Breeding season and ovulation rate in ewes treated with long days in spring followed by a melatonin implant and exposure to a ram

1996 ◽  
Vol 62 (3) ◽  
pp. 507-512 ◽  
Author(s):  
T. Sweeney ◽  
D. O'Callaghan
Keyword(s):  
Breeding Season ◽  
Luteal Phase ◽  
Signal Sequence ◽  
Ovulation Rate ◽  
Continuous Exposure ◽  
Biphasic Response ◽  
Reproductive State ◽  
Serum Progesterone ◽  
Natural Photoperiod ◽  
Median Date

AbstractWhile the onset of the breeding season in ewes can be advanced up to 7 weeks following exposure to long days (44 days) before lambing, a melatonin implant from lambing and exposure to a ram from the summer solstice, this advance is reduced by the absence of a ram. The aim of this experiment was to determine if earlier exposure to the ram and/or exposure to more long days before lambing would further advance the onset of the breeding season. A further aim was to compare the ovulation rate and duration of the breeding season between ewes with a normal and advanced onset of the breeding season due to this treatment regime. Pregnant ewes lambing in mid March were allocated to treatments as follows: (1) controls, maintained on natural photoperiod; (2) 44 LD + mel, exposed to 44 long days (18L: 6D; LD) before lambing followed by a 700-mg melatonin implant after lambing; (3) 90 LD + mel, as in treatment 2, but exposed to 90 LD before lambing; (4) 90 LD + mel + ram, as in treatment 3, including continuous exposure to a vasectomized ram from 10 April. Reproductive state was assessed from serum progesterone concentrations in blood collected at 3- to 4-day intervals from 10 April and ovulation rate was determined during the luteal phase of the first five oestrous cycles in control ewes and ewes exposed to 90 LD + mel + ram. Ewes exposed to 90 LD + mel + ram commenced the breeding season 10 weeks earlier (median date 25 July, range 28 days;P< 0·001) than controls (median date 8 October, range 68 days). Overall, the onset of the breeding season was not advanced in ewes given 44 or 90 LD + mel in the absence of a ram, but a biphasic response was evident, with 40 to 50% of ewes beginning the breeding season at the same time as ewes on 90 LD + mel + ram. Ovulation rate was similar between control ewes and ewes exposed to 90 LD + mel + ram (P > 0·05). The duration of the breeding season was longer in ewes exposed to 90 LD + mel + ram (210 (s.e. 15) days;P< 0·002) than in control ewes (158 (s.e. 10) days), with no difference in date of the end of the breeding season (P > 0·05). Exposure of ewes to 90 LD before lambing in March, followed by a melatonin implant and exposure to the ram from 10 April advanced the onset and extended the duration of the breeding season without an overall effect on ovulation rate. The ram is an important component of this signal sequence.

Effects of immunization against recombinant bovine inhibin α subunit on circulating concentrations of gonadotrophins in ewes

1989 ◽  
Vol 120 (1) ◽  
pp. 59-65 ◽  
Author(s):  
J. K. Findlay ◽  
B. Doughton ◽  
D. M. Robertson ◽  
R. G. Forage
Keyword(s):  
Breeding Season ◽  
Untreated Control ◽  
Luteal Phase ◽  
Plasma Concentrations ◽  
Follicular Phase ◽  
Ovulation Rate ◽  
Α Subunit ◽  
Keyhole Limpet Haemocyanin ◽  
Fourfold Increase ◽  
Breeding Seasons

