Study population and study design
This was a prospective observational study in women of DCDA twin
pregnancy opted for selective reduction of a co-twin in the Department
of Fetal Medicine and Prenatal Diagnosis, the Third Affiliated Hospital
of Guangzhou Medical University, China. Each woman has been previously
confirmed to carry dizygotic twin pregnancy by ultrasound, and opted for
fetal reduction due to an aneuploidy co-twin diagnosed by chorionic
villus sampling (CVS) or amniocentesis. Before reduction, each woman was
given a detailed explanation of the study, and written informed consent
of participating in this study was obtained. All women were above 18
years old, and their gestational ages were eight weeks or above at the
time of joining the study. Chromosomal abnormalities have not been found
in women and her husband, neither the couples have received a blood
transfusion, organ transplantation, cell therapy, or immunotherapy
before pregnancy. Fetal reductions were conducted by transabdominal
intracardiac injection of potassium chloride as the standard of practice
[13]. Immediately before and twice a month after reduction till
birth, the maternal blood of each woman was collected for NIPT for fetal
T21, T18, T13 to evaluate the residual cfDNA effect of the reduced
fetus. The couple’s age, gestational age at each time of blood sampling,
ultrasound scanning results, prenatal diagnosis results, and other
relevant clinical information were recorded. This study was approved by
the Ethics Committee of the Third Affiliated Hospital of Guangzhou
Medical University (no.2019096) and the Institute Review Board of
BGI-Shenzhen (BGI-IRB 19081).