Objective Assess the relationship of time to first expression after very preterm birth and mothers’ own milk quantity. Design A cohort study (nested within a randomised trial). Setting Four neonatal units in the UK. Patients 132 mothers of single or twin infants born at 23+0 to 31+6 weeks postmenstrual age. Exposures Time to the first attempt to express after birth. Primary outcomes 24-hour mother’s own milk yield on days 4, 14 and 21 after birth. Results Median time to first expression attempt was 6 hours. 51.7% expressed within 6 hours of birth (62/120) and 48.3% expressed more than 6 hours after birth (58/120). Expressing within 6 hours of birth was associated with higher milk yield on day 4 (88.3 g, 95% CI 7.1 to 169.4) and day 14 (155.7 g, 95% CI 12.2 to 299.3) but not on day 21 (73.6 g, 95% CI −91.4 to 238.7). There was an interaction between expressing frequency and time to first expression (p<0.005), with increased expressing frequency being associated with higher yield only in those who expressed within 6 hours. Expressing within 2 hours of birth was not associated with further milk yield increase. Conclusions Mothers who expressed within 6 hours of birth had higher milk yield, and a greater yield per expressing session, in the first 3 weeks after birth. This information will be highly motivating for families and the clinicians supporting them. There was no evidence of further benefit of extremely early expression (first 2 hours after birth). Trial registration number ISRCTN 16356650. Data are available upon reasonable request. A review of all requests for sharing of the study data will take place as described in National Perinatal Epidemiology Unit Standard Operating Procedures on data sharing. If agreed, any sharing of the data collected during the study must be in accordance to the Nuffield Department of Population Health and University of Oxford policies.

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极早产后极早分泌初乳是否会提高母亲的母乳量？队列研究

目的评估极早产后首次吸奶时间与母亲自身乳汁量的关系。设计队列研究（嵌套在随机试验中）。在英国设置四个新生儿病房。患者 132 名单胎或双胞胎婴儿的母亲，她们出生于月经后 23+0 至 31+6 周。出生后第一次尝试吸奶的时间。主要结果是出生后第 4、14 和 21 天的 24 小时母亲自身产奶量。结果 首次表达尝试的中位时间为 6 小时。51.7%在出生后6小时内表达(62/120)，48.3%在出生后6小时以上表达(58/120)。出生后 6 小时内吸奶与第 4 天（88.3 g，95% CI 7.1 - 169.4）和第 14 天（155.7 g，95% CI 12.2 - 299.3）较高的产奶量相关，但与第 21 天（73.6 g，95 % CI -91.4 至 238.7）。表达频率和首次表达时间之间存在交互作用（p<0.005），只有在 6 小时内表达的表达频率增加才与更高的产量相关。出生后 2 小时内吸乳与产奶量进一步增加无关。结论 产后 6 小时内吸奶的母亲在产后 3 周内的产奶量更高，每次吸奶的产奶量也更高。这些信息将极大地激励家庭和支持他们的临床医生。没有证据表明极早表达（出生后最初 2 小时）有更多益处。试用注册号 ISRCTN 16356650。可根据合理要求提供数据。将按照国家围产期流行病学单位数据共享标准操作程序中的规定对所有研究数据共享请求进行审查。如果同意，研究期间收集的数据的任何共享都必须符合纳菲尔德人口健康部和牛津大学的政策。