ABSTRACT Immunization of ewes against a pure recombinant preparation of the α subunit of bovine inhibin (α-bI) resulted in a three- to fourfold increase in ovulation rate, associated with antibodies in plasma recognizing pure native 31 kDa inhibin. The aim of this study was to examine the effects of this immunization on basal and GnRH-stimulated plasma concentrations of FSH and LH in ewes during the anoestrous and breeding seasons. The groups were untreated control ewes (n = 5), control ewes treated with keyhole limpet haemocyanin (KLH alone, n = 4), ewes treated with α-bI alone (n = 4) and α-bI–KLH conjugate-treated ewes (n = 3). There were no effects of immunization on basal FSH or LH in anoestrous ewes, despite the presence of antibodies recognizing 31 kDa inhibin. In the breeding season, immunization against α-bI resulted in increased basal (follicular phase, P < 0·1; luteal phase P < 0·05) and GnRH-stimulated (follicular phase only, P < 0·001) release of FSH, but not LH. The data are compatible with the hypotheses that the increase in ovulation rate in immunized ewes is due to an increase in circulating FSH concentrations and that inhibin may only have a major peripheral influence on FSH in sheep during the breeding season. Journal of Endocrinology (1989) 120, 59–65

Effect of previous lambing date and subsequent month of mating on reproductive performance in Mule ewes

1999 ◽  
Vol 69 (1) ◽  
pp. 217-222 ◽  
Author(s):  
L. M. Mitchell ◽  
M. E. King ◽  
R. P. Aitken ◽  
J. M. Wallace
Keyword(s):  
Factorial Design ◽  
Breeding Season ◽  
Reproductive Performance ◽  
Ovulation Rate ◽  
Corpora Lutea ◽  
Fertilization Failure ◽  
Mating Period ◽  
Natural Photoperiod ◽  
Natural Breeding ◽  
Main Factor

AbstractThe objective was to determine the effect of previous lambing date and subsequent month of mating on reproductive performance in Mule (Bluefaced Leicester × Scottish Blackface) ewes. Sixty-four ewes which had previously lambed in January (13 January (s.e. = 1 day)) and 80 ewes which had previously lambed in May (15 May (s.e. = 1 day)) were allocated equally to four mating periods (30 August to 17 September, 1 November to 19 November, 3 January to 21 January and 14 February to 4 March) in a 2 × 4 factorial design. From 20 days before and during their designated mating period, January- and May-lambing ewes were separately housed in straw-bedded pens under natural photoperiod and were given 1 kg per head per day dried grass pellets. A vasectomized ram was continuously present with each group for 17 days and was replaced by a raddled, fertility tested entire Suffolk ram at the start of the mating period. Ewes were mated at a single natural oestrus and those marked by the ram were recorded daily. Ovulation rate was measured by laparoscopy on day 6 after mating. For ewes which had previously lambed in January (16 per group), numbers by month of mating that showed oestrous behaviour, ovulated and were pregnant, respectively, were: September, 16, 15 and 12; November, 16, 15 and 14; January, 15, 15 and 10 and February, 15, 16 and 7. Mean (s.e.) ovulation rates by month of mating were 2·1 (0.16), 2·5 (0.19), 2·1 (0.09) and 2·2 (0.19) corpora lutea per ewe ovulating, and lambing rates by month of mating were 1·3 (0.25), 1·9 (0.25), 1·2 (0.24) and 0·8 (0.23) lambs per ewe to the ram. For ewes which had previously lambed in May (20 per group), numbers by month of mating that showed oestrous behaviour, ovulated and were pregnant, respectively, were: September, 13, 20 and 12; November, 20, 20 and 19; January, 20, 20 and 17 and February, 20, 20 and 13. Mean (s.e.) ovulation rates by month of mating were 2·0 (0.13), 2·3 (0.11), 2·1 (0.05) and 2·2 (0.11) corpora lutea per ewe ovulating, and lambing rates by month of mating were 1·0 (0.21), 2·1 (0.15), 1·5 (0.17) and 1·2 (0.21) lambs per ewe to the ram. Ovulation, pregnancy and lambing rates were not influenced by previous lambing date, but lambing rates were significantly (P < 0·01) reduced for ewes mated in September and February compared with November. Results demonstrate that in Mule ewes acceptable ovulation rates can be achieved throughout the period September to February but lambing rates are reduced when ewes are mated at the extremes of their natural breeding season. The main factor contributing to the reduction in lambing rates was an increase in the number of ewes failing to establish pregnancy as a consequence of ovulation without oestrous behaviour, fertilization failure and (or) total embryo loss.

