Division of Maternal-Fetal Medicine, Women's Health Institute, Cleveland Clinic, Cleveland, OH.
Department of Obstetrics and Gynecology, Center for Research on Reproduction and Women's Health, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA.
Am J Obstet Gynecol. 2021 Oct;225(4):417.e1-417.e10. doi: 10.1016/j.ajog.2021.04.212. Epub 2021 Apr 8.
Fetal fraction of cell-free DNA decreases with increasing maternal weight. Consequently, cell-free DNA screening for fetal aneuploidy has higher screen failures or "no call" rates in women with obesity owing to a low fetal fraction. The optimal timing of testing based on maternal weight is unknown.
This study aimed to identify the optimal timing of initial cell-free DNA testing based on maternal weight and to identify the optimal timing of repeat cell-free DNA testing in cases with an initial screen failure.
This was a retrospective cohort study of women undergoing cell-free DNA for fetal aneuploidy screening between 9 and 18 weeks through a single laboratory over 1 year from 2018 to 2019. Fetal fraction change per week was calculated, and generalized linear models were used to calculate relative risk and 95% confidence interval of a no call result at given maternal weights and gestational ages.
The vast majority of samples (99.22%) received a test result. The risk of a no call result owing to a low fetal fraction was higher with increasing maternal weight. At 9 to 12 weeks, the rate of a no call result owing to a low fetal fraction in women who weighed <150 lb was 0.14% compared with 17.39% in women weighing >400 lb. Fetal fraction increased with increasing gestational age, although the incremental increase in fetal fraction over time is inversely proportional to maternal weight. At 13 to 18 weeks' gestation, 6.45% of women weighing >400 lb received a no call result owing to a low fetal fraction. In women in the highest weight category, >400 lb, fetal fraction increased 0.5% with each week of gestation.
Although the risk of a no call result increases with maternal weight, cell-free DNA screening should be offered to all women at 9 to 12 weeks' gestation, allowing the option to have chorionic villus sampling after a positive test result. Pretest counseling for women with obesity should include the increased chance for a test failure. Most women weighing less than 400 lb will receive a test result and more than 80% of women with a weight of >400 lb will receive a test result at 9 to 12 weeks' gestation. Data regarding the expected increase in cell-free DNA fetal fraction per week may help guide the timing of a redraw to optimize test success.
游离胎儿 DNA 的胎儿分数随着母亲体重的增加而降低。因此，由于胎儿分数低，肥胖女性的游离胎儿 DNA 筛查出现更高的筛查失败率或“无结果”。基于体重的最佳检测时机尚不清楚。
本研究旨在确定基于母体体重的初始游离 DNA 检测的最佳时机，并确定初始筛查失败时重复游离 DNA 检测的最佳时机。
这是一项回顾性队列研究，纳入了 2018 年至 2019 年间在一家实验室接受游离胎儿非整倍体筛查的 9 至 18 周的孕妇，共 1 年。计算每周游离胎儿分数的变化，使用广义线性模型计算特定体重和孕龄下无结果的相对风险和 95%置信区间。
绝大多数样本（99.22%）获得了检测结果。由于胎儿分数低导致无结果的风险随着母亲体重的增加而增加。在 9 至 12 周时，体重<150 磅的女性由于胎儿分数低导致无结果的比例为 0.14%，而体重>400 磅的女性为 17.39%。胎儿分数随着孕周的增加而增加，尽管随着时间的推移，胎儿分数的增量增加与母亲体重成反比。在 13 至 18 周时，体重>400 磅的 6.45%女性由于胎儿分数低导致无结果。在体重最高的>400 磅女性中，每增加一周妊娠，胎儿分数增加 0.5%。
尽管无结果的风险随着母亲体重的增加而增加，但所有孕妇均应在 9 至 12 周时进行游离 DNA 筛查，以便在阳性检测结果后选择绒毛膜绒毛取样。对于肥胖女性的术前咨询应包括检测失败的几率增加。体重<400 磅的大多数女性将获得检测结果，体重>400 磅的女性中有 80%以上将在 9 至 12 周时获得检测结果。关于每周游离胎儿 DNA 胎儿分数预期增加的数据可能有助于指导重新绘制的时机，以优化检测结果。
