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This study examines whether exposure to ambient temperature in nineteenth-century urban space affected the ratio of boys to girls at birth. Furthermore, we investigate the details of temperature effects timing upon sex ratio at birth. The research included 66,009 individual births, aggregated in subsequent months of births for the years 1847-1900, i.e. 33,922 boys and 32,087 girls. The statistical modelling of the probability of a girl being born is based on logistic GAM with penalized splines and automatically selected complexity. Our research emphasizes the significant effect of temperature in the year of conception: the higher the temperature was, the smaller probability of a girl being born was observed. There were also several significant temperature lags before conception and during pregnancy. Our findings indicate that in the past, ambient temperature, similar to psychological stress, hunger, malnutrition, and social and economic factors, influenced the viability of a foetus. Research on the effects of climate on the sex ratio in historical populations may allow for a better understanding of the relationship between environmental factors and reproduction, especially concerning historical populations since due to some cultural limitations, they were more prone to stronger environmental stressors than currently.

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The secondary sex ratio (SSR), indicating the ratio of male to female live births, has garnered considerable attention within the realms of reproductive biology and public health. Numerous factors have been posited as potential trendsetters of the SSR. Given the extensive research on the impact of daily behaviors and habits on individuals' reproductive health, there is a plausible suggestion that lifestyle choices may also influence the SSR. By synthesizing the existing literature on the current research field, this comprehensive review indicates that an elevated SSR has been associated with an increased intake of fatty acids and monosaccharides, proper nutrition, higher educational levels, financial prosperity, and favorable housing conditions. On the other hand, a decreased SSR may be linked to undernutrition, socioeconomic disparities, and psychological distress, aligning with the Trivers-Willard hypothesis. Occupational factors, smoking habits, and cultural beliefs could also contribute to trends in the SSR. Our review underscores the significance of considering the aforementioned factors in studies examining the SSR and emphasizes the necessity for further research to unravel the mechanisms underpinning these connections. A more profound comprehension of SSR alterations due to lifestyle holds the potential to adequately develop public health interventions and healthcare strategies to enhance reproductive health and overall well-being.

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The secondary sex ratio (SSR), defined as the ratio of male to female offspring at birth, has garnered significant scientific interest due to its potential impact on population dynamics and evolution. In recent years, there has been a growing concern regarding the potential consequences of environmental chemicals on the SSR, given their widespread exposure and potential enduring ramifications on the reproductive system. While SSR serves as an indicator of health, ongoing research and scientific inquiry are being conducted to explore the potential relationship between chemicals and offspring ratio. Although some studies have suggested a possible correlation, others have yielded inconclusive results, indicating that the topic is intricate and still needs to be elucidated. The precise mechanism by which chemical agents exert their influence on the SSR remains ambiguous, with disruption of the endocrine system being a prominent justification. In light of the complex interplay between chemical exposure and SSR, the present review aims to comprehensively examine and synthesize existing scientific literature to gain a deeper understanding of how specific chemical exposures may impact SSR. Insights into chemical hazards that shift SSR patterns or trends could guide prevention strategies, including legislative bans of certain chemicals, to minimize environmental and public health risks.

