Re: How often do we identify fetal abnormalities during routine
third-trimester ultrasound? A systematic review and meta-analysis
Sir,
Drukker et al.1 recently reviewed the existing
literature on prevalence and types of anomalies detected in the
3rd trimester, finding that as much as 1:300
examinations led to a new diagnosis. This finding came as a reminiscence
of the first steps of the prenatal diagnosis2 and
stressed that we are not ready to dismiss the 3rdtrimester routine scan yet.
While the scaffolding of the fetus is formed by the time of the mid
pregnancy anatomy scan, during the last months of pregnancy, the fetus
grows considerably to reach its genetic determined potential, with a
process that is mostly hypertrophic, and prepares for the extrauterine
life with formation of reserves, like fat tissue deposition.
As discussed by Drukker et al., the national policies on the
3rd trimester scan are heterogeneous and the utility
of such an examination has been questioned. Traditionally, it was
oriented to identify late FGR, preventing adverse neonatal outcomes.
However, a single estimation, even with the highest achievable accuracy,
is not enough to describe the complex and dynamic process of fetal
growth3.
Re-discovering the 3rd trimester scan (30-33 weeks of
gestation) as a screening point, allows us to befit of it at its best.
Indeed, it discloses many relevant information:
- The detection of malformations not yet visible at 20 weeks, that
become evident with fetal maturation. The prime example are the
urogenital malformations, as described in the systematic review. These
malformations usually have a benign prognosis, sometimes they require
a corrective procedure and sometimes only follow up. Following the
detection of these anomalies, the expectant parents have time to be
educated on the diagnosis, to choose with the healthcare provider the
better birth setting and to plan for interventions (if indicated)
and/or for an adequate follow up.
- The detection of malformations requiring medical procedures at birth,
i.e. cardiac malformations not visible before, enabling a safe birth
and tailored life-saving interventions.
- The detection of abnormalities resulting from asymptomatic infections,
from late-presenting neurological malformations or from other
intercurrent rarer causes, such as a fetal cerebral hemorrhage. These
findings frequently carry a poor prognosis with them. A 30 weeks
diagnosis means starting a late referral pathway to prepare the
expectant parents for birth (or 3rd trimester
abortion, where legal) at best.
- The detection of FGR or a starting point of a reference curve to
detect late FRG. The evaluation of the estimate fetal weight (EFW) is
less accurate in the last weeks of gestation due to objective
difficulties in performing ultrasound measurements, hence a greater
discrepancy between fetal weight and neonatal birthweight. However,
the most relevant information we can acquire is not the fetal weight
per se but a slowed or accelerated growth curve compared to the 30
weeks screening, essential to identify higher risk pregnancies to be
monitored closely.
All these findings are detectable only in the contest of an efficient
routine screening program, preferably performed by highly trained
individuals. One of the main purposes of the Obstetrician is to reduce
as much as possible the maternal and neonatal morbidity during pregnancy
and birth, but also to give to that newborn the best possible life after
birth, including appropriate care when indicated, building tailored
follow-up pathways in-utero and after birth. Thus, the
3rd trimester routine scan is a precious arrow in our
quiver that, together with the other prenatal appointments, aims to
continuously improve our maternal and infant care.
Claudia MASSAROTTI1,2*, Chiara Roberta
GAGGERO3,4, Chiara MOLINARI4,
Diletta MARCOLIN1,2, Pierangela DE
BIASIO3,4
- Department of Neurosciences, Rehabilitation, Ophthalmology, Genetics
and Maternal and Child Health (DINOGMI dept.), University of Genoa,
Genoa, Italy
- Academic Unit of Obstetrics and Gynecology, IRCCS Ospedale Policlinico
San Martino, Genoa, Italy
- Prenatal Diagnosis and Perinatal Medicine Unit, IRCCS Ospedale
Policlinico San Martino, Genova, Italy.
- Maternal and Child Health Department, IRCCS Ospedale Policlinico San
Martino, Genova, Italy