.81 years; range, 4-43 years) with malignant (n = 806) and benign (n = 24) diseases who cryopreserved tissue in a single centre as part of a national fertility preservation programme. Females with ovarian surgery or known predispositions for a reduced ovarian reserve were excluded. AMH concentrations and FD were evaluated from March 2011 to September 2016., Participants/materials, Setting, Methods: AMH concentrations were analysed before gonadotoxic therapies. Standardized biopsies, obtained from different areas of ovarian cortex, were collected. FD was analysed after tissue digestion and calcein staining and was expressed as average number of primordial and primary follicles count per 3 mm biopsy and per cubic millimeter tissue. AMH concentrations and FD were analysed in relation to age and diagnosis group. Both parameters were age adjusted, and associations between the different diagnosis groups and AMH versus FD were assessed., Main Results and the Role of Chance: Mean ± SD AMH concentration was 3.1 ± 2.81 g/ml, mean FD per 3 mm biopsy was 137 ± 173.9 and 19.4 ± 24.60 per mm3. Maximum AMH concentrations were found in children and teenagers at the age of 6-10 years (5.71 ng/ml) and in adults at the age of 21-25 years (3.33 ng/ml). FD was highest in young children up to an age of 15 years and decreased with increasing age. AMH and FD were not correlated in women ≤20 years and weakly to moderately correlated in women 21-40 years (r = 0.24-0.39). Age-adjusted correlations between AMH and FD were demonstrated in several diagnosis groups such as breast cancer, leukaemia, sarcoma, gastrointestinal cancer and gynaecological cancer but not in the groups exhibiting Hodgkin's and non-Hodgkin's lymphoma, cerebral cancer, other types of malignancies and other types of benign diseases. Further statistical analysis supported the finding that, in some diagnosis groups such as Hodgkin's lymphoma and in gynaecological cancer, AMH concentrations but not FDs are reduced, questioning the prognostic accuracy of AMH for the FD in these diseases., Limitations, Reasons for Caution: Even though biopsies were taken from different sites, heterogenous distribution of follicles might have had some effect on the accuracy of the analysis., Wider Implication of the Findings: AMH should be used with care to estimate the total ovarian reserve and FD of cancer patients in young women in some diseases. Therefore, calculating the amount of ovarian tissue to be transplanted based solely on AMH might be inaccurate whereas FD might be a better parameter., Study Funding/competing Interest(s): The study did not receive any exterior funding., (© The Author(s) 2019. Published by Oxford University Press on behalf of the European Society of Human Reproduction and Embryology. All rights reserved. For permissions, please e-mail: journals.permission@oup.com.)

Research Question: Is overnight transportation of ovarian tissue before cryopreservation in a centralized cryobank from the FertiPROTEKT network feasible?, Design: Data from 1810 women with cryopreserved ovarian tissue after overnight transportation from December 2000 to December 2017 were analysed with a focus on transportation, tissue activity parameters and pregnancy, and delivery rates after transplantation., Results: A total of 92.4% of tissue samples arrived at ideal temperatures of 2-8°C, 0.4% were transported at temperatures lower than ideal and 6.4% were transported at temperatures that were too high, generally due to mishandling of the inlayed cool packs of the transportation boxes. In 62 women, 78 tissue transplantations were carried out. A subgroup of 30 women who underwent a single orthotopic transplantation with fulfilled criteria of a complete follow-up after transplantation until the end of study, a premature ovarian insufficiency after gonadotoxic therapy as well as the absence of pelvic radiation, was further analysed. In this group, transplantations into a peritoneal pocket accounted for 90%. Transplants were still active at 1 year and above after transplantation in 93.3%. Pregnancy and delivery rates were 46.7% and 43.3%, respectively, with one ongoing pregnancy at the end of the study., Conclusions: Overnight transportation for central cryobanking is a feasible concept that results in high reproducible success rates through standardized professional tissue freezing and storage., (Copyright © 2019. Published by Elsevier Ltd.)

