To analyze the indications for invasive prenatal diagnosis in the third trimester and summarize the pregnant outcome.

Clinical data of 121 women who underwent invasive prenatal diagnosis in the third trimester in the prenatal diagnostic center of the First Medical Center of Chinese PLA General Hospital from January 2016 to December 2020 was retrospectively analyzed. Different genetic diagnostic methods were used according to different indications. Indications and results of prenatal diagnosis, as well as the complications within two weeks after the invasive procedure, pregnancy outcome, and neonatal follow-up of all the participants were described.

Among the 121 cases, 107 cases underwent amniocentesis, seven underwent percutaneous umbilical blood sampling, and seven had both procedures performed at the same time (one underwent thoracocentesis at the same time). Newly identified ultrasound abnormalities in the second and third trimesters were the main indications for prenatal diagnosis, accounting for 99.2%(120/121), of which short limbs and fetal growth restriction accounted for 25.0% (30/120) and 20.0% (24/120), respectively. Genetic abnormalities and congenital diseases were detected in 20 cases with a detection rate of 16.5%(20/121). Among them, there were nine cases of achondroplasia, five cases of pathogenic copy number variations, one case of achondroplasia with pathogenic copy number variation, one trisomy 18, one 47,XXX, one tetrasome mosaicism of 12p, one de novo WTX c. 1072(Exon2) C>Tp.R358X heterozygous mutation, and one fetal hypoproteinemia. In addition, six cases with copy number variation of unknown significance (VUS) were detected, noting for a detection rate of 5.0%(6/121). Among the 20 cases with abnormal detection, 15 were terminated, two delivered prematurely before obtaining the prenatal diagnosis results, one underwent cesarean section before obtaining prenatal diagnostic results and two continued the pregnancies. In the six cases with VUS, one was terminated and the other five continued the pregnancy. Only one case had preterm premature rupture of membranes 2 d after amniocentesis and the incidence rate of complications after all kinds of invasive procedures was 0.8% (1/121). During the neonatal follow-up, postnatal whole exome sequencing revealed monogenetic disorder in two cases with normal prenatal diagnostic results; the patient with 12p chimerism had developmental delay; the one with WTX mutation deceased on the day of born; the rest newborns developed normally.

As a relatively safe method, invasive prenatal diagnosis in the third trimester is of great importance and value in reducing the miss diagnostic rate of fetuses with severe genetic diseases and birth defects. The appropriate application of prenatal whole exome sequencing could further help to decrease the miss diagnostic rate of monogenetic disorder.

Prenatal diagnosis; Pregnancy trimester, third; Whole exome sequencing; Pregnancy outcome; Microarray analysis; Polymorphism, single nucleotide