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PURPOSE: The purpose of this study was to provide a detailed analysis of clinical and laboratory factors associated with skewed secondary sex ratio (SSR) after ART. METHOD: Retrospective cohort study of embryos resulting in live births, from frozen and fresh single blastocyst transfers. Embryos were cultured in either G-TL (n = 686) or Sage media (n = 685). Data was analyzed using a multivariate logistic regression model and a mixed model analysis. RESULTS: Significantly more male singletons were born after culture in Sage media compared to G-TL media (odds ratio (OR) 1.34, 95% CI (1.05, 1.70), P = 0.02). Inner cell mass grade B vs A (OR 1.36 95% CI (1.05, 1.76), P = 0.02) and one previous embryo transfer (OR 1.49, 95% CI (1.03, 2.16), P = 0.03) were associated with a significantly higher probability of male child at birth. Factors associated with a reduced probability of male child were expansion grade 3 vs 5 (OR 0.66, 95% CI (10.45, 0.96), P = 0.03) and trophectoderm grade B vs A (OR 0.57, 95% CI (0.44, 0.74), P = 0.00). Male embryos developed significantly faster in Sage media compared to G-TL media for the stages of blastocyst (- 1.12 h, 95% CI (- 2.12, - 0.12)), expanded blastocyst (- 1.35 h, 95% CI (- 2.34, - 0.35)), and hatched blastocyst (- 1.75 h, 95% CI (- 2.99, - 0.52)). CONCLUSION: More male children were born after culture in Sage media compared to G-TL media. Male embryo development was affected by culture media. Our observations suggest that culture media impact male embryo quality selectively, thus potentially favoring the selection of male embryos.

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BACKGROUND: Evidence for the association between earthquakes and adverse perinatal outcomes is limited. OBJECTIVES: To evaluate the association between earthquakes and perinatal outcomes including preterm birth and low birth weight. SEARCH STRATEGY: We searched studies using MEDLINE, Cochrane Central Register of Controlled Trials, EMBASE, World Health Organization International Clinical Trials Platform Search Portal, and ClinicalTrials.gov on February 9, 2023. SELECTION CRITERIA: We included before-and-after studies that evaluated the associations between earthquakes and perinatal outcomes in women living in affected areas. DATA COLLECTION AND ANALYSIS: Two independent reviewers extracted data. We calculated the pooled odds ratio (OR) with the random-effects model. We analyzed outcomes in subgroups of Asians and others. We evaluated the certainty of evidence with the Grading of Recommendations Assessment, Development and Evaluation system. MAIN RESULTS: We included 2 607 405 women in 13 studies. Earthquakes may not increase preterm birth (nine studies, 1 761 760 participants: OR 1.10, 95% confidence interval [CI] 0.98-1.24, low certainty of evidence) or low birth weight (seven studies, 1 753 891 participants: OR 1.10, 95% CI 0.94-1.28, low certainty of evidence). Subgroup analyses showed that earthquakes may be associated with an increase of preterm birth among populations in Asia (OR 1.44, 95% CI 1.07-1.95), but this was not evident in others (OR 0.93, 95% CI 0.83-1.05). CONCLUSIONS: Perinatal outcomes might not change after earthquakes. Further research on the association between earthquakes and perinatal outcomes, combined with an assessment of the characteristics of the region, is needed.

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BACKGROUND: Assisted reproduction technology (ART) has advanced significantly, raising concerns regarding its impact on the secondary sex ratio (SSR), which is the sex ratio at birth in offspring. This study aimed to explore factors affecting SSR in singletons, singletons from twin gestation, and twins from twin gestation within the context of ART. METHODS: A retrospective analysis was conducted on data from 8335 births involving 6,223 couples undergoing ART. Binary logistic regression assessed relationships between parental and embryonic factors and SSR in singletons and singletons from twin gestation. Multinomial logistic regression models were utilized to identify factors influencing SSR in twins from twin gestation. RESULTS: Secondary infertility (OR = 1.164, 95% CI: 1.009-1.342), advanced paternal age (OR = 1.261, 95% CI: 1.038-1.534), and blastocyst embryo transfer (OR = 1.339, 95% CI: 1.030-1.742) were associated with an increased SSR, while frozen embryo transfer (FET) showed a negative association with SSR (OR = 0.738, 95% CI: 0.597-0.912) in singletons. A longer duration of gonadotropin (Gn) usage reduced SSR in singletons (OR = 0.961, 95% CI: 0.932-0.990) and singletons from twin gestation (OR = 0.906, 95% CI: 0.838-0.980). In singletons from twin gestation, male-induced infertility (OR = 2.208, 95% CI: 1.120-4.348) and higher Gn dosage (OR = 1.250, 95% CI: 1.010-1.548) were significantly associated with an increased SSR. Women aged > 35 years and intracytoplasmic sperm injection (ICSI) were associated with lower SSR (OR = 0.539, 95% CI: 0.293-0.990 and OR = 0.331, 95% CI: 0.158-0.690, respectively). In twins from twin gestation, paternal age exceeded maternal age (OR = 0.682, 95% CI: 0.492-0.945) and higher Gn dosage (OR = 0.837, 95% CI: 0.715-0.980) were associated with a higher proportion of male twins. Cleavage stage transfer (OR = 1.754, 95% CI: 1.133-2.716) resulted in a higher percentage of boy-girl twins compared to blastocyst transfer. CONCLUSION: This study demonstrates the complex interplay of various factors in determining the SSR in ART, highlighting the importance of considering infertility type, paternal age, fertilization method, embryo transfer stage, and Gn use duration when assessing SSR. Nevertheless, further research with a large sample size is necessary to confirm and expand upon the findings of this study.