Individualised luteal phase support in artificially prepared frozen embryo transfer cycles based on serum progesterone levels: a prospective cohort study

2021 ◽  
Author(s):  
Manuel Álvarez ◽  
Sofía Gaggiotti-Marre ◽  
Francisca Martínez ◽  
Lluc Coll ◽  
Sandra García ◽  
...  
Keyword(s):  
Pregnancy Rate ◽  
Embryo Transfer ◽  
Pregnancy Outcomes ◽  
Luteal Phase ◽  
Frozen Embryo Transfer ◽  
Ongoing Pregnancy ◽  
Serum Progesterone ◽  
Endometrial Preparation ◽  
Group 2 ◽  
Group 1

Abstract STUDY QUESTION Does an individualised luteal phase support (iLPS), according to serum progesterone (P4) level the day prior to euploid frozen embryo transfer (FET), improve pregnancy outcomes when started on the day previous to embryo transfer? SUMMARY ANSWER Patients with low serum P4 the day prior to euploid FET can benefit from the addition of daily subcutaneous P4 injections (Psc), when started the day prior to FET, and achieve similar reproductive outcomes compared to those with initial adequate P4 levels. WHAT IS KNOWN ALREADY The ratio between FET/IVF has spectacularly increased in the last years mainly thanks to the pursuit of an ovarian hyperstimulation syndrome free clinic and the development of preimplantation genetic testing (PGT). There is currently a big concern regarding the endometrial preparation for FET, especially in relation to serum P4 levels around the time of embryo transfer. Several studies have described impaired pregnancy outcomes in those patients with low P4 levels around the time of FET, considering 10 ng/ml as one of the most accepted reference values. To date, no prospective study has been designed to compare the reproductive outcomes between patients with adequate P4 the day previous to euploid FET and those with low, but restored P4 levels on the transfer day after iLPS through daily Psc started on the day previous to FET. STUDY DESIGN, SIZE, DURATION A prospective observational study was conducted at a university-affiliated fertility centre between November 2018 and January 2020 in patients undergoing PGT for aneuploidies (PGT-A) IVF cycles and a subsequent FET under hormone replacement treatment (HRT). A total of 574 cycles (453 patients) were analysed: 348 cycles (leading to 342 euploid FET) with adequate P4 on the day previous to FET, and 226 cycles (leading to 220 euploid FET) under iLPS after low P4 on the previous day to FET, but restored P4 levels on the transfer day. PARTICIPANTS/MATERIALS, SETTING, METHODS Overall we included 574 HRT FET cycles (453 patients). Standard HRT was used for endometrial preparation. P4 levels were measured the day previous to euploid FET. P4 &gt; 10.6 ng/ml was considered as adequate and euploid FET was performed on the following day (FET Group 1). P4 &lt; 10.6 ng/ml was considered as low, iLPS was added in the form of daily Psc injections, and a new P4 analysis was performed on the following day. FET was only performed on the same day when a restored P4 &gt; 10.6 ng/ml was achieved (98.2% of cases) (FET Group 2). MAIN RESULTS AND THE ROLE OF CHANCE Patient’s demographics and cycle parameters were comparable between both euploid FET groups (FET Group 1 and FET Group 2) in terms of age, weight, oestradiol and P4 levels and number of embryos transferred. No statistically significant differences were found in terms of clinical pregnancy rate (56.4% vs 59.1%: rate difference (RD) −2.7%, 95% CI [−11.4; 6.0]), ongoing pregnancy rate (49.4% vs 53.6%: RD −4.2%, 95% CI [−13.1; 4.7]) or live birth rate (49.1% vs 52.3%: RD −3.2%, 95% CI [−12; 5.7]). No significant differences were also found according to miscarriage rate (12.4% vs 9.2%: RD 3.2%, 95% CI [−4.3; 10.7]). LIMITATIONS, REASONS FOR CAUTION Only iLPS through daily Psc was evaluated. The time for Psc injection was not stated and no serum P4 determinations were performed once the pregnancy was achieved. WIDER IMPLICATIONS OF THE FINDINGS Our study provides information regarding an ‘opportunity window’ for improved ongoing pregnancy rates and miscarriage rates through a daily Psc injection in cases of inadequate P4 levels the day previous to FET (P4 &lt; 10.6 ng/ml) and restored values the day of FET (P4 &gt; 10.6 ng/ml). Only euploid FET under HRT were considered, avoiding one of the main reasons of miscarriage and implantation failure and overcoming confounding factors such as female age, embryo quality or ovarian stimulation protocols. STUDY FUNDING/COMPETING INTEREST(S) No external funding was received. B.C. reports personal fees from MSD, Merck Serono, Ferring Pharmaceuticals, IBSA and Gedeon Richter outside the submitted work. N.P. reports grants and personal fees from MSD, Merck Serono, Ferring Pharmaceuticals, Theramex and Besins International and personal fees from IBSA and Gedeon Richter outside the submitted work. The remaining authors have no conflicts of interest to declare. TRIAL REGISTRATION NUMBER NCT03740568.

