LAY SUMMARY When embryos are frozen and thawed for fertility treatment, they sometimes collapse, but does this mean they are no longer viable? This study followed 438 frozen embryo transfer cycles to understand whether collapsed embryos can recover, and whether giving them more time in the incubator before transfer makes a difference. The key finding is that what matters most is how an embryo looks at the time of transfer, not immediately after thawing. Embryos that re-expanded before being transferred had similar success rates to those that never collapsed. Only embryos that remained collapsed at transfer had significantly poorer outcomes. Importantly, for every additional hour spent in the incubator, a collapsed embryo's odds of recovering improved substantially. This means that rather than discarding a collapsed embryo, clinicians may simply need to wait, giving it time to recover could meaningfully improve the chances of a successful pregnancy. Collapsed embryos that are given longer to recover in the incubator before transfer may have the same chance of achieving a pregnancy as embryos that never collapsed.
LAY SUMMARY In pigs, not all piglets grow the same before birth, even when they develop in the same pregnancy. However, these differences are often overlooked. This review describes some of the reasons why piglets within a litter can grow differently. As litter size increases, piglets must share limited space and nutrients in the uterus, creating competition during development. Differences can begin very early in pregnancy and may depend on where each fetus is located in the uterus. The sex of the fetus and neighboring fetuses may also influence growth and development. Together, these factors mean that each fetus develops under different conditions, which can affect birth weight, survival, and later performance. Understanding why these differences occur may help identify ways to produce more uniform litters and improve piglet survival and productivity.
AbstractWhile biological and lifestyle determinants of reproductive health are well documented globally, comprehensive data integrating socio-demographic, lifestyle, and health correlates within a contemporary Polish context remain limited. This study aimed to estimate the prevalence and identify correlates of self-reported fertility problems among adults completing a 2024 online survey in Poland (the National Fertility Test). Of the 8,000 respondents surveyed, the analytical sample comprised 5,532 (3,316 women and 2,216 men) who had attempted to conceive. Sex-specific, age-adjusted, Holm–Bonferroni-corrected logistic regression assessed associations between socio-demographic, lifestyle, and health variables and fertility problems. Within the analytical sample, 28.9% of respondents reported fertility problems (36.6% of women and 17.4% of men). In women, the strongest associations were observed for fallopian tube obstruction (OR = 23.0), polycystic ovary syndrome (OR = 5.35), and endometriosis (OR = 2.82), whereas a history of prior pregnancy (OR = 0.26) and better self-rated mental health (OR = 0.76) were associated with lower odds. In men, associations were limited to the use of reproductive supplements (OR = 4.06), varicocele or epididymal cysts (OR = 3.08), and a history of sexually transmitted infection (OR = 4.60). In both sexes, associations with behaviours such as supplement use and specific conception strategies likely reflect reverse causation, marking active help-seeking rather than causal risk factors. Given the self-selected sampling method, these findings should not be interpreted as population-level prevalence estimates for Poland, but confirm established clinical correlates alongside distinct socio-demographic and lifestyle patterns, underscoring the need for targeted reproductive health education. Lay summaryThis study examined the frequency of fertility struggles among 8,000 Polish adults through the 2024 National Fertility Test, a nationwide online survey. Of the 5,532 participants who had attempted to conceive, 28.9% reported such difficulties.Factors linked to these struggles differed by sex.For women, conditions such as fallopian tube obstruction, polycystic ovary syndrome (PCOS), thyroid disease, or endometriosis were among the strongest factors; a history of prior pregnancy and better self-reported mental health were both linked to lower odds of reporting current problems.For men, varicocele or epididymal cysts and a history of sexually transmitted infection were the clearest factors identified.Due to the self-selected online nature of this cohort, results likely reflect participation bias from people currently attempting to conceive. Overall, the study underscores significant reproductive challenges in Poland, highlighting a strong, critical need for better health education and support tailored specifically to the Polish public.
