Shama Munim  ( Department of Obstetrics and Gynecology, Aga Khan University Hospital, Karachi. )
Salva Nadeem  ( Department of Obstetrics and Gynecology, Aga Khan University Hospital, Karachi. )
Nadya Ali Khuwaja  ( Department of Obstetrics and Gynecology, Aga Khan University Hospital, Karachi. )

Congenital anomalies occur in 2-3% of all births. They are an important cause of Perinatal morbidity and mortality and account for 20-30% of perinatal deaths.1-4 Survivors have mental and physical disability. The psychological trauma and cost associated with foetal abnormalities, has lead to use of ultrasound for the prenatal diagnosis as an essential part of antenatal care.4

The diagnostic ability of ultrasound is well established by a number of studies.5-7 Detection of foetal abnormalities depends on a number of factors including the nature or type of abnormality, sophistication of equipment and experience of operator. The Prevalence of abnormalities also depends upon the population being scanned. Therefore congenital abnormalities are higher among the referral center population as compared to the general population.4

In Pakistan where the social support system is virtually non-existent, bringing up a child with mental or physical handicap is a major burden for the parents and family. Primary prevention with Folic acid for this purpose has a limited role. In cases where primary prevention does not seem possible, prenatal diagnosis by ultrasound scan provides the next best alternative. The purpose of this study was to describe the trends of congenital abnormalities seen at a tertiary care facility in Karachi.

This study presents the experience at the Aga Khan University Hospital, Karachi, Pakistan from January 2001- December 2003. This is a tertiary care teaching hospital of private sector in Karachi, equipped with latest diagnostic and therapeutic facilities. About a third of patients attending the department of Obstetrics and Gynaecology are high risk pregnancies. It is the practice in our department to offer two ultrasounds during pregnancy one before 12 weeks and the other at 20 weeks.

Congenital anomalies were defined as structural defects, chromosomal abnormalities, inborn error of metabolism or rare genetic syndromes, diagnosed either prior to or after birth. Minor abnormalities like hypospadias, skin tags, and low set ears have been excluded from the study.

Physicians performing ultrasound vary from those with limited experience doing a level scan to those experienced performing level three ultrasound. About a quarter of these examinations are also performed by Sonologists and Radiologists outside our University Hospital. In cases where abnormalities were diagnosed antenatally a repeat scan was performed at the Foetal Medicine Unit in the department of Obstetrics and Gynaecology.

All cases complicated by congenital abnormalities served as the study population. This data was gathered from various sources, that include congenital anomaly register, and hospital records of all live births and from the TOP, (Termination of pregnancy register) of all those undergoing termination of pregnancy for foetal abnormalities. Examination of the newborn/abortus comprised of clinical examinations, Radiological studies and chromosomal analysis if necessary.

The demographic detail of study subjects was noted. In addition, types of birth defect, sex and birth weight of the baby were also noted. All the variables were entered in a database file and analysed by using Statistical program for social sciences (SPSS version 10).

Congenital abnormalities occurred among 2.8% of all deliveries. During the study period from January 2001-December 2003, a total of 8793 deliveries were reported. Out of these 170 cases of congenital abnormalities were identified and they served as the study population. These included terminations, live births and still births.

The mean age of the women in this study was 27.3 years with SD ± 5.3. Among the study subjects 11.6% were women above the age of 35 years. Only 8.8% of them had a previous history of congenital malformations. Consanguinity was found in 18.2% of cases. The mean gestational age at the time of ultrasound scan was 25.8 weeks (SD ± 6.8)

Ultrasound examination was performed by different operators. These ranged from those classed as level one to level 3. Forty percent of these ultrasounds were performed outside the hospital and for the purpose of analysis they have been put together in miscellaneous or others.

The ultrasound was able to diagnose congenital abnormalities in just under half of the cases (48.8%) whereas in 51.2% (83) malformations could not be diagnosed. The spectrum of abnormalities is shown in Table 2.

The most frequent abnormalities detected by ultrasound scan were of the kidney (19/20) followed by central nervous system (30/36). The details of abnormalities of the systems can be seen in Table 3.

The current study evaluates various aspects of ultrasound screening at a teaching hospital in Karachi. Congenital abnormalities complicated about 2-3% of all pregnancies. This is consistent with that reported in the literature,1-3 but higher than that reported by the EUROSCAN group.4 This can be attributed to the high risk women seen in our population.

The sensitivity of ultrasound in the detection of foetal anomalies is dependent on the prevalence of anomalies in a study population, the expertise of the examiner, the gestational age at scanning, the definition of anomaly-major and minor, and the postnatal ascertainment of anomalies.

