Screening for trisomy 21 during the routine second‐trimester ultrasound examination in an unselected Chilean population

Abstract

ABSTRACT

Prenatal diagnosis of chromosomal abnormalities in a resource‐poor setting

“…This finding agrees with other reports [4,8] although their methods of risk estimation were different, but the improvement seen in our study could have been greater if more first-trimester examinations had been included, as well as transvaginal examinations [19]. Our incremental detection by ultrasound screening was better than the use of likelihood ratios in a higher-risk cohort [18], in which a 36% improvement was accompanied by a significant reduction in false positives.…”

“…The high sensitivity of ultrasound screening for detecting autosomal trisomies noted in this study concurred with published findings concerning high-risk pregnancies [13,14,16] or reported by specialized centers [18]. The sensitivity of ultrasound-based risk adjustment was higher in this study than in population-based studies [4,8,19], low-risk cohort studies [20,21], or studies relying on clinical suspicion before referral [22], and the difference was expected from the disparities in study design, patient selection, and modes of ascertainment.…”

“…We noted, as have others [14,18,19,21,22,24], that normal features or isolated soft markers were uncommon on ultrasound when karyotypic abnormalities were severe. A recent review [8] corroborates the limited contribution of isolated soft markers in our study but is in contradiction with reports of a more than 20% incidence in trisomy 21 detected with soft markers [12,14,16].…”

“…The indications for ultrasound assessment were the following: a high obstetric risk necessitating prenatal care at the hospital (2 scans, in weeks 11-14 and 18-24); genetic counseling because of age (N 36 years at conception) or because of a fetal risk of abnormality (1 or 2 scans, in weeks 11-14 and/or [16][17][18][19][20][21][22][23][24]; or an emergency referral because of an abnormal clinical course or abnormal findings on a basic scan offered before the 24th week at the primary care level.…”

“…The risk of aneuploidy was then assessed according to an algorithm combining maternal age and likelihood ratios for a variety of ultrasound findings [18]. An absence of positive findings after 17 weeks signified a reduced risk.…”