A note on attainment of puberty of september-born early-maturing ewe lambs in relation to level of nutrition

1991 ◽  
Vol 53 (3) ◽  
pp. 407-409 ◽  
Author(s):  
F. Forcada ◽  
J. A. Abecia ◽  
L. Zarazaga
Keyword(s):  
Sexual Activity ◽  
Breeding Season ◽  
Ovulation Rate ◽  
Corpora Lutea ◽  
Plasma Progesterone ◽  
Ewe Lambs ◽  
Early Maturing ◽  
Age At Puberty

The attainment of puberty in September-born early-maturing ewe lambs was studied at Zaragoza (latitude 41° 40' N). Thirty twin Salz females were allocated to two groups receiving two nutrition levels after 3 months of age: high (500 g/day lucerne hay and 500 g/day concentrate) (H) and low (500 g/ day lucerne hay) (L). Oestrus was detected daily by aproned rams. Corpora lutea were counted after oestrus and plasma progesterone levels monitored each week.In the first breeding season (January to February) the percentage of females showing sexual activity (silent emulation or oestrus and ovulation) was higher in the H compared with the L group (67 and 20%; P < 0/05). Nonpubertal oestrus before the main breeding season was detected in 67% of animals. In the main breeding season and for H and L groups respectively, percentage of females showing silent ovulation before puberty was 67 and 33% and mean age at puberty extended to 319 (s.e. 4-8) and 314 (s.e. 3·7) days. Ovulation rate at puberty was 1·73 (s.e. 0·13) and 1·33 (s.e. 0·15) respectively (P < 0·05).

scholarly journals 142 Evaluation of estrus detection patches as a tool to classify postpartum beef cows as estrous cycling or anestrous prior to the start of the breeding season

2020 ◽  
Vol 98 (Supplement_4) ◽  
pp. 116-117
Author(s):  
Emily G Smith ◽  
Rachael C Bonacker ◽  
Carson M Andersen ◽  
Jordan M Thomas
Keyword(s):  
Pregnancy Rate ◽  
Breeding Season ◽  
Beef Cows ◽  
Estrus Synchronization ◽  
Serum Progesterone ◽  
Estrus Detection ◽  
Estrous Cyclicity ◽  
Type Ii Errors ◽  
Estrous Cycling