The sensitivity of the ultrasound scan for diagnosing congenital abnormalities in this study was 48.8%. Other studies have reported the sensitivity of ultrasound scan to be from 22-41%8-10 to as high as 74-85%.5-7 This can be due to the way these studies were conducted. Levi et al found in the earlier part of their study a lower sensitivity but later this improved as the technique and training improved.9

Consangiunity is also considered to be a risk factor for congenital abnormalities.11 This association was not found in our study as consangiunity was found in only 18.2% of these cases.

The skill and experience of the sonographers is a critical factor in the detection of foetal anomalies.3 As the ultrasound scans in this study were performed by people of varying experience, this can explain why approximately half of these abnormalities were missed on the examination in our study group.

The ultrasound scan failed to detect any facial defects in our study. Low prediction rate of 17.5% has been reported by some of the earlier studies.12 However, more recent stduies claim the overall detection rate of as high as 65%.13-15

Similarly only a quarter of cardiac defects were diagnosed on the scan. The EURO scan study reported the sensitivity between 14-45%.9 Eurenius et. al10 has also reported similar results. The low detection rate was because the four chamber view was not included in the scan in their study population.

Based on our results we conclude that the antenatal ultrasound scan can be improved by incorporating four chamber views of the heart and careful look at the face during ultrasound examination. In addition, high risk women should be scanned in specialist units.

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2. Carrera JM, M Torrents, Mortera C, Cusi V, Munoz. A Routine prenatal ultrasound screening for fetal abnormalities: 22 years experience. Ultrasound Obstet Gynecol 1999;5:174-79.

3. Zimmer EZ, Avraham Z, Sujoy P, Goldstien I, Bronshtien M.. The influence of Prenatal ultrasound on the Prevalence of congenital anomalies at birth. Prenatal diagnosis 1997;17:7623-28.

4. Van Dorsten Peter J, Hulsey Thomas C, Newman Roger B, Menard Kathyrn. Fetal anomaly detection by second trimester ultrasonography in a tertiary center Am J Obstet Gynecol 1998;178:742-49.

5. Chitty LS, Hunt GH, Moore J, Lobb Mo. Effectivenes of routine ultraonography in detecting fetal structural abnormalities in a low risk population. BMJ 1991;303:1165-9.

6. Chitty LS. Ultrasound screening for fetal abnormalities. Prenatal Diagnosis 1995;15:1241-57.

7. Luck CA. The value of routine ultrasound scanning at 19 weeks: a four year study of 8849 deliveries. Br Med J 1992;304:1474-8.

8. Ewingman BC, Crane JP, Frigoletto FD, Leferve ML, Bain BP, McNellis D, et al. Effects of Prenatal ultrasound scanning on Perinatal outcome. N Eng J Medicine 1993;329:821-7.

9. Levi S, Schaaps P J, Dehavay De, Coulon R, Defoort P. End result of routine ultrasound screening for congenital anomalies: The Belgian Multicenter study 1984-92 Ultrasound Obstet Gynecol 1995;5:366-71.

10. Eurenius K, Axelsson O, Cnattingius S, Eriksson L, Norsted T. Second trimester ultrasound screening performed by midwives: sensitivity for detection of fetal anomalies Acta Obstet Gynecol Scandinavia 1999:78; 98-104.

11. Agarwal SS, Singh U, Singh PS, Das V, Sharma A, Mehra A, Chandravati, Malik GK, Misra PK. Prevalence and Spectrum of congenital malformations in a prospective study at a teaching Hospital. Indian Medical Res 1991;94:413-9.

12. Clementi M, Tenconi R, Bianchi F, Stoll C. Evaluation of prenatal diagnosis of cleft lip with or without cleft palate and cleft palate by ultrasound: experience from 20 European registries. EUROSCAN study group: Prenat Diagn 2000;20:870-5.

13. Cash C, Set P, Coleman N. The accuracy of antenatal ultrasound in the detection of facial cleftsin a low risk screening population.Ultrasound in Obstetrics and Gynecology 2001;18:432-36.

14. Jones MC. Prenatal diagnosis of cleft lip and palate: detection rates, accuracy of ultrasonography, associated anomalies, and strategies for counselling. (Review) Cleft Palate Craniofac J. 2002;39:169-73.

15. Stoll C, Tenconi R, Clementi M. Detection of congenital anomalies by Fetal Ultrasonographic examination across Europe. Community genetics 2001;4:225-32.