4.DISCUSSION
In this study, we mainly found that UA velocities were decreased with
the severity of growth restriction and the UA-TAMXV was independent
predicting factor of FGR. To our knowledge, this is the first study to
assess associations between the UA velocities and growth disorders.
In this study, the absolute UA velocities is decreased with the severity
of growth restriction, that’s to say, it is decreased in SGA group and
further decreased in FGR group when compared with AGA group at 37 weeks,
suggesting that the absolute UA velocities was associated with the
feto-placental blood flow. As all of the fetuses enrolled in our study
presented normal UA Doppler spectrums, our finding suggested that UA
velocities, particularly UA-TAMXV and UA-PSV, might be more predictive
of late-onset FGR and SGA than the conventional UA Doppler parameters,
such as UA-PI and UA-S/D.
Previous studies have shown that abnormal fetal
middle
cerebral artery may occur in 20% of term SGA fetuses
with
normal UA Doppler results18
19. It has certain value for clinical
management of FGR20,
however, its role in predicting FGR with normal UA Doppler spectrums
remains unclear. As described in previous studies, the placental volume
blood flow could also be assessed by the umbilical venous
velocities21
22. However, the umbilical venous
velocities were prone to errors and still need to be
standardized23. One
longitudinal study demonstrated that the UA-TAMXV was best correlated
with the umbilical vein volume blood
flow14. Our study
showed that UA-TAMXV was decreased in the FGR and was consistent with
previous studies. In routine ultrasound examination, as the UA
circulation Doppler has been generally used to assess the feto-placental
blood circulation, the UA velocities can be easier and quicker to
acquire than the umbilical vein velocities. As we know, when the
placental blood flow resistance increases, the end diastolic blood flow
decreases. Therefore, the UA-EDV might be absent and cannot be detected
in severely growth-restricted fetuses, whereas the UA-TAMXV can still be
readily detected in this condition. Our findings suggested that the
UA-TAMXV might be of predictive value for the FGR. Therefore, the
UA-TAMXV might be a more preferred parameter for evaluating the placenta
volume blood flow as well as the degree of fetal ischemia.
Previously studies reported that fetal growth disorders are associated
with an increased risk of
APOs2
3. Unfortunately, no obvious APOs were
found in our study. The possible might be as follows. Firstly, this
negative finding may be related to the small sample size. Furthermore,
all of the fetuses in our study had normal UA Doppler spectrums, which
indicates that the fetus was not seriously compromised. Lastly, the
timing for delivering in SGA fetus is at 37 weeks or so rather than
terminating the pregnancy until the fetus is severely damaged. A large
study reported a significantly increased risk of fetal death in SGA
delivered >37 weeks compared to those delivered at 37
weeks24. Another study
including 92,218 singletons found that the fetal death rates were lower
in detected than those in undetected
FGR2. It follows then
that the key to preventing APOs is detection of FGR and timely delivery.
Nevertheless, further researches with more cases are required to observe
the relationships among the UA velocities, FGR with advanced GA and
APOs.
It was showed that the maternal height was significantly and inversely
associated with risk of SGA25. A previous
reporting suggested that the maternal height was a stronger predictor of
birth weight than
ethnicity26. Consistent
with previous studies25
26, the maternal height of SGA was
shortest among the three groups, and was independently predictive of SGA
rather than FGR in our study. Conversely, the UA-TAMXV was independently
predictive of FGR rather than the maternal height. We speculated that
the maternal height was more closely associated with SGA, whereas the
UA-TAMXV was more closely related to FGR. Therefore, UA-TAMXV could
figure out FGR from SGA
when
the women were at the same maternal height.
There are some limitations in our study. Firstly, most pregnancies with
SGA and FGR were transferred from other hospitals, so it was not always
possible to collect actual primary UA Doppler spectrums and serial data.
Secondly, as this was a retrospective study, the retrospective design
can lead to an inherent risk of selection bias. Lastly, because all of
fetuses were delivered at about 37 weeks’ gestation, the pregnancy
outcome assessment could not be objectively assessed.
In
conclusion,
the
UA velocities were decreased with the severity of growth restriction and
the UA-TAMXV was independently predictive of FGR. The results suggested
that the UA-TAMXV might be a new parameter to predict FGR, which might
provide a theoretical basis for earlier prediction and better management
FGR as well as distinguishing FGR from SGA. Moreover, it might help to
determine the optimum time for surgical intervention as well as to
select those pregnancies which are in need of close monitoring. However,
further studies are needed to confirm these questions.