Abstract Estrus detection patches were evaluated as a tool to classify postpartum cows as estrous cycling or anestrous at the start of the breeding season. EstrotectTM Breeding Indicators were applied to 257 postpartum beef cows in three locations 25 days prior to the start of estrus synchronization. Coincident with the start of estrus synchronization, patches were scored using a 1 to 4 scale (1 = 0–25%; 2 = 25–50%; 3 = 50–75%; 4 = 75–100%) with scores of 3 or 4 considered activated. Blood samples were collected from each cow 10 days prior to, and at the start of the estrus synchronization. Serum progesterone concentrations were determined via radioimmunoassay; cows were considered estrous cycling if one or both samples exceeded a concentration of 0.5 ng/ml. Based on progesterone, 54.9% of cows were estrous cycling at the start of estrus synchronization. When missing patches were considered inconclusive results, use of patches to infer estrous cyclicity resulted in 85.0% sensitivity and 79.2% specificity with a positive predictive value of 87.2%. However, 75.1% of all cows presented with missing patches at the start of synchronization. If missing patches were considered activated, sensitivity was 95.7%, but specificity (16.4%) and PPV (58.2%) were poor, as 47.6% of cows presenting with missing patches were anestrous based on progesterone. Across all cows, pregnancy rate to AI was 58.0% (149/257). Cows with activated patches that were classified as false positives based on serum progesterone concentrations achieved a 71.4% (5/7) pregnancy rate to AI, raising questions as to whether sensitivity was underestimated due to inherent Type II errors in classification of cyclicity via progesterone. In summary, estrus detection aids are a sensitive tool to identify estrous cycling postpartum cows prior to the start of the breeding season; however, poor specificity and patch retention are limitations for this application.

Sex steroids and their relationship to binding proteins in the serum of the marmoset monkey (Callithrix jacchus)

1983 ◽  
Vol 96 (3) ◽  
pp. 443-450 ◽  
Author(s):  
J. K. Hodges ◽  
S. A. K. Eastman ◽  
N. Jenkins
Keyword(s):  
Sex Steroids ◽  
Luteal Phase ◽  
Inverse Relationship ◽  
Equilibrium Dialysis ◽  
Sex Hormone Binding Globulin ◽  
Binding Properties ◽  
Serum Progesterone ◽  
Pregnant Females ◽  
Marmoset Monkey ◽  
Steroid Binding

A sex hormone binding globulin (SHBG) similar to human SHBG was identified in marmoset serum based on its gel electrophoretic mobility, isoelectric point and steroid binding properties. Levels of serum SHBG were measured in immature and mature males, immature females and females during the luteal phase and pregnancy; serum progesterone, 5α-dihydrotestosterone (5α-DHT), testosterone, oestradiol-17β and oestrone were also measured. Mean (± s.e.m.) concentrations of SHBG in immature males (336 ±19 nmol/l) were higher (P <0·01) than those in mature males (251 ±13 nmol/l), whereas values in the groups of females were similar (359 ± 12, 395 ± 17, 397 ± 39 nmol/l in immature, non-pregnant and pregnant females respectively). There was an inverse relationship between SHBG and the levels of testosterone (r= −0·67) and 5α-DHT (r = −0·86) in males, but the correlation was significant (P <0·05) only for 5α-DHT. There was no correlation between levels of SHBG and oestrogens in males or between levels of SHBG and any of the steroids measured in females. Equilibrium dialysis was used to assess the percentage of steroid in serum in the unbound form. Mean percentage values for unbound testosterone and 5α-DHT were lower in immature males than in mature males (P <0·01) and negatively correlated with levels of SHBG (r = −0·78, testosterone; r = −0·56, 5α-DHT).

Seasonal and steroid-dependent effects on the modulation of LH secretion in the ewe by intracerebroventricularly administered β-endorphin or naloxone

1989 ◽  
Vol 122 (2) ◽  
pp. 509-517 ◽  
Author(s):  
R. J. E. Horton ◽  
H. Francis ◽  
I. J. Clarke
Keyword(s):  
Breeding Season ◽  
Luteal Phase ◽  
Pulse Frequency ◽  
Opioid Peptide ◽  
Follicular Phase ◽  
Oestrous Cycle ◽  
Opioid Antagonist ◽  
Endogenous Opioid ◽  
Endogenous Opioid Peptide ◽  
Lh Secretion