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Studying the nesting biology of wasp and bee species provides valuable insights into the ecology and evolution of these insects, shedding light on their ecological significance and aiding in their conservation efforts. Trypoxylon Latreille, 1796 is a genus of spider-hunting wasps that provisions their brood with paralyzed preys. This study focuses on aspects of nesting biology of Trypoxylon (Trypargilum) species such as sex ratio, sexual dimorphism, and morphometric variation at both inter- and intraspecific levels. The secondary sex ratio (SR) exhibited variation among species and populations. Males predominantly emerged from the first brood cells and from trap nests with smaller diameters. In comparison, females showed significantly larger body mass and linear wing measurements than males. Procrustes ANOVA values for centroid size (CS) and wing shape (SH) indicated significant differences in both wing size and shape among the five analyzed Trypoxylon species. Sexual dimorphism indices (SDI) derived from centroid size were found to be similar to those obtained from linear measurements, while SDI values based on body mass were significantly higher. Nests containing a greater number of cells tended to produce a larger number of higher-quality males and females. This observation, along with the lower coefficient of variation for female body size and high heritability, suggests that this trait may be subject to natural selection. Further studies that estimate the size of parents and their respective offspring are necessary to confirm the fitness advantage associated with larger female sizes in Trypoxylon species.

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RESEARCH QUESTION: To determine whether blastocyst quality affects the sex ratio at birth through a single blastocyst frozen - thawed embryo transfer (SBFET) cycle. DESIGN: In this retrospective analysis, we examined 3,041 singleton infants born following SBFET between 2017 and 2020 at a single institution. We compared the sex ratios of these infants with respect to the blastocyst quality, embryo growth rate, and morphology. RESULTS: The main outcomes of this study were that the sex ratio (M/F) at birth of SBFET was 1.24. Mothers >40 years old had a considerably lower sex ratio than mothers <40 years old (0.39 vs. 1.23-1.28, p < .05). Transplanting high-quality blastocysts significantly increased the proportion of boys born (1.29 vs. 0.88, p < .05). There were no significant differences in the sex ratio with respect to the inner cell mass (ICM) score and expansion degree. Additionally, a high trophoblastic cell (TE) score resulted in a significantly higher sex ratio than the TE score with C (1.62 vs. 1.15 vs. 0.85, p < .001). Multivariable logistic regression analysis was performed to determine which variables were significant factors affecting sex ratio, and the outcomes were consistent with previous findings. CONCLUSIONS: Our study indicated that high-quality, especially good TE score, had a higher chance of resulting in a male infant than a female infant.

