Study design and data collection
We conducted a retrospective cohort study of all twin pregnancies
undergoing cfDNA screening for aneuploidy and delivered at International
Peace Maternity and Child Health Hospital in Shanghai, China between
January 2018 to December 2021. All women with twin pregnancies were
offered a scan to determine chorionicity as well as first-trimester
nuchal translucency (NT) at
11+0-13+6 weeks. Dichorionic was
confirmed when ultrasound assessment clearly indicates two placentas.
The twin peak sign is used to distinguish chorionicity if only one
placenta is visualized. Following this, a thorough genetic consultation
was offered to all future parents of the twin cohort. The
characteristics of the tests and potential advantages and disadvantages
of the different modalities of prenatal genetic testing will be
discussed. Parents will also be informed that NIPT included information
on the test being validated for the detection of only T21, T18 and T13,
and the evidence of using NIPT in twin pregnancy is less than it is in
singletons,thus offering limited information compared with invasive
diagnostic testing. We used two platforms for cfDNA-BGI-Health
(Shenzhen, China) and Berry Genomics. The screening was performed
specific to the clinical site.
We abstracted maternal demographic characteristics, fetal fraction,
obstetric outcomes, and neonatal outcomes from the medical
record,including maternal age, race, parity, education levels,
pre-pregnancy body mass index (BMI), method of conception, smoking
status, gestational age delivery, and neonatal birthweight. Birth
discordant was defined as an inter-twin EFW discordance greater than
20%. sFGR was defined as a condition in which the EFW of one twin is
less than the 10th centile and an inter-twin EFW discordance greater
than 25%. Cases with chromosome abnormalities were excluded from this
study.
The exclusion criteria were the presence of twin-to-twin transfusion
syndrome (TTTS), monoamniotic twins, twin anemia–polycythemia sequence
(TAPS), and congenital, structural or genetic malformations in the
fetus. To assure the placentas would be intact, only MC twins gestations
delivered through cesarean section were included to ensure an intact
placenta.
The
Quintero criteria were used to diagnose TTTS, while TAPS was diagnosed
based on a postnatal inter-twin hemoglobin difference of over 8 g/dL.
Monochorionic twin pregnancies were identified in the first or early
second trimester through ultrasonographic criteria, including the
presence of a single placenta, a thin dividing membrane, and the absence
of a twin peak (lambda) sign. Obstetricians confirmed monochorionicity
through postpartum examination of the placenta, which showed a single
placenta with inter-twin
anastomoses[4].
Selective fetal growth restriction (sFGR) was characterized by two
criteria: (I) a birth weight discordance of more than 25% and (II) the
presence of an FGR twin with a birth weight below the 10th percentile.
The calculation for birth weight discordance involved subtracting the
weight of the FGR twin from the weight of the
appropriate-for-gestational-age (AGA) twin, dividing that difference by
the weight of the larger twin, and multiplying the result by
100%[4,
10].
This study was approved by the Ethics Review Board of the International
Peace Maternity and Child Health Hospital Affiliated to the Shanghai
Jiao Tong University School of Medicine (No.GKLW2019-20).