ABSTRACT The natural opioid ligand, β-endorphin, and the opioid antagonist, naloxone, were administered intracerebroventricularly (i.c.v.) to evaluate effects on LH secretion in ovariectomized ewes and in ovariectomized ewes treated with oestradiol-17β plus progesterone either during the breeding season or the anoestrous season. Ovary-intact ewes were also studied during the follicular phase of the oestrous cycle. Jugular blood samples were taken at 10-min intervals for 8 h and either saline (20–50 μl), 100 μg naloxone or 10 μg β-endorphin were injected i.c.v. after 4 h. In addition, luteal phase ewes were injected i.c.v. with 25 μg β-endorphin(1–27), a purported endogenous opioid antagonist. In ovariectomized ewes, irrespective of season, saline and naloxone did not affect LH secretion, but β-endorphin decreased the plasma LH concentrations, by reducing LH pulse frequency. The effect of β-endorphin was blocked by administering naloxone 30 min beforehand. Treating ovariectomized ewes with oestradiol-17β plus progesterone during the breeding season reduced plasma LH concentrations from 6–8 μg/l to less than 1 μg/l. In these ewes, saline did not alter LH secretion, but naloxone increased LH pulse frequency and the plasma concentrations of LH within 15–20 min. During anoestrus, the combination of oestradiol-17β plus progesterone to ovariectomized ewes reduced the plasma LH concentrations from 3–5 μg/l to undetectable levels, and neither saline nor naloxone affected LH secretion. During the follicular phase of the oestrous cycle, naloxone enhanced LH pulse frequency, which resulted in increased plasma LH concentrations; saline had no effect. In these sheep, β-endorphin decreased LH pulse frequency and the mean concentrations of LH, and this effect was prevented by the previous administration of naloxone. The i.c.v. administration of β-endorphin(1–27) to luteal phase ewes did not affect LH secretion. These data demonstrate the ability of a naturally occurring opioid peptide to inhibit LH secretion in ewes during the breeding and non-breeding seasons, irrespective of the gonadal steroid background. In contrast, whilst the gonadal steroids suppress LH secretion in ovariectomized ewes during both seasons, they only appear to activate endogenous opioid peptide (EOP)-mediated inhibition of LH secretion during the breeding season. Furthermore, these data support the notion that LH secretion in ovariectomized ewes is not normally under the control of EOP, so that naloxone has no effect. Journal of Endocrinology (1989) 122, 509–517

Passively immunizing ewes against inhibin during the luteal phase of the oestrous cycle raises the plasma concentration of FSH

1989 ◽  
Vol 123 (3) ◽  
pp. 383-391 ◽  
Author(s):  
G. E. Mann ◽  
B. K. Campbell ◽  
A. S. McNeilly ◽  
D. T. Baird
Keyword(s):  
Plasma Concentration ◽  
Luteal Phase ◽  
Passive Immunization ◽  
Oestrous Cycle ◽  
Ovulation Rate ◽  
Control Group ◽  
Pituitary Cells ◽  
Marked Rise ◽  
Peripheral Plasma

ABSTRACT Passive immunization was used to investigate the importance of inhibin in the negative feedback loop regulating the production of FSH in sheep. An antiserum raised to the 1–26 peptide fragment of the N-terminus of the α-chain of porcine inhibin was first shown to neutralize the suppressive effects of inhibin on the production of FSH by dispersed ovine pituitary cells in vitro. Groups of five mature Scottish Blackface ewes on day 8 of the luteal phase of the oestrous cycle were then injected with either 10 ml plasma from normal ewes (control) or 10 ml ovine inhibin antiserum. On day 10, luteal regression was induced by an i.m. injection of cloprostenol (100 μg), and ovulation rate determined 6 days later by laparoscopy. Peripheral plasma samples were collected throughout the experimental period. Following treatment, there was no change in the peripheral plasma concentration of LH in either group. Following injection of the inhibin antiserum, the concentration of FSH rose significantly (P<0·001) compared with the control group. The concentration of FSH rose from 1·42 ± 0·06 to a maximum of 2·58 ± 0·23 (s.e.m.) μg/l by 5·6 ±0·9 h, this maximum lasting 9·0±1·1 h. By 32·8 ±6·9 h, the concentration of FSH had returned to pretreatment levels, while the titre of free antibody in the plasma of treated ewes was still high. In the treated ewes, there were one single and four double ovulations compared with three single and two double ovulations in the control group, indicating that the inhibin immunization may have resulted in an increase in ovulation rate. We conclude that the marked rise in the plasma concentration of FSH following injection of inhibin antiserum provides strong evidence that inhibin is an important factor in the regulation of FSH production by the pituitary gland at this time. Journal of Endocrinology (1989) 123, 383–391