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Commercial dairy producers may get frustrated by the lower ratio of female to male calves born because female calves are more valuable than bull calves. Our objective was to determine if parity or stage of lactation at the time of breeding, using conventional semen, influenced the sex of the calf. Data from the University of Illinois and the University of New Hampshire dairy herds were collected and summarized for calf sex, the number of services to achieve a calf and the lactation number when conception of that calf occurred. Logistical regression procedures were used to analyze the dataset via version 9.4 of SAS. The final dataset contained 2,987 calvings, which consisted of 1,406 females and 1,581 males (47.1% and 52.9% for females and males, respectively). The frequency distribution of the number of services to achieve a calf was highest for the first service and progressively declined with increasing services (52.06%, 21.66%, 10.75%, 6.66%, 4.22%, and 4.65% for 1 to 6 services, respectively). The frequency distribution of calvings by lactation number was greatest for first lactation cows becoming pregnant with their second calf and declined with increasing parity (35.49%, 28.22%, 17.01%, 9.61%, 5.02%, 2.51%, 1.14%, 0.70%, and 0.30% for lactation numbers 1 to 9, respectively). Logistic stepwise regression indicated that the number of services to achieve a calf was significant in predicting the ratio of female to male calves. Calculation of odds ratios indicated that as the lactation number increased the likelihood of getting a bull calf decreased. Parity, services, and parity by services interaction were significant for cows having a greater number of parities and cows with a greater number of services yielding more heifer calves. However, an interaction occurred where cows with greater number of services along with greater parities more likely to have a bull calf. These data provide evidence that increasing the number of services to achieve a calf and increasing age of the cow increased the probability of a heifer calf being born. These data indicate that cows with greater parties (lesser cull rate) are more likely to produce heifer calves.

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Selection of best blastocyst is crucial in single blastocyst transfer cycles, which is based on blastocyst morphological parameters such as inner cell mass (ICM), trophectoderm (TE) and its inner diameter. We aimed to study relation between morphological parameter and sex ratio after single vitrified-warmed blastocyst transfer (SVBT). Current study based on data of single-center and performed by retrospective analysis of 1563 SVBT (911 patients) with minimal stimulation on 5th and 6th days. TE morphology, female age and blastocyst day are highly correlated with clinical pregnancy rate (CPR) and live birth rate (LBR). Also, A grade ICM significantly correlated with CPR than C grade. Additionally, probability of being male gender is 2.8 times higher in singleton live birth with A grade trophectoderm than C grade. Neither ICM morphology, LBR nor sex ratio were not related to trophoectoderm grade. Higher grade TE, younger the age of patient and selection of the day 5 blastocyst showed higher frequency of CPR and LBR. Therefore, consideration of these parameters is a better method to select the best embryo. On the other hand, the selection for transfer blastocyst based on quality and morphological parameters may inadvertently push the secondary sex ratio (SSR) in favor of female births.

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PURPOSE: Assisted reproductive technology (ART) has an impact on secondary sex ratio (SSR), which is seemed to be elevated after blastocyst transfer (BT) but decreased following ICSI procedure. We aim to assess whether the higher SSR associated with BT could be influenced by fertilization method used. METHODS: All consecutive IVF/ICSI cycles (fresh and frozen) involving single embryo transfer (SET) resulting in a live birth between 2015 and 2019 were retrospective analyzed. Logistic regression was used to model the effect on the SSR of maternal and specific ART characteristics. RESULTS: Six thousand nine hundred twenty-two women were included with the crude SSR of 54.8%. The impact of BT on SSR is influenced by the fertilization method used. After adjustment for potential confounders, the SSR in the ICSI BT group was significantly higher when compared to ICSI cleavage-stage embryo SET (aOR 1.24; 95% CI 1.10-1.40, P < 0.001). However, this effect was not detected among SBT with IVF treatment (aOR 1.04; 95% CI 0.97-1.12, P = 0.260). Assessing blastocyst morphological parameters, high trophectoderm quality was significantly associated with elevated SSR (aOR 1.76, 95% CI 1.34-2.31 [A vs. C], and aOR 1.28, 95% CI 1.14-1.44 [B vs. C]). No significant difference was shown in expansion, inner cell mass, or days of blastocyst formation between male and female blastocysts. CONCLUSIONS: The impact of BT on SSR could be influenced by the fertilization method used. The higher SSR was observed after BT with ICSI procedures but not with IVF. Interpretation of the findings is limited by the potential for selection and confounding bias.