The cryopreservation of ovarian tissue with subsequent transplantation of the tissue represents an established method of fertility protection for female patients who have to undergo gonadotoxic therapy. The procedure can be performed at any point in the cycle and thus generally does not lead to any delay in oncological therapy. With the aid of this procedure, more than 130 births to date worldwide have been able to be recorded. The birth rate is currently approximately 30% and it can be assumed that this will increase through the further optimisation of the cryopreservation and surgical technique. The concept paper presented here is intended to provide guidance for managing cryopreservation and transplantation of ovarian tissue to German-speaking reproductive medicine centres.

Background: While changes in the composition of breast milk throughout the lactation period are well known, little is known about the antioxidative capacity of breast milk and its regulation as a function of time of day., Objective: The aim of this study was to evaluate the antioxidative capacity in breast milk and its regulation by time of day., Methods: Melatonin, superoxide dismutase (SOD), glutathione peroxidase 3 (Gpx3) concentrations, and the total antioxidative capacity (TAOC) were analyzed in 105 breast milk samples and 12 maternal serum samples from 21 healthy nursing mothers., Results: Comparison between daytime breast milk (collected from 1000-2200 h) and nighttime breast milk (collected from 2200-1000 h) revealed significantly higher concentrations of melatonin and Gpx3 in nighttime milk (melatonin: 1.5 pg/mL [1.0-2.1] day vs 7.3 pg/mL [3.8-13.6] night, median [quartiles], with an estimated mean night-to-day ratio of 5.2 [3.9, 7.1], P < .001; Gpx3: 1436 ng/mL [765-2060] day vs 1800 ng/mL [1242-2297] night, night-to-day difference 192.1 [0.6, 383.7], P = .049). Subgroup analysis showed that melatonin had a circadian rhythm in both preterm and term milk, with a significantly higher nighttime concentration ( P < .001), while antioxidant enzymes had a circadian rhythm only in preterm milk, with a significantly higher nighttime concentration for Gpx3 and a significant higher daytime concentration for SOD and TAOC ( P = .041 and P = .049, respectively). We found no significant correlation between the concentration of melatonin and the concentration of SOD, Gpx3, or TAOC. Moreover, there were no significant correlations observed between gestational age and the concentration of melatonin and antioxidant enzymes., Conclusion: Because of its higher melatonin and Gpx3 content, future research is needed to determine if preterm nighttime milk ought to be the first choice in the feeding of high-risk preterm infants.

Background: There are important physiological changes in the maternal, placental, and fetal compartments during pregnancy and labor. Increased oxidative stress has been demonstrated during labor. Melatonin has been reported to serve as an indirect antioxidant via the stimulation and induction of antioxidant enzymes as superoxide dismutase (SOD) and glutathione peroxidase (Gpx) in several tissues., Aim: : To assess whether the melatonin status, presence of labor at the time of birth and the time of delivery influence the extracellular antioxidative enzymes and DNA oxidative stress in newborns., Methods: The extracellular antioxidative status and oxidative stress were analyzed by measuring the concentrations of the SOD3, Gpx3 and 8-hydroxydeoxyguanosine (8-OHdG) in the cord blood of 135 newborns. Newborns delivered during the day and at night and newborns delivered by spontaneous vaginal delivery (labor group) or elective caesarean section delivery (no labor group) were studied., Outcome Measures: The concentration of melatonin, SOD3, Gpx3 and 8-OHdG., Results: Independent of the time of delivery, we found significantly higher melatonin, SOD3 and Gpx3 but lower 8-OHdG concentrations in the labor group than in the no labor group. We did not observe a correlation between the concentration of melatonin and SOD3, Gpx3 or 8-OHdG, or a day-night difference in SOD3, Gpx3 or 8-OHdG., Conclusion: Our findings suggest that oxidative stress during labor leads to an elevation of melatonin, SOD3 and Gpx3 in the fetal circulation, protecting the newborn from serious impairment, which is reflected by lower 8-OHdG levels. The melatonin status at the time of birth does not influence the extracellular SOD3 or Gpx3 concentrations., (Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.)