P–311 Association between serum sex hormones (progesterone and estradiol) and endometrial morphology during the mid-luteal phase

2021 ◽  
Vol 36 (Supplement_1) ◽  
Author(s):  
D Parvanov ◽  
R Ganeva ◽  
M Handzhiyska ◽  
N Vidolova ◽  
G Stamenov
Keyword(s):  
Scoring System ◽  
Luteal Phase ◽  
Morphological Characteristics ◽  
Serum Estradiol ◽  
Serum Progesterone ◽  
Glandular Cells ◽  
Mean Size ◽  
Stromal Edema ◽  
Estradiol Levels

Abstract Study question Is there a relationship between the serum progesterone and estradiol levels and certain morphological characteristics of human endometrium during the mid-luteal phase? Summary answer Serum progesterone is associated with the stromal edema and the abundance and size of basal vacuoles in the endometrium of women during the mid-luteal phase. What is known already Progesterone and estrogen are essential hormones that are necessary to prepare the endometrium for pregnancy. Their serum concentrations during the mid-luteal phase are important criteria for prediction of successful embryo implantation. In addition, a variety of endometrial morphological markers, such as the presence of pinopodes, subnuclear and supranuclear vacuoles, glandular secretion, and stromal edema have been applied for determination of the window of implantation and endometrial receptivity. However, the relationship between these endometrial morphological characteristics and serum levels of progesterone and estradiol is still scarcely studied. Study design, size, duration This is an observational study of 98 women, 25 to 46 years of age (mean 37 years), who had a blood sample and an endometrial biopsy during the mid-lutheal phase (LH + 7) in a natural cycle. The study was conducted between August 2020 and November 2020. Participants/materials, setting, methods Serum progesterone and estradiol were measured by electrochemiluminescence immunoassay (ECLIA) on the Cobas e411 analyser (Roche Diagnostics, Germany). The following endometrial morphological characteristics were assessed using light microscopy: (1) basal vacuoles (mean size and percentage of vacuolated glandular cells) (2) apical vacuoles (mean size and percentage of vacuolated glandular cells), (3) pinopodes (percentage of luminal epithelium covered in pinopodes), (4) glandular intraluminal secretion (6-level scoring system), (5) stromal edema (6-level scoring system). Main results and the role of chance The serum progesterone levels ranged between 0.39 and 145.3 ng/ml, with a median of 24.36 ng/ml. The serum estradiol levels varied between 26.91 and 842.89 pg/ml with a median of 124.75 pg/ml. The percentage of cells with basal vaculoles ranged from 0 to 90%, with a median of 38.57%, apical vacuoles (0–50%, 16.83%), pinopodes (0–80%, 23.87%), glandular intraluminal secretion (0–80%, 28.57%), and stromal edema (1–6, 1.42). To examine the association between the serum progesterone and estradiol and the studied endometrial morphological characteristics, the Spearman’s Rho Correlation coefficient for non-paramentric data was used. No correlation was found between serum estradiol levels and the studied morphological variables (p &gt; 0.05). In contrast, the serum progesterone concentration showed a significant negative correlation with the percentage of glandular epithelial cells with basal vacuoles (R= - 0.28; p = 0.03), the mean size of the basal vacuoles (R= - 0.24; p = 0.5) and a significant positive correlation with the stromal edema (R = 0.34; p &lt; 0.01). Limitations, reasons for caution The study was limited in sample size. Wider implications of the findings: The results of this study revealed that serum progesterone is more strongly associated with the occurrence of certain endometrial morphological characteristics during the mid-luteal phase than serum estradiol. These findings are valuable for development of new methods for accurate determination of the window of implantation. Trial registration number Not applicable

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