PubMed · 14684656
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Ian Forgacs. 2003-12-20. Referee's half-time analysis.. https://doi.org/10.1136/bmj.327.7429.1474
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The prevalence of male homosexuality probably varies over time and across societies. One reason for this variation may be the joint effect of two factors: (1) variations in fertility rate or family size; and (2) the fraternal birth order effect, the finding that the odds of male homosexuality increases with each additional older brother. Because of these effects, the rate of male homosexuality may be relatively high (at least in terms of sexual attraction if not behavior) in societies that have a high fertility rate, but this rate has probably declined somewhat in some, particularly western, societies. Thus, even if accurately measured in one country at one time, the rate of male homosexuality is subject to change and is not generalizable over time or across societies.
The increased mortality and morbidity rates in multiple-gestation neonates are not completely understood. Troponin measurements have a role in situations where the evaluation of the cardiac damage is difficult, such as in cases of unexplained intrauterine fetal growth restriction or death. These conditions, along with perinatal hypoxic risk and in utero ischemic damage, are frequently found in multiple gestations. In this context, a myocardial damage could be expected more frequently in multiple than in singleton births. We hypothesized that cord blood cardiac troponin T and troponin I, markers of myocardial damage, could be different between singleton and multiple pregnancies and, among twins, between the first- and the second-born twin. Troponins T and I and creatine kinase MB concentrations were not increased in twins at birth and were not different between the first- and the second-born twin. These data suggest that myocardial damage, evaluated by cardiac troponin T, troponin I, and creatine kinase MB measurements, does not seem to be a relevant problem in multiple-gestation neonates.
OBJECTIVE: The purpose of this study was to determine gestational age-specific incidence and risk factors of respiratory distress syndrome (RDS) in twins compared with singletons. STUDY DESIGN: An analysis of 850,406 singleton and 23,278 twin infants born alive in Finland between 1987 and 2000 was performed. A number of antenatal and perinatal/intranatal factors were evaluated. RESULTS: At less than 28 weeks of gestation, the incidence of RDS was higher in both first- and second-born twins compared with singletons. At more advanced gestation, first-born twins had a significantly lower incidence of RDS compared with the others. There was no difference in the concordance of RDS between same-sex and opposite-sex twin pairs. Vaginal delivery, female sex, being born first, and being the lighter of the twins protected from RDS. CONCLUSION: After taking into account gestation, twins are not at higher risk of RDS compared with singletons except at very early gestation. Environmental factors predominate over genetic ones in the predisposition to RDS in twins.