Objective: To investigate the effects of a dynamic fluidic culture system on early in vitro folliculogenesis in standardized ovarian cortex biopsies., Design: Cortical small strips were cultured for 6 days in a conventional static or in a dynamic fluidic culture system., Setting: University-affiliated laboratory with an associated cryobank facility., Patient(s): Ovarian cortex from postpuberal female cancer patients (26.1 ± 1.3 y) who opted for cryopreservation of their tissue for fertility protection before gonadotoxic cancer therapy. With informed consent of the Institutional Ethics Committee, part of the tissue was available for patient-related research studies., Intervention(s): None., Main Outcome Measure(s): The viability and proliferative capacity of the cortex biopsies were evaluated by chemiluminescent microparticle immunoassay for detection of in vitro produced E2 and P in the supernate, by viable follicle counting via calcein staining, by histologic analyses, and by total RNA preparation and reverse transcription for real-time polymerase chain reaction of selected early folliculogenesis genes., Result(s): The data support the notion that early follicle development can be better achieved in vitro in a dynamic fluidic culture system. The findings are based on the presence of more viable follicles, higher expression levels of early folliculogenesis genes KIT-L, INHB, and GDF9, and the absence of premature luteinization of follicles., Conclusion(s): This study provides evidence that dynamic fluidic culture is a promising approach for investigating early follicular recruitment and growth in cortical biopsies. It may serve as a first step in a multistep culture system to design a complex in vitro system for complete folliculogenesis., (Copyright © 2013 American Society for Reproductive Medicine. Published by Elsevier Inc. All rights reserved.)

Objective: Nuchal translucency (NT) measurement in assisted reproduction treatment (ART) twins is less extensively investigated. Therefore, the present study compared NT measurements of spontaneously conceived twins with ART twins in dichorionic (DC) and monochorionic (MC) pregnancies., Methods: Retrospective analysis of 706 unaffected twins between 11 + 0 and 13 + 6 weeks conceived either spontaneously (n = 362) or with ART (n = 344). The group with spontaneous conception included 234 DC (64.6%) and 128 MC (35.4%) pregnancies. In the ART group, 326 were DC (94.7%) and 18 were MC (5.3%). NT values were transformed into multiples of median (MoM)., Results: In the DC group, no significant differences between ART and spontaneously conceived twins (NT MoM 1.06 ± 0.28 vs 1.03 ± 0.29; p > 0.05) were observed. NT MoM of MC ART twins was higher compared with spontaneous MC twins (1.23 ± 0.82 vs 0.99 ± 0.27; p = 0.011). Although the incidence of twin-to-twin transfusion syndrome (TTTS) was higher among ART twins (11.1% vs 4.7%), inter-twin NT difference was similar between pregnancies with TTTS (0.42 ± 0.21) or without (0.40 ± 0.71)., Conclusions: Measurement of NT thickness in DC ART twins achieves comparable results with twins conceived spontaneously. Conclusions in MC twins are limited; however, higher NT MoM was not related to TTTS or selective intrauterine growth restriction., (© 2013 John Wiley & Sons, Ltd.)