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A decline in the proportion of male births (secondary sex ratio, SSR) has been seen in several countries including Japan in recent years. Although previous studies have reported that the SSR is affected by exposure to chemical substances such as dioxins and polychlorinated biphenyls, as well as heavy metals such as methylmercury, the effects of lead exposure on the SSR have been little studied. The aim of this study was to determine the association between maternal lead exposure and SSR. In a large-scale nationwide birth cohort study, maternal blood lead level (BLL) was determined using whole blood from the second or third trimester of pregnancy. The association between SSR and maternal BLL was estimated using multivariable logistic models. Binomial distribution was applied to examine the differences in SSR by dividing the participants into five groups based on BLL. The primary outcome was SSR, and the child sex was obtained from the medical record transcripts. Of 104,062 fetal records, 85,171 were examined for analysis. The median maternal BLL was 5.85 ng/g (5th-95th percentile 3.45-10.6 ng/g). The overall proportion of males among participating infants was 0.512. In logistic regression models adjusted for covariates, the analysis revealed an increased odds ratio for SSR with higher blood lead concentrations [Group 2: adjusted OR 1.082, 95% confidence interval 1.037 to 1.129, Group 3: 1.122, 1.074 to 1.171, Group 4: 1.214, 1.163 to 1.268, Group 5: 1.279, 1.224 to 1.336]. Compared to the general birth probability in Japan, the group with low BLL had a lower SSR and the group with high BLL had a higher SSR. Higher maternal lead exposures during pregnancy were associated with increased SSR. Further investigations including assessment of paternal lead exposure are necessary to understand the association between lead exposure and SSR.

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BACKGROUND AND OBJECTIVES: The sex ratio of human birth cohorts predicts the health and longevity of their members. Most literature invokes natural selection in support of the argument that heritable tendencies to produce male or female offspring induce oscillation in the sex ratio and its sequelae. Tests of the argument remain exceedingly rare because they require vital statistics describing many generations of a population both unaffected by migration and exposed to an exogenous stressor virulent enough to change the sex ratio at birth. We contribute to the literature by using time-series modeling to detect oscillation in the best data currently available for such a test. METHODOLOGY: We apply rigorous time-series methods to data describing Sweden from 1751 through 1830, a period when the population not only aged in place without migration, but also exhibited the effects of an Icelandic volcanic eruption including a historically low secondary sex ratio. That very low sex ratio should have induced oscillation if heritable mechanisms appear in humans. RESULTS: We detected oscillation in the ratio but not that predicted by heritable tendencies to produce males or females. We found peak-to-trough oscillation at 14 rather than the approximately 32 years expected from the heritable tendencies argument. CONCLUSIONS AND IMPLICATIONS: Our findings suggest that mechanisms other than perturbation of heritable tendencies to produce males or females induce oscillation in the human secondary sex ratio. These other mechanisms may include reproductive suppression and selection in utero. LAY SUMMARY: The male to female ratio in human birth cohorts predicts longevity but its variation over time remains unexplained. We test the long-held theory that the ratio oscillates due to heritable tendencies to produce males or females. We find oscillation, but it appears due to social processes rather than heritable mechanisms.

