The Role of Gender in Neonatology

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*Professor of Clinical Pediatrics/Neonatology, Department of Pediatrics, Columbia University, New York, NY **Associate Professor of Clinical Pediatrics/Neonatology, Director of Neonatology, Harlem Hospital, Columbia University,

New York, NY

I. Introduction

Evidence that differences between male and female infants in mortality, growth, and the susceptibility to specific diseases exist during the perinatal period (fetal and neonatal) has been bolstered by numerous embryologic, physiologic, epidemiologic, and anthropologic observations in humans and by laboratory studies and field observations in animals.

For a cohort of individuals at a given point in life, the sex ratio (simple ratio of males to females) depends not only on the different rates of mortality between the sexes but also on the relative numbers of males and females present at birth. In humans, as in most mammalian species, a slightly greater number of males are born than females. At birth, the sex ratio is approximately 1.05, representing a proportion of male births of about 51.3%. After birth, the mortality of males is higher, and the sex ratio declines progressively. By the end of their first year, 120 males have died for every 100 females. Males continue to die at a higher rate throughout childhood and adulthood [1-4].

Males are not only more numerous and more likely to die at birth, they are also larger. Differences in the rates of growth and metabolism between males and females have been reported from the earliest embryologic period onward and may influence sexual organogenesis, the sex ratio during gestation, and relative malefemale survival rate during intrauterine and extrauterine life [5-10].

Although these distinctions provide a useful framework for interpreting rates of mortality, they do not explain the specific male susceptibility to diseases of infancy and childhood. Males are more likely to experience stillbirth, premature birth, congenital malformations, pulmonary hemorrhage, intracranial hemorrhage, respiratory distress, perinatal asphyxia, perinatal infection, cerebral palsy, and developmental delay. Sudden Infant Death Syndrome (SIDS) is more likely to occur in males. In general, infants are at highest risk for SIDS during the first 2 to 4 months of life; other risk factors include maternal smoking, exposure to a sub-optimal uterine environment, poor fetal growth, and prematurity. Males also face a higher incidence of neurobehavioral and developmental difficulties during childhood. In epidemiologic surveys, Attention Deficit Hyperactivity Disorder (ADHD)— characterized by poor concentration ability, motoric hyperactivity, impulsivity, and, frequently, learning difficulties—is four times more common in boys than in girls. The increased male susceptibility to such diseases depends upon the interplay of environmental risk factors with fundamental genetic, endocrinologic, immunologic, and metabolic differences between the sexes [11-17].

II. The Sex Ratio During Fetal Life

A. Sex Ratio at Conception

Evidence of a preponderance of male fetal losses suggests that the sex ratio is even higher around the time of conception than at birth. By assuming a constant male-female ratio of fetal loss during pregnancy, the sex ratio from the earliest point in embryonic life has been estimated to be approximately 1:1 to 1:2. However, the precise point at which male numeric predominance develops is unknown. Several studies have shown that the ratio of Y- to X-bearing spermatozoa in humans is approximately equal; thus, the elevated sex ratio may reflect differences in rates of fertilization, implantation, or early survival. The classic explanation for the sex ratio of more rapid arrival to the ovum of lighter, faster-swimming Y-bearing spermatozoa has been discounted, and postulates involving an immunologic or hormonal preference of the ovum for Y-bearing spermatozoa remain unsupported [4,12,18-21].

An alternative explanation for male predominance is that it occurs after fertilization, at the time of implantation. Two days after fertilization, the average number of male embryos exceeds that of female embryos. At the same time, the metabolic rate, as measured by glucose and pyruvate uptake and lactate production, is higher in male embryos than female embryos. The higher metabolic rate and larger size of male embryos may confer a survival advantage (albeit temporary) on male embryos at the time of implantation [7,9,22].

B. Sex Ratios and Periconceptual Influences

Male and female fetuses and infants respond differently to biologic, environmental, and cultural influences. Environmental stresses including crowding, heat, and natural catastrophes have been found to alter the birth sex ratio in human populations. A sharp decline in the sex ratio at birth was reported 9 months following the 1995 Kobe earthquake and 320 days after the 1952 London smog and the 1965 Brisbane flood. Using combined Danish registries, Hansen etal found that severe periconceptional life events (development of cancer or myocar-dial infarction in her partner or older children) experienced by the mother during the first trimester result in a smaller proportion of male births. Temporary decreases in the sex ratio such as these might be due to alterations of parental hormones, altered quality of semen, or an increased rate of early spontaneous abortion of males. Interestingly, the proportion of males born increased sharply after both world wars in combatant

Principles of Gender-Specific Medicine

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Understanding And Treating ADHD

Understanding And Treating ADHD

Attention Deficit Disorder or ADD is a very complicated, and time and again misinterpreted, disorder. Its beginning is physiological, but it can have a multitude of consequences that come alongside with it. That apart, what is the differentiation between ADHD and ADD ADHD is the abbreviated form of Attention Deficit Hyperactive Disorder, its major indications being noticeable hyperactivity and impulsivity.

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