Background and Aims: Melatonin (MT) is rapidly transferred from the maternal to fetal circulation in humans. There is little knowledge about factors which influence the MT concentration (MTc) in the umbilical cord (UC) blood during delivery. The aim of our study was to evaluate the MT status in the UC blood according to the time and mode of delivery., Subjects and Methods: Blood samples from umbilical artery (UA) and vein (UV) were collected from spontaneous vaginal deliveries (SVD, n=122) and cesarean section deliveries (CSD, n=188). MTc was measured using a commercially available radioimmunoassay., Results: The MTc was not significantly different between UA and UV blood both at daytime and at nighttime (p=0.216 and p=0.440, respectively). Both in UA and in UV, the MTc was significantly higher at nighttime than at daytime (p<0.0001). Compared with the CSD group, MTc in the SVD group was significantly higher both at night- and daytime (p<0.05). MTc both in UA and in UV was found to be not significantly different between patients with and without risk factors for stress including pregnancy complications (e.g., preeclampsia) and intrapartum complications (e.g., emergency section, pathological doppler, and pathological cardiotocography) (p>0.05)., Conclusion: Our study revealed for the first time that MTc both in UA and in UV depends on modus of labor. In agreement with other studies, we found a clear circadian MT rhythm in the UC blood of neonates. The results of our study may suggest to a physiological role of MT at the onset of labor., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Objective: Considering the potential immunomodulatory role of melatonin and its direct antioxidant activity, disturbances of the melatonin secretion pattern in the septic conditions could be particularly unfavorable. The aim of this study was to evaluate the nocturnal melatonin concentration and total 24-hr excretion of 6-sulfatoxymelatoninsulfate, melatonin's major urinary metabolite, in children with sepsis in the pediatric intensive care unit., Design: Prospective observational pilot study., Setting: A pediatric intensive care unit., Patients: Twenty septic and 20 nonseptic children admitted between February 2008 and January 2010., Interventions: None., Measurement and Main Results: Blood and urine samples were obtained from each patient on days 1, 2, 3, 5, and 10. There were no significant differences between the groups concerning age and gender. The median nocturnal melatonin concentrations were not significantly different between septic and nonseptic patients during the study period (p > .05). A subgroup analysis in septic patients showed that the nocturnal melatonin concentrations in nonsurvivors were significantly higher than in survivors, whereas total 6-sulfatoxymelatoninsulfate excretions in nonsurvivors were significantly lower than in survivors (p = .001 and p = .015, respectively). Furthermore, nocturnal melatonin concentrations of septic patients in septic shock state were statistically significantly higher than those of septic patients without septic shock state (p = .002). The 24-hr 6-sulfatoxymelatoninsulfate excretions in septic patients with liver dysfunction were found significantly lower than those in septic patients without liver dysfunction (p = .015). The presence of sedation and mechanical ventilation had no effect on the nocturnal melatonin concentrations in septic patients (p = .953 and p = .922, respectively)., Conclusion: The present study shows that, in contradiction to results in adult patients, the nocturnal melatonin concentrations are not decreased in septic pediatric intensive care unit patients despite severe disease. Further investigations are needed to identify whether treatment with melatonin may have beneficial effects in pediatric intensive care unit patients with sepsis/septic shock.

Previously, we reported on inter-individual and gender specific variations of LINE-1 methylation in healthy individuals. In this study, we investigated whether this variability could be influenced by age or sex hormones in humans. To this end, we studied LINE-1 methylation in vivo in blood-derived DNA from individuals aged 18 to 64 years and from young healthy females at various hormone levels during the menstrual cycle. Our results show that no significant association with age was observed. However, the previously reported increase of LINE-1 methylation in males was reconfirmed. In females, although no correlation between LINE-1 or Alu methylation and hormone levels was observed, a significant stable individual specific level of methylation was noted. In vitro results largely confirmed these findings, as neither estrogen nor dihydrotestosterone affected LINE-1 or Alu methylation in Hek293T, HUVEC, or MDA-kb2 cell lines. In contrast, a decrease in methylation was observed in estrogen-treated T47-Kbluc cell lines strongly expressing estrogen receptor. The very low expression of estrogen receptor in blood cells could explain the observed insensitivity of methylation at LINE-1 to natural hormonal variations in females. In conclusion, neither natural cycle of hormones nor age has a detectable effect on the LINE-1 methylation in peripheral blood cells, while gender remains an important factor.