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BACKGROUND: The aim of this study was to determine the secondary sex ratio (SSR) of offspring in assisted reproduction technology (ART) in Jilin Province, China, and to analyse the influencing factors associated with SSR. METHODS: A cross-sectional study of 3833 babies including singletons and twins born to 2990 couples treated by ART between May 2011 and December 2018 was performed. RESULTS: The main outcomes of this study were that the SSR of ART babies in Jilin Province was 50.64% and the SSR was associated with fertilization methods (p < 0.05). Comparing to in vitro fertilization (IVF), intracytoplasmic sperm injection (ICSI) (OR = 0.808, 95%CI: 0.681-0.958) decreased the percentage of male babies. CONCLUSIONS: This study suggests that the SSR of ART births in Jilin Province was lower than the normal level and ICSI had a significant effect on SSR. Though we need more samples to study in the future, we still need to think about the impact of ICSI on SSR in ART.

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Maternal prenatal stress influences offspring neurodevelopment and birth outcomes including the ratio of males to females born; however, there is limited understanding of what types of stress matter, and for whom. Using a data-driven approach with 27 variables from questionnaires, ambulatory diaries, and physical assessments collected early in the singleton pregnancies of 187 women, 3 latent profiles of maternal prenatal stress emerged that were differentially associated with sex at birth, birth outcomes, and fetal neurodevelopment. Most women (66.8%) were in the healthy group (HG); 17.1% were in the psychologically stressed group (PSYG), evidencing clinically meaningful elevations in perceived stress, depression, and anxiety; and 16% were in the physically stressed group (PHSG) with relatively higher ambulatory blood pressure and increased caloric intake. The population normative male:female secondary sex ratio (105:100) was lower in the PSYG (2:3) and PHSG (4:9), and higher in the HG (23:18), consistent with research showing diminished male births in maternal stress contexts. PHSG versus HG infants were born 1.5 wk earlier (P < 0.05) with 22% compared to 5% born preterm. PHSG versus HG fetuses had decreased fetal heart rate-movement coupling (P < 0.05), which may indicate slower central nervous system development, and PSYG versus PHSG fetuses had more birth complications, consistent with previous findings among offspring of women with psychiatric illness. Social support most strongly differentiated the HG, PSYG, and PHSG groups, and higher social support was associated with increased odds of male versus female births. Stress phenotypes in pregnant women are associated with male vulnerability and poor fetal outcomes.

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STUDY QUESTION: Does ART impact the secondary sex ratio (SSR) when compared to natural conception? SUMMARY ANSWER: IVF and ICSI as well as the stage of embryo transfer does impact the overall SSR. WHAT IS KNOWN ALREADY: The World Health Organization quotes SSR for natural conception to range between 103 and 110 males per 100 female births. STUDY DESIGN SIZE DURATION: A total of 1 376 454 ART cycles were identified, of which 1 002 698 (72.8%) cycles involved IVF or ICSI. Of these, 863 859 (85.2%) were fresh cycles and 124 654 (12.4%) were frozen cycles. Missing data were identified in 14 185 (1.4%) cycles. PARTICIPANTS/MATERIALS SETTING METHODS: All cycles recorded in the anonymized UK Human Fertilisation and Embryology Authority (HFEA) registry database between 1991 and 2016 were analysed. All singleton live births were included, and multiple births were excluded to avoid duplication. MAIN RESULTS AND THE ROLE OF CHANCE: The overall live birth rate per cycle for all IVF and ICSI treatments was 26.2% (n = 262 961), and the singleton live birth rate per cycle was 17.1% (n = 171 399). The overall SSR for this study was 104.0 males per 100 female births (binomial exact 95% CI: 103.1-105.0) for all IVF and ICSI cycles performed in the UK recorded through the HFEA. This was comparable to the overall SSR for England and Wales at 105.3 males per 100 female births (95% CI: 105.2-105.4) from 1991 to 2016 obtained from the Office of National Statistics database. Male predominance was seen with conventional insemination in fresh IVF treatment cycles (SSR 110.0 males per 100 female births; 95% CI: 108.6-111.5) when compared to micro-injection in fresh ICSI treatment cycles (SSR 97.8 males per 100 female births; 95% CI: 96.5-99.2; odds ratio (OR) 1.16, 95% CI 1.12-1.19, P < 0.0001), as well as with blastocyst stage embryo transfers (SSR 104.8 males per 100 female births; 95% CI: 103.5-106.2) when compared to a cleavage stage embryo transfer (SSR 101.2 males per 100 female births; 95% CI: 99.3-103.1; OR 1.03, 95% CI 1.01-1.06, P = 0.011) for all fertilization methods. LIMITATIONS REASONS FOR CAUTION: The quality of the data relies on the reporting system. Furthermore, success rates through ART have improved since 1991, with an increased number of blastocyst stage embryo transfers. WIDER IMPLICATIONS OF THE FINDINGS: This is the largest study to date evaluating the impact of ART on SSR. The results demonstrate that, overall, ART does have an impact on the SSR when assessed according to the method of fertilization (ICSI increased female births while IVF increased males). However, given the ratio of IVF to ICSI cycles at present with 60% of cycles from IVF and 40% from ICSI, the overall SSR for ART closely reflects the population SSR for, largely, natural conceptions in England and Wales. STUDY FUNDING/COMPETING INTERESTS: The study received no funding. C.M.B. is a member of the independent data monitoring group for a clinical endometriosis trial by ObsEva. He is on the scientific advisory board for Myovant and medical advisory board for Flo Health. He has received research grants from Bayer AG, MDNA Life Sciences, Volition Rx and Roche Diagnostics as well as from Wellbeing of Women, Medical Research Council UK, the NIH, the UK National Institute for Health Research and the European Union. He is the current Chair of the Endometriosis Guideline Development Group for ESHRE and was a co-opted member of the Endometriosis Guideline Group by the UK National Institute for Health and Care Excellence (NICE). I.G. has received research grants from Wellbeing of Women, the European Union and Finox. TRIAL REGISTRATION NUMBER: Not applicable.

