Prenatal diagnosis of fetal malformations in a maternity Level 3: about 100 cases

Background:

Birth defects are a social, economic and psychological heavy. However, the technical progress to explorations in utero improves the prognosis of deformities. Ultrasonography remains the golden standard for the detection of various abnormalities.

Objective:

The aim of our study was to evaluate the experience of obstetrics gynecology department in the diagnosis of congenital malformations and compare the results with the literature to draw conclusions for improving the prognosis of these malformations.

Methods:

This was a retrospective, descriptive study including 100 cases of fetal malformations followed in the center of maternity and neonatology of Tunis, collected over 28 months between January 2013 and April 2015. The study included cases with ultrasound discovery of defects during prenatal care.

Results:

For maternal characteristics, the mean age was 31.88 years.

The mean gravidity was 2.38 and the average parity was 1, 46. The inbreeding was 18%. The medium-term discovery of anomalies was 25SA 3 d, with 17% in the first quarter, 54% in the second quarter and 29% in the third quarter.

A further exploration was needed for imaging limitations of ultrasound. What to do depends on the type and term of the diagnosis of malformation.

The first-trimester detection rate for major CNS anomalies was 46%. All fetuses presenting with acrania/exencephaly (3cases) and encephalocele (one case) were diagnosed during the first trimester. Furthermore, the detection rates for hydrocephaly (14cases) and spina bifida (5cases), were diagnosed in the first (50% of spina bifida cases) or second (50% of hydrocephalus cases) trimesters. Agenesis of corpus callosum and microcephaly cannot be detected in the first trimester, and were usually observed during the third trimester.

A 14% (14/100) detection rate for major cardiac defects was achieved during the first trimester. High detection rates were achieved for hypoplastic left heart syndrome (HLHS) and for atrioventricular (AV) canal and right heart defects. In contrast, detection rates were low for transposition of the great arteries and for AV block.

Seventy-two per cent of digestive and abdominal wall defects were detected in the first trimester: omphalocele and gastroschisis. Urinary tract obstruction, appearing as megacystis, achieved a detection rate of 85%, cystic kidneys had a detection rate of 22% and hydronephrosis had a detection rate of 4%.

The medical termination was indicated in 42% of cases. Misoprostol was the molecule of choice with 10% of cases with complications.

The review foetopathologique was made in 31% of cases, having consolidated the ultrasound abnormalities and describe others no detected by ultrasound to determine the risk of recurrence couples for a possible genetic counseling.

Discussion:

Our study demonstrated that the first-trimester ultrasound performed at 11 – 14 weeks was able to detect 17% of major structural anomalies in chromosomally normal fetuses in singleton pregnancies. The rates of later diagnosis of these defects in the second and third trimesters, were 54% and 29%, respectively. As expected, the highest detection rates were found for acrania, holoprosencephaly, omphalocele, gastroschisis and megacystis. Reported series, however, showed a remarkable variability in detection, given that the rates ranged from 18% to 71%. The two main factors accounting for a major part of this variability were differences in the inclusion criteria for anomalies and in the type and length of postnatal follow up. An earlier prenatal diagnosis of major fetal anomalies may result in some advantages in management, such as: (a) the possibility of scheduling additional examinations well before the limits for legal termination; (b) the option for an earlier and safer termination of pregnancy; and (c) earlier reassurance and reduced anxiety.

Furthermore, it appears that women prefer earlier screening, when possible. Recently, it has been described that the vast majority (83%) of omphaloceles containing only bowel and observed at 11 – 13 weeks, resolve by 20 weeks30. Moderate megacystis (7 – 15-mm bladder length) seen in normal-karyotype fetuses deserves further evaluation given that it is associated with a 90% chance of resolution and a favorable prognosis. Cystic hygroma is a well-established entity in the second trimester, but it is a confusing finding in the first trimester because the distinction between cystic hygroma and an increased NT is rather subjective, as shown by frequencies varying from 0% (0/29) to 33% (10/30) in reported series. The latter show higher early overall detection rates, as all hygromas are considered to be diagnosed in the first trimester.

Some weaknesses of our study should be pointed out. The first is the mixed study population, which included routine prenatal patients together with those referred because of an increased NT, a positive screen for aneuploidy, or even for a suspected structural anomaly. Although it is well known that it is easier to detect anomalies in a high-risk population, such as fetuses with increased NT, referrals accounted for only 13% of the study population and for 23% of the abnormal fetuses. The second weakness was the fact that these first-trimester ultrasound scans were performed by highly trained individuals using top-quality equipment at a tertiary center, and that less-experienced clinicians may not be able to replicate our results. The third weakness is that some pregnancies had their second- and third-trimester scans performed in another center. Another limitation is that early fetal echocardiography during the last decade has usually been performed at 14 – 16 weeks and therefore some cardiac defects detected in the first trimester were ultimately diagnosed in the 16th week. And, finally, the poor detection of minor abnormalities also deserves attention, although this was not the main goal of the fetal anatomic survey.

Conclusion:

The antenatal diagnosis of malformations is usually done at the end of the second quarter, judged late compared to literature. Qualified staff, good quality ultrasound systems, and a multidisciplinary approach are needed to improve the timeliness of diagnosis. Furthermore, the management often poses a problem of medical ethics requiring the use of a bioethics committee.