RESUMEN
Background/Objectives: Semen cryopreservation is routinely performed in fertility clinics for a variety of reasons, including fertility preservation and storage of donor sperm, yet the freeze-thaw process leads to cellular damage via ice crystal formation, osmotic shock, and supraphysiological levels of oxidative stress. Sperm resistance to damage during the freeze-thaw process varies widely, yet the intrinsic factors associated with sperm cryotolerance are largely unknown. The study aimed to investigate whether poor chromatin condensation renders sperm vulnerable to DNA fragmentation and cell death induced by the freeze-thaw process. Methods: Participants (n = 51) from the general community who met the inclusion criteria collected a semen sample after 3-8 days of abstinence. Neat semen samples underwent traditional semen analysis, aniline blue (AB)-eosin staining for chromatin condensation, the terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL) assay for DNA fragmentation, and the Annexin V assay for apoptosis/necrosis, prior to being cryopreserved using the liquid nitrogen vapour method and stored at -196 °C. Stored samples were later thawed at room temperature and processed using density gradient centrifugation. Motile sperm concentration, DNA fragmentation and apoptosis/necrosis were analysed in post-thaw samples. Results: As indicated by a significant interaction effect in linear mixed models, an increased proportion of AB-positive sperm in the pre-freeze sample exacerbated the adverse effect of freezing on sperm DNA fragmentation (p = 0.004), late apoptosis (p = 0.007), and necrosis (p = 0.007). AB-staining was positively correlated with all three parameters in the post-thaw sample (all rs ≥ 0.424, all p < 0.01) and remained significant after adjusting for neat sperm concentration (all partial rs ≥ 0.493, all p < 0.01). Similarly, AB-staining was significantly correlated with the percentage point change in sperm DNA fragmentation (rs = 0.366, p = 0.014) and necrosis (rs = 0.403, p = 0.009), both of which remained significant after adjusting for neat sperm concentration (both partial rs ≥ 0.404, both p < 0.01), and borderline significantly correlated with percentage point change in late apoptosis (rs = 0.307, p = 0.051). Conclusions: Sperm with poorly condensed chromatin may be more susceptible to cellular damage during the freeze-thaw process, independent of pre-freeze sperm concentration. These findings may help to explain the intrinsic variation in sperm resistance to cryodamage within and between individuals that is poorly understood.
RESUMEN
PURPOSE: To identify and characterise appropriate comparison groups for population studies of health outcomes in ART-conceived births: ovulation induction (OI), subfertile untreated and fertile natural conceptions. Our secondary objective was to examine whether known risks of pregnancy complications and adverse birth outcomes in ART births are elevated in comparison with subfertile (untreated and OI) conception groups. METHODS: We linked State and Commonwealth datasets to identify all live and stillbirths (≥ 20 weeks) in Western Australia from 2003 to 2014 by method of conception. Demographic characteristics, maternal pre-existing conditions, adverse obstetric history and pregnancy complications were compared across conception groups. Generalised estimating equations were used to estimate adjusted risk ratios (aRRs) and 95% confidence intervals (CI) for pregnancy complications and birth outcomes in singletons. RESULTS: We identified 9456 ART, 3870 OI, 11,484 subfertile untreated and 303,921 fertile naturally conceived deliveries. OI and subfertile untreated groups more closely resembled the ART group than the fertile group; however, some differences remained across parity, maternal age, pre-existing conditions and obstetric history. In multivariate analyses, ART singletons had greater risks of placental problems (e.g. placenta praevia aRR 2.42 (95% CI 1.82-3.20)) and adverse birth outcomes (e.g. preterm birth aRR 1.38 (95% CI 1.25-1.52)) than the subfertile untreated group, while OI singletons were more similar to the subfertile group with higher risk of preeclampsia and gestational diabetes. CONCLUSION: OI and subfertile untreated conception groups offer improved options for interpreting health outcomes in ART births. Pregnancy complications (particularly placental disorders) and adverse outcomes at delivery are more common following ART.