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BACKGROUND: Some studies have suggested that blastocyst transfer is associated with i) imbalance in the secondary sex ratio (SSR) (which favors male offspring), ii) increased incidence of monozygotic twins (MZT). In contrast, others have not found these changes. In this study, we evaluated the association between blastocyst transfer and SSR and MZT, considering potential parental confounders. METHODS: The Japan Environment and Children's Study is a large, nationwide longitudinal birth cohort study funded by the Ministry of the Environment of Japan. We used this large dataset, including 103,099 pregnancies, to further investigate the association between blastocyst transfer, SSR and MZT, using spontaneously conceived pregnancies, non-assisted reproductive technology (non-ART) treatment (intrauterine insemination and ovulation induction with timed intercourse) and cleavage stage embryo transfer for comparison. We evaluated the association with each group, the SSR, and the frequency of MZT, calculating the adjusted odds ratio (AOR) using multivariable logistic regression analyses, adjusting for potential parental confounders such as basic health and socioeconomic status. RESULTS: For each group (spontaneous conception vs. non-ART treatment vs. cleavage stage embryo transfer vs. blastocyst transfer), the percentages of males were 51.3% vs 50.7% vs 48.9% vs 53.4% and the monozygotic twinning rates per pregnancy were 0.27% vs 0.11% vs 0.27% vs 0.99% respectively. Multivariate logistic regression analyses indicated that blastocyst transfer was significantly associated with a higher SSR and higher incidence of MZT than the other three groups (SSR: AOR 1.095, 95% CI1.001-1.198; MZT: AOR 4.229, 95% CI 2.614-6.684). CONCLUSIONS: There are significant relationships between blastocyst transfer and SSR imbalance and a higher occurrence of MZT.