The aim of this study was to evaluate whether nocturnal melatonin concentration (NMC) and urinary 6-sulphatoxymelatonin (aMT6s) excretion can predict melatonin status in patients with severe sepsis in the pediatric intensive care unit (PICU). Blood samples for the determination of NMC were obtained from each patient at 3 a.m. Urine samples for the determination of aMT6s excretion were obtained from each patient at 12 h intervals. We obtained 89 blood and 178 urine samples from 23 septic patients, and 52 blood and 104 urine samples from 13 non-septic patients. The NMC of septic patients in a state of septic shock was significantly higher than that of septic patients not in septic shock (p = 0.017) and those of non-septic patients (p = 0.019). In contrast, there was no significant difference for nocturnal (NaMT6s) and total aMT6s (TaMT6s) excretion between septic patients with and without septic shock and non-septic patients (p > 0.05). The NMC was significantly higher in septic patients in shock with and without hepatic dysfunction (HD) than in non-septic patients (p = 0.004 and p = 0.024, respectively). NaMT6s and TaMT6s excretion was significantly lower in septic patients with HD than in septic patient without HD (p = 0.040 and p = 0.029, for NaMT6s and TaMT6s, respectively). Our results showed that an elevated NMC may not reflect an increased MT production in septic patients in septic shock. It seems that, to evaluate the melatonin status of septic PICU patients, it is necessary to collect both serum and urine samples.

Subjects: The aim of this study was to assess whether salivary melatonin could be used as a reliable alternative to serum melatonin to study the pineal physiology in newborn infants., Design and Methods: The 95 newborn infants were allocated to four groups according to the time of sampling (09-11am, 03-05pm, 09-11pm, and 03-05am)., Results: The median melatonin levels in serum and saliva were not significantly different between groups: median (interquartile range), 18.4pg/mL (13.9-26.0pg/mL) and 10.6pg/mL (7.5-14.9pg/mL); 13.3pg/mL (11.5-19.0pg/mL) and 9.1pg/mL (7.8-14.2pg/mL); 16.0pg/mL (12.4-18.7pg/mL) and 12.3pg/mL (8.2-16.8pg/mL); 13.0pg/mL (8.8-27.4pg/mL) and 11.2pg/mL (7.7-16.6pg/mL) for groups 1, 2, 3, and 4, respectively (p>0.05). The results revealed a highly significant correlation between the serum and salivary melatonin levels (Pearson's correlation coefficient, r=0.763; P<0.001)., Conclusion: Melatonin levels in saliva reflect those in serum at any time of the day and like serum melatonin levels do not increase at night., (Copyright 2010 The Canadian Society of Clinical Chemists. Published by Elsevier Inc. All rights reserved.)

First-trimester serum markers in 110 in-vitro fertilization (IVF) and 331 intracytoplasmatic sperm injection (ICSI) pregnancies were compared with 1431 pregnancies with spontaneous conception. Alterations of serum markers were evaluated with respect to small-for-gestational-age (SGA) growth and number of embryos transferred. For pregnancy-associated plasma protein A (PAPP-A), significantly lower concentrations were observed in IVF and ICSI pregnancies compared with controls (0.86 and 0.9 versus 1.06; P<0.001). Free beta-human chorionic gonadotrophin (betaHCG) values were significantly higher in the IVF/ICSI groups than in controls (1.1 and 1.1 versus 0.94; P<0.005). IVF and ICSI pregnancies showed higher rates of SGA (10.0% and 8.2%) compared with natural conception (4.6%), but differences in PAPP-A concentrations remained significant (P<0.005) after the exclusion of SGA pregnancies. No relationship between serum values and the transfer of one, two or three embryos was observed. Centre-specific corrections may be needed to adjust screening parameters for assisted reproductive technology., (Copyright (c) 2009 Reproductive Healthcare Ltd. Published by Elsevier Ltd. All rights reserved.)

