Introduction
In recent years, there has been a significant rise in twin pregnancies
due to the advancements in assisted reproductive technologies. However,
these pregnancies are more susceptible to complications such as fetal
growth restriction (FGR), premature birth, and perinatal loss. Twin
pregnancies can also experience selective fetal growth restriction
(sFGR), where one twin is compromised while the other grows normally.
This condition puts the affected twins at a higher risk of perinatal
mortality and
morbidity[1].
Additionally, compared to non-sFGR pregnancies, those with sFGR tend to
have earlier deliveries and higher rates of neonatal unit
admission[2].
It is estimated that 10-20% of twin pregnancies are affected by sFGR.
Monochorionic twins have a higher incidence rate of 19.7% compared to
dichorionic twins at
10.5%[3]. According
to the latest guidelines from the International Society of Ultrasound in
Obstetrics and Gynecology (ISUOG), sFGR is characterized by an estimated
fetal weight (EFW) below the 10th percentile in one twin and an
inter-twin EFW discordance of over 25%. Additionally, a discordance
threshold of 20% may be used to identify pregnancies with a higher
likelihood of negative
outcomes[4].
Detecting pregnancies at risk of sFGR or birth weight discordance in the
early stages can enhance counseling, intervention timing, and
potentially enable preventive treatment trials. Various parameters
identified during early pregnancy have been linked to the development of
sFGR later in pregnancy. Although abnormal cord insertion is associated
with sFGR in twins, it is present in more than 55% of all twin
pregnancies[5]. A
particularly isolated screening test is urgently needed in clinical
practice.
Placental pathology often correlates with the onset and prognosis of
sFGR. In cases of MC twins, sFGR is believed to be the result of an
unequal distribution of blood through placental anastomoses due to
uneven sharing of the
placenta[6], whereas
in DC twins, from placental insufficiency in one of the
placentas[7].
Throughout gestation, the villous trophoblast in the placenta
experiences ongoing turnover, which leads to the release of apoptotic
debris and cell-free DNA (cfDNA) into the maternal bloodstream. Research
suggests that levels of cfDNA may also indicate placental issues. The
amount of cfDNA specifically from the fetus is known as fetal fraction,
and it has been associated with negative perinatal outcomes, including
FGR in single
pregnancies[8,
9]. Here, we testing the hypothesis
that the fetal fraction in twin pregnancy would reflect birthweight
discrepancy.