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RESEARCH QUESTION: What is the association between assisted reproductive technologies and human sex ratio as a proportion of male offspring at birth. DESIGN: A total of 59,628 singleton deliveries resulting from IVF, intracytoplasmic sperm injection (ICSI) and intrauterine insemination (IUI) or ovulation induction from 101 IVF clinics in Germany, that had been documented in a national German IVF registry, were analysed. Sex ratio after assisted reproductive technology was also compared with the sex ratio reported in the birth records of the German Federal Statistical Office. RESULTS: The sex ratio was 50.0% (95% CI 49.5% to 50.5%) for ICSI, 52.2% (95% CI 51.5% to 52.9%) for IVF, 52.2% (95% CI 50.9% to 53.5%) for IUI or ovulation induction and 51.3% in the national birth records, respectively. Significant differences existed across the three treatment groups (P = 6.86 × 10-7) as well as in pairwise comparisons between ICSI versus IVF (P = 6.88 × 10-7) and ICSI versus IUI or ovulation induction (P = 0.003). No difference existed between the groups IUI or ovulation induction versus IVF. Same results were also present after stratification by maternal age: IVF versus ICSI (P = 6.433 × 10-7), ICSI versus IUI or ovulation induction (P = 0.003), and IVF versus IUI or ovulation induction (non-significant). Compared with the national birth records, ICSI is associated with a lower sex ratio compared with the reference group (P < 0.001), whereas IVF is associated with a higher sex ratio (P = 0.015). CONCLUSIONS: The use of ICSI is associated with an equal proportion of sexes at birth, which is not the case for IVF, IUI or ovulation induction, or natural conception. This phenomenon is not influenced by maternal age.

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BACKGROUND: Toxoplasma gondii is a protozoan parasite with worldwide distribution, infecting a broad-range of humans and warm-blooded animals. In the current study, role of this parasite on secondary sex ratio and risk of miscarriage was investigated. METHODS: In this cross-sectional study, 850 cord blood samples were collected in Tehran, Iran, 2014-2015. Enzyme-linked immunosorbent assay (ELISA) was used to assess anti-Toxoplasma IgG in samples. Information such as sex of the neonates and age, number of previous pregnancies and history of miscarriage of the mothers were recorded in questionnaires. Logistic regression analysis was used to assess the possible relationship between the latent toxoplasmosis and the highlighted parameters. RESULTS: Logistic regression analysis showed that the odds of having a male neonate in seropositive women is nearly 64% higher than that in seronegative women (OR = 1.64, CI95 = 1.16-2.33, P = 0.005). The odds ratio of having male neonate increased to 2.10 (CI95 = 1.24-3.57, P = 0.006) in high-titer seropositive women, compared to that in seronegative control group. The odds of having a miscarriage history was approximately two and a half times greater in seropositive women than in seronegative ones (OR = 2.45, CI95 = 1.56-3.87, P < 0.001). The odds ratio of having miscarriage increased to 2.76 (CI95 = 1.61-4.73, P < < .001) in low-titer seropositive women, compared to that in seronegative control group. CONCLUSION: Results of the current study have shown that T. gondii infection affects secondary sex ratio in human offspring and can be addressed as one of the major miscarriage causes in women.

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Sex allocation theory predicts that parents bias the offspring sex ratio strategically. In avian species, the offspring sex ratio can be biased at multiple growth stages, although the mechanisms are not well known. It is crucial to reveal a cause and timing of biased offspring sex ratio. We investigated (i) offspring sex ratio at multiple growth stages, from laying to fledging; and (ii) the stage at which offspring sex ratio became biased; and (iii) the cause of biased offspring sex ratio in Eurasian tree sparrows Passer montanus. Sex determination of 218 offspring, including hatchlings and unhatched eggs from 41 clutches, suggested that the offspring sex ratio was not biased at the egg-laying stage but was significantly female-biased after the laying stage due to higher mortality of male embryos. Half of the unhatched eggs showed no sign of embryo development (37/74, 50.00%), and most undeveloped eggs were male (36/37, 97.30%). Additional experiments using an incubator suggested that the cause of embryo developmental failure was a lack of developmental ability within the egg, rather than a failure of incubation. This study highlights the importance of clarifying offspring sex ratio at multiple stages and suggests that offspring sex ratio is adjusted after fertilization.