UConn Health, Framingham, Connecticut; Natera, Inc, San Carlos, California; and Virtua Health, Voorhees, New Jersey.
Obstet Gynecol. 2018 Aug;132(2):428-435. doi: 10.1097/AOG.0000000000002728.
Noninvasive prenatal testing (NIPT) sometimes fails to provide a test result, usually as a result of low cell-free DNA fetal fraction. We investigated how initial fetal fraction, maternal weight, gestational age, and time between blood sampling contribute to obtaining an informative result when a redraw is performed.
We performed a retrospective data review of NIPT samples received between January and October 2016 by a commercial laboratory, where the initial blood draw did not yield a result and a second sample was drawn between 5 and 28 days after the initial sampling. We included cases with fetal fraction less than 2.8% (the threshold for "no result" in this laboratory) and those with higher fetal fraction but where the NIPT results could not be interpreted with high confidence.
For 4,018 cases in which a redraw was recommended, a result was obtained for the second sample in 2,835 cases (70.6%) (95% CI 69.1-72.0%). For the 2,959 cases with insufficient fetal fraction, there was a result for the second sample in 1,861 cases (62.9%) (95% CI 61.1-64.6%). For this subset, the average increase in fetal fraction was 1.2% with an average interval between draws of 14 days. Informative redraw rate was strongly dependent on maternal weight and fetal fraction measured at the first draw. Gestational age was not an important determinant. Informative redraw rate increased rapidly over the first 8 days after the initial draw and more slowly thereafter.
Based on fetal fraction in the initial sample, maternal weight, and interval between blood draws, women can be provided with a personalized estimate of their likelihood of a result on redraw. This should aid in the counseling of women faced with the choice of reattempting NIPT, conventional screening, or an invasive diagnostic test.
非侵入性产前检测（NIPT）有时无法提供检测结果，通常是由于游离胎儿 DNA 分数较低所致。我们研究了当重新采血时，初始胎儿分数、产妇体重、妊娠龄和两次采血之间的时间如何有助于获得有意义的结果。
我们对一家商业实验室在 2016 年 1 月至 10 月间收到的 NIPT 样本进行了回顾性数据分析，这些初始血样未得出结果，且在初次采血后 5 至 28 天之间采集了第二份血样。我们纳入了胎儿分数小于 2.8%（本实验室“无结果”的阈值）的病例，以及那些胎儿分数较高但无法进行高可信度解读的病例。
在建议进行重新采血的 4018 例病例中，有 2835 例（70.6%）（95%CI 69.1-72.0%）获得了第二份血样的结果。在 2959 例胎儿分数不足的病例中，有 1861 例（62.9%）（95%CI 61.1-64.6%）获得了第二份血样的结果。对于这部分病例，平均胎儿分数增加了 1.2%，两次采血之间的平均间隔为 14 天。有意义的重新采血率与初次采血时的产妇体重和胎儿分数密切相关。妊娠龄不是一个重要的决定因素。有意义的重新采血率在初始采血后 8 天内迅速增加，此后增加速度较慢。
根据初始样本中的胎儿分数、产妇体重和采血间隔，可向女性提供其重新采血时获得结果的可能性的个性化估计。这将有助于为面临重新尝试 NIPT、常规筛查或有创性诊断性检查的女性提供咨询。