Background and Aims: Pineal physiology is not completely elucidated in newborn infants. As melatonin in pharmacological doses has been reported to reduce oxidative stress in neonates with asphyxia, respiratory distress syndrome, or sepsis, there is the need to better understand the physiological role of melatonin in the neonatal period. The aim of this study was to evaluate a new saliva sampling method suitable for newborn infants and to assess whether salivary melatonin could be used as a reliable, non-invasive, pain-free alternative to serum melatonin to study the pineal physiology in newborn infants., Subjects and Methods: In 86 healthy term newborn infants, a serum sample was collected by venipuncture after 36h of life during blood sampling for newborn screening, immediately after a saliva sample had been collected., Results: Of the 86 saliva samples, 62 were 'ideal' samples for the analysis. The median serum and salivary melatonin levels of the 62 newborns were 14.4pg/mL (11.5-20.5pg/mL) and 10.8pg/mL (7.5-16.1pg/mL), respectively. There was no significant difference between serum and salivary melatonin levels. The results revealed a highly significant correlation between the serum and salivary melatonin levels (Pearson's correlation coefficient, r=0.793; p<0.001). Linear regression analysis showed that the equation for the relationship between serum (x) and saliva (y) was y=1.12x-5.58pg/mL., Conclusion: To study pineal function in newborn infants, saliva collection using cotton buds and measurement of melatonin in saliva offers a valid, non-invasive, pain-free and practical alternative to blood sampling and determination of serum melatonin.

The phthalate ester mono-(2-ethylhexyl) phthalate (MEHP) is the active metabolite of di-(2-ethylhexyl) phthalate, a high-production-volume chemical used as a plasticizer and solvent in numerous consumer products. MEHP has been demonstrated to be a reproductive toxicant in rodents decreasing estradiol and progesterone production in preovulatory granulosa cells. In the present study, we examined the effect of MEHP on steroid production of human granulosa-lutein (GL) cells. Human GL cells collected from women undergoing in vitro fertilization were cultured in medium containing FSH, hCG and 8-Br-cAMP, respectively, together with various concentrations of MEHP (0-500 micromol L(-1)). After incubation for 48 h estradiol and progesterone were assayed in the spent culture medium. Furthermore, aromatase activity and mRNA levels of GL cells were determined. Basal as well as FSH-, hCG- and 8-Br-cAMP-stimulated estradiol production of GL cells was suppressed by MEHP in a dose-dependent manner (IC(50)=105 micromol L(-1), 138 micromol L(-1), 49 micromol L(-1) and 78 micromol L(-1)). Furthermore aromatase activity and mRNA levels were reduced in GL cells cultured with MEHP. In contrast, MEHP did not alter the production of progesterone up to a concentration of 167 micromol L(-1). The present data indicate that MEHP is a specific inhibitor of estradiol production in human GL cells with a post-cAMP site of action. The inhibition of estradiol production obviously results from a reduction of aromatase activity on the transcript level. As the in vitro effective doses of MEHP are within the range of real environmental exposure levels an inhibitory effect on estrogen production in vivo seems to be possible.

Background: Because of the vast range of physiological relevant estradiol concentrations the requirements to be met by an estradiol assay are high. In the present study the performance of various commercially available estradiol assays was evaluated with regard to imprecision and long-term stability., Methods: Precision and long-term stability of 7 commercially available estradiol immunoassays were assessed in a multi-centre quality control study based on the repeated measurement of liquid BIOREF estradiol control sera by 18 laboratories during a 14-month study period., Results: The mean estradiol concentrations determined in 594 runs performed for each control level were 71 pg/ml, 349 pg/ml and 676 pg/ml. A high variation was found for the method specific mean values calculated from all results measured with the same method, which ranged between 32 - 90 pg/ml, 187 - 392 pg/ml and 373 - 790 pg/ml, resulting in a similar high inter-laboratory variation with coefficients of variation (CVs) of 25.0%, 16.7% and 17.5%. In contrast, the intra-laboratory variation of estradiol values as well as the variation of values measured with the same method were found to be considerably lower with coefficients of variation < 10% for most laboratories and methods; only the low control level was measured with CV values > 10% by the majority of laboratories and methods. For none of the laboratories a tendency was observed in the results from beginning to end of the 14 month study period indicating a high uniformity in assay production and a good long-term stability of the control material used., Conclusions: The present data demonstrate that also with the currently available estradiol immunoassays the comparability of results measured with different methods is limited. With most assays very low estradiol concentrations, as observed in postmenopausal women, can be determined only with a precision which is not adequate for clinical assessment.