Gestational age is one of the most important features of a pregnancy when making clinical decisions. In particular, the management of delivery, such as the timing of a caesarean section before labour or when to induce labour, is crucially informed by knowledge of gestational age. Overestimation of gestational age could lead to iatrogenic premature birth, whereas underestimation of gestational age could increase the risk of post-term stillbirth. Consequently, most pregnant women in high-income countries are offered an ultrasound scan at the end of the first trimester, when gestational age can most accurately be assessed by measuring the crown-rump length (CRL). Delivering this service necessitates women being identified as pregnant at an early stage and being appropriately referred, and that ultrasound is available to all pregnant women in the first trimester. Obstacles to the delivery of this service include geographical, economical, and societal issues, and the capacity of health-care services. These obstacles are common and frequently coexist in low-income countries. Consequently, many women will present for clinical care in late pregnancy and without having undergone gestational age dating by ultrasound in the first half of pregnancy. For example, one study showed that only 29% of women in Uganda had their first antenatal care visit during the first trimester.

中文翻译：

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在低收入国家中，超声对妊娠晚期妊娠胎龄的估计：是衡量还是现成的？

妊娠年龄是做出临床决定时怀孕的最重要特征之一。特别是，分娩的管理，例如分娩前或何时引产的剖腹产时机，关键在于了解胎龄。高估胎龄可能导致医源性早产，而低估胎龄可能增加早产的风险。因此，在高收入国家/地区中，大多数孕妇在孕早期会接受超声检查，此时可以通过测量冠臀长（CRL）来最准确地评估胎龄。提供这项服务需要使妇女在早期被确定为怀孕并得到适当的介绍，而且在孕早期，所有孕妇都可以使用超声波检查。提供此项服务的障碍包括地理，经济和社会问题以及医疗服务的能力。这些障碍在低收入国家很常见，并经常并存。因此，许多妇女将在怀孕后期就诊，并且在怀孕的前半段没有经过超声对胎龄的约会。例如，一项研究表明，乌干达只有29％的妇女在头三个月进行了第一次产前检查。许多妇女将在妊娠晚期就诊，并且在妊娠的前半段没有经过超声波对胎龄的约会。例如，一项研究表明，乌干达只有29％的妇女在头三个月进行了第一次产前检查。许多妇女将在妊娠晚期就诊，并且在妊娠的前半段没有经过超声波对胎龄的约会。例如，一项研究表明，乌干达只有29％的妇女在头三个月进行了第一次产前检查。