Men born small for gestational age or with low birth weight do not improve their rate of reproduction over time: a Swedish population-based study.

OBJECTIVE: To investigate whether the reduced reproductive rate among men born small for gestational age (SGA) or with low birth weight (LBW) is present after up to 44 years of follow-up. DESIGN: Population-based register study. SETTING: National registers in Sweden. PATIENT(S): All men born in Sweden between 1973 and 1993 (n = 1,045,167) followed up to 2018. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): Registered fatherhood, infertility diagnoses, and fertility treatments obtained from registers up to 2018 RESULT(S): Men born SGA or with LBW have a lower chance of becoming fathers than men born with normal birth characteristics: hazard ratio (95% confidence interval) 0.91 (0.90-0.92) and 0.88 (0.86-0.90), respectively. The reduction in reproductive rate is more evident after a longer follow-up time. Men born SGA were more likely to receive a diagnosis of infertility. Sperm donation and intracytoplasmic sperm injection were more often used in men born SGA, further strengthening the hypothesis of an association between birth characteristics and male infertility. CONCLUSION(S): Men born SGA or with LBW have a lower chance of becoming fathers, but the reduction in fertility is smaller for the younger cohort. Further studies are needed to determine if this difference is maintained.

Men becoming fathers by intracytoplasmic sperm injection were more often born small for gestational age.

Being born with nonoptimal birth characteristics decreases the chance of becoming a father. Urogenital malformations as well as metabolic syndrome are more common in men born small for gestational age (SGA) and could be contributing factors to the reduced fertility rate seen in these men. It could imply that men becoming fathers by assisted reproductive technology (ART) more often are born with low birth weight (LBW), preterm, and/or SGA than men conceiving without treatment and also that men where intracytoplasmic sperm injection (ICSI) had to be performed more often are born with nonoptimal birth characteristics than men where conventional in vitro fertilization (IVF) successfully could be used. In this retrospective, case-control study using Swedish national registers, we compared the birth characteristics of 1206 men who have become fathers by ART with a control group consisting of age-matched men who became fathers without treatment. The differences in birth characteristics between men becoming fathers by IVF and ICSI were also assessed. For men becoming fathers by ART, OR of being born with LBW was 1.66 (95% CI = 1.17-2.36) compared with fathers who conceived without treatment. OR of being born prematurely was 1.32 (95% CI = 1.00-1.77). Men becoming fathers via ICSI had a doubled increased likelihood of being born SGA compared with men who became fathers via IVF (OR = 2.12; 95% CI = 1.17-3.83). In conclusion, we have found that men becoming fathers by ICSI treatments had more often been born SGA than men becoming fathers by conventional IVF.

The mitochondria of stallion spermatozoa are more sensitive than the plasmalemma to osmotic-induced stress: role of c-Jun N-terminal kinase (JNK) pathway.

Cryopreservation introduces extreme temperature and osmolality changes that impart lethal and sublethal effects on spermatozoa. Additionally, there is evidence that the osmotic stress induced by cryopreservation causes oxidative stress to spermatozoa. The main sources of reactive oxygen species in mammalian sperm are the mitochondria. In view of this, the aim of our study was to test whether or not osmotic stress was able to induce mitochondrial damage and to explore the osmotic tolerance of the mitochondria of stallion spermatozoa. Ejaculates from 7 stallions were subjected to osmolalities ranging from 75 to 1500 mOsm/kg, and the effect on sperm membrane integrity and mitochondrial membrane potential was studied. Additionally, the effects of changes in osmolality from hyposmotic to isosmotic and from hyperosmotic to isosmotic solutions were studied (osmotic excursions). The cellular volume of stallion spermatozoa under isosmotic conditions was 20.4 ± 0.33 µm(3). When exposed to low osmolality, the stallion spermatozoa behaved like a linear osmometer, whereas exposure to high osmolalities up to 900 mOsm/kg resulted in decreased sperm volume. Although sperm membranes were relatively resistant to changes in osmolality, mitochondrial membrane potential decreased when osmolalities were low or very high (10.7 ± 1.74 and 16.5 ± 1.70 at 75 and 150 mOsm/kg, respectively, and 13.1 ± 1.83 at 1500 mOsm/kg), whereas in isosmolar controls the percentage of stallion sperm mitochondria with a high membrane potential was 41.1 ± 1.69 (P < .01). Osmotic excursions induced greater damage than exposure of spermatozoa to a given nonphysiologic osmolality, and again the mitochondria were more prone to damage induced by osmotic excursions than was the sperm plasma membrane. In search of intracellular components that could mediate these changes, we have detected for the first time the c-Jun N-terminal kinase 1/2 in stallion spermatozoa, which are apparently involved in the regulation of the viability of these cells.