To explore occurrence of chromosomal abnormality in fetuses with increased nuchal translucency (NT) thickness at first trimester.

From January 2016 to January 2019, a total of 1 261 fetuses with increased NT(≥3.0 mm) thickness at first trimester were selected as research subjects. Their case data were analyzed retrospectively. According to results of ultrasonic diagnosis of fetus, they were divided into isolated group (n=1 017, fetus with increased NT thickness only) and combined group (n=244, fetus with increased NT thickness and others structural malformation). Among them, there were 1 164 fetus who received interventional prenatal diagnosis to identify occurrence of fetus with chromosomal abnormalities or not. According to isolated group and combined group they belonged to, they were divided into isolated subgroup (n=965) and combined subgroup (n=199). Chi-square test were used to compare differences of incidence of fetus chromosomal abnormalities between isolated subgroup and combined subgroup, also between these two subgroups in different levels of NT thickness. The procedure followed in this study was consistent with World Medical Association Declaration of Helsinki revised in 2013.

① The top three of others ultrasonic structural malformations which combined in combined group of 244 fetuses were 45 cases (18.4%) of cystic hygroma, 44 cases (18.0%) of heart malformations and 23 cases (9.4%) of exomphalos. ② For cases who received interventional prenatal diagnosis, the incidence of chromosomal abnormality in combined subgroup was 52.8% (105/199), which was significantly higher than that of 16.9% (163/965) in isolated subgroup, and the differences was statistically significant (χ²=123.900, P<0.001). ③ For cases who received interventional prenatal diagnosis, when NT values were 3.0-3.9 mm, 4.0-4.9 mm, 5.0-5.9 mm, ≥6.0 mm, the incidence of chromosomal abnormality in combined subgroup were 34.8%, 60.9%, 56.3%, 67.3%, which were significantly higher than those of 10.8%, 20.9%, 31.4%, 42.9% in isolated subgroup, and the differences were statistically significant (χ²=31.400, P<0.001; χ²=29.453, P<0.001; χ²=5.676, P=0.028; χ²=6.854, P=0.014).

The fetus is at greater risk of chromosomal abnormality when it is with increased NT thickness combined with others structural malformations, or with NT value ≥6.0 mm at first trimester. Once fetus with increased NT thickness is found at first trimester, their heart structure screening should be taken.