Son preference prevails widely in South and East Asia and is demonstrated by sex-selection methods such as differential stopping and sex-selective abortion. Differential birth-spacing is another possible way by which this disproportionate desire for sons could manifest itself. The time span before moving on to the next pregnancy may be short as long as sons have not been born. Shorter birth spacing leads to higher demand on the mother's body, leading to higher health risk to both mother and child. In addition there is greater competition among siblings for parental care and resources. In this study, we examine this phenomenon by using three demographic and health surveys of Pakistani households covering the period from 1990-91 to 2012-13 and carrying out a set of duration model estimations. We investigate if and how preference for sons affects birth-spacing, if this relationship has evolved over time, if it depends on the order, number or overall proportion of sons born,and whether it increases the probability of risky births (those less than 24 or 18 months from the previous birth). We gauge the type of households in which this phenomenon appears to be more prevalent. We find strong evidence for differential behaviour at early parities throughout the period. Women whose first or second children are sons have significantly longer subsequent birth intervals compared with women with no sons. Birth-spacing differs substantially by parity and number of children. Sex of the firstborn is another significant factor. The association seems to have undergone little significant change over the past two decades. Besides, the likelihood of risky births is higher among women without one or more sons. This phenomenon of gender-specific lengthy and risky birth intervals is prevalent more among households that are wealthier or nuclear and among women with greater say in intra-household decisions.

中文翻译：

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巴基斯坦对男孩的偏好和生育间隔的长度

重男轻女在南亚和东亚普遍盛行，这体现在性别选择方法上，例如差异停止和性别选择性流产。不同的生育间隔是另一种可能表现出这种对儿子不成比例的渴望的方式。只要儿子还没有出生，进行下一次怀孕之前的时间跨度可能很短。更短的生育间隔导致对母亲身体的更高需求，从而导致母婴健康风险更高。此外，兄弟姐妹之间在父母照顾和资源方面的竞争更加激烈。在本研究中，我们通过使用涵盖 1990-91 年至 2012-13 年期间的三项巴基斯坦家庭人口和健康调查并进行一组持续时间模型估计来检验这一现象。我们调查了对儿子的偏好是否以及如何影响生育间隔，这种关系是否随着时间的推移而演变，是否取决于儿子出生的顺序、数量或总体比例，以及它是否会增加风险生育的可能性（小于 24或前一次出生后 18 个月）。我们评估了这种现象似乎更普遍的家庭类型。我们发现了整个时期早期胎次不同行为的有力证据。与没有儿子的妇女相比，第一个或第二个孩子是儿子的妇女的生育间隔明显更长。生育间隔因胎次和儿童数量而有很大差异。长子的性别是另一个重要因素。在过去的二十年里，该协会似乎几乎没有发生什么重大变化。除了，在没有一个或多个儿子的妇女中，风险分娩的可能性更高。这种因性别而异的漫长而危险的生育间隔现象在较富裕或有核的家庭中以及在家庭内部决策中有更大发言权的妇女中更为普遍。