ArticlesLow male-to-female sex ratio of children born in India: national survey of 1·1 million households
Introduction
There are fewer girls than boys in India, and this sex ratio has become more skewed towards boys in recent decades; in the decennial census,1 the number of girls per 1000 boys aged 0–6 years was 962 in 1981, 945 in 1991, and 927 in 2001, and the discrepancy was more acute in urban areas (from 959 to 906 between 1981 and 2001) than in rural ones (963 to 934). The difference in sex ratio is evident by age 1 year, suggesting that fewer girls than boys are born, and widens thereafter because of the higher mortality rates in female children than in male children.2 Low sex ratios have also been recorded in other Asian countries,3 most notably China, where 847–877 girls were born for every 1000 boys in 2002.4 India has higher fertility rates than China.3 Thus, factors that lead to fewer female than male births might result in greater absolute differences in the age-specific female and male populations, especially if these factors are maintained for several decades.
There are various possible explanations for unequal sex ratios at birth, including lower caloric intake by mothers,5 Hepatitis B virus infection,6 father's occupation7 or his absence from the home,8 maternal dominance,9 smoking,10 and hormonal factors,11 time taken to conceive,12 female infanticide,13 and under-reporting of female births.14, 15 In India, there is a cultural preference for boys,2 however, and the most plausible explanation for fewer female than male births seems to be prenatal sex determination, followed by induced abortion of female fetuses.14, 16, 17, 18, 19, 20 Anecdotal evidence suggests that access to ultrasound is fairly widespread, even in rural areas,15, 21, 22 and although prenatal sex determination has been illegal since 1994 the law is often ignored.23 Self-reporting of prenatal sex determination probably results in underestimation of the problem and makes defining its role in the low sex ratio at birth of girls to boys difficult.
Our aim was to ascertain whether prenatal sex determination affects sex ratios at birth as measured by previous birth sex and to estimate the contribution of fewer female than male births to the estimated totals of so-called missing women in India.24, 25
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Survey population
In February, 1998, a survey of households in India was done to obtain a detailed fertility history of ever-married women.26 The Special Fertility and Mortality Survey (SFMS)26 was undertaken by the Office of the Registrar General of India in the sample units (or small areas) of the Sample Registration System (SRS), which is an ongoing large-scale demographic survey that provides reliable yearly estimates of fertility and mortality indicators at the national level and for major states.27 The SRS
Results
136 457 births were recorded in the SFMS, of which 133 738 are analysed here. Of these, 95 561 were second-order or higher-order births. Operational problems meant 237 units (about 3% of the population) did not complete fieldwork or data entry. The missing SRS units differed little from units included in the SFMS in sex ratios and other demographic variables. Fewer births were reported in the SFMS than in the SRS, the shortfall being higher for girls (14%, n=9950) than for boys (10%, n=7732).
Discussion
Our findings indicate that, in India, the sex of a previous child or children born affects the sex ratio of the current birth, with fewer females born as second or third children to families who have yet to have a boy. We noted similar findings with respect to the sex ratio of second-order births in rural and urban areas, irrespective of religion, and in nearly all states studied.
Differences in the numbers sampled in the SRS and SFMS, might have led to a reporting of fewer female than male
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