November 2004, Volume 54, Issue 11

Original Article

Effectiveness of Early Pregnancy Ultrasound in diagnosing Fetal abnormalities in High Risk Women

S.Munim  ( Department of Obstetrics and Gynaecology, The Aga Khan University Hospital, Karachi. )
N. Khowaja  ( Department of Obstetrics and Gynaecology, The Aga Khan University Hospital, Karachi. )

Abstract

Objective: To assess the efficacy of 11-14 weeks ultrasound in the diagnosis of fetal abnormalities in high risk women.

Methods: Prospective study conducted at a Teaching hospital in Karachi, Pakistan. One hundred ultrasound (mini-anomaly) scans were performed on 97 high-risk women, between 11-14 weeks of gestation.

Results: The most common indication for the ultrasound scan in the study, was previous history of structural or chromosomal abnormalities (40%) followed by advanced maternal age (22%). Out of 100 ultrasounds performed, two were found to have structural abnormalities at the time of mini-anomaly scan performed at 11-14 weeks. None of the ultrasound scans found to be normal at 11-14 weeks showed an abnormality on the subsequent scans.

Conclusion: Ultrasound scan performed between 11-14 weeks of pregnancy is effective in diagnosing major fetal abnormalities in the high-risk population. It can complement the anomaly scan performed in the second trimester, as some of the abnormalities become evident later in pregnancy (JPMA 54:542;2004).

Introduction

Second trimester ultrasound scan has become an essential part of antenatal care. In cases where a major structural defect is identified, termination of pregnancy is offered.1,2 The morbidity and mortality of this procedure increases with advancing gestation. Therefore early detection of such abnormalities will result in the reduction of such complications.

The benefits of early pregnancy ultrasound have been described by many workers.3-5 Timor Tritsch et al.3 suggested that transvaginal ultrasound done as early as 9-12 weeks, is helpful in the diagnosis of structural abnormalities. As the good quality equipment is becoming available it is possible to perform similar examination by transabdominal route. The role of first trimester ultrasound has been evaluated for the low risk population. 6,7

We embarked on this study to evaluate the role 11-14 weeks ultrasound in the detection of fetal abnormalities in the high-risk population. This study is part of a bigger project on first trimester screening.

Material and Methods

This is a prospective study conducted in the department of Obstetrics and Gynaecology, at the Aga Khan University Hospital, Karachi, Pakistan. Karachi is the largest city of Pakistan, with an estimated population of 10-12 million belonging to different ethnicity and socio-economic background.

The Aga Khan University Hospital is a tertiary care teaching hospital in the private sector equipped with the latest diagnostic and therapeutic facilities and a well equipped neonatal intensive care unit. About 3000 deliveries take place every year. The services of Prenatal diagnosis has only become available in the last two years. In the department of Obstetrics and Gynaecology two antenatal ultrasounds in pregnancy are performed, one at 11-14 weeks and the other between 18-22 weeks. A third trimester ultrasound is requested when indicated.

We performed about 100 ultrasounds on 97 high risk pregnant women in early pregnancy between January 2001- September 2002. The study subjects were seen in the antenatal clinics, counselled and referred for ultrasound by their respective consultants. A single operator performed all the ultrasounds after obtaining a verbal consent, on a Toshiba Nemio machine, using 3.75 MHz probe. Most of the ultrasounds were performed by transabdominal route. A transvaginal scan was performed in cases where the quality of ultrasound was unacceptable.

For maintaining the quality of the scan, the outcome of each pregnancy was monitored. The variables noted were weight of the baby, apgar scores and any additional abnormality at the time of birth.

All the above-mentioned variables along with the ultrasound details and demographic variables including gestational age were entered in a database file and analysed by SPSS version 10.

Results

In a two-year period 100 ultrasound scans were performed on 97 high risk pregnant women at a mean gestation of 12.4 days. There was one set of twins and of triplets each in this study. The mean maternal age was 30.98 years (range 18-42 years). The study subjects were referred because of their risk factors (Table 1).
Table 1. Details of anatomical survey at the time of scan.
Head and brain
Heart, four chamber view and its position
Stomach bubble and its position
Umbilical cord insertion and anterior abdominal wall
Extremities including the position of hands and feet and number of digits
spine
bladder and kidneys
The indications of the scans are autined in Table2.

Table 2. Indications of the scans.
Indication No.
Advanced maternal age 22
Previous history of Down's syndrome 7
Family history of chromosomal abnomalities 3
Previous history of congential abnormality 29
Previous pregnancy complicated by miscarriage  
Intrauterine death or neonatal death 18
Previous child with cerebral Palsy 4
History of bleeding in the current pregnancy 2
Multiple Pregnancy 5
Anmpr,a;otu detected on scan in the present pregnancy 1
Pregnancy complication like Diabetes 2
Previous history of Thalasemia/ Cystic fibrosis 5
Discrepancy in dates 2
Total 100

Three of the cases were found to have a non-viable pregnancy at the time of the scan. There were two cases of fetal abnormalities and the rest of the ultrasounds were normal. In one case the fetus had megacystis which increased in size. In the other case the fetus had encephalocoele, khyphoscoliosis and early onset fetal growth restriction. Following counselling both couples opted for termination of pregnancy but declined autopsy. The abnormalities were confirmed postnatally in the patient with encephalocoele and khyphosis. A huge abdominal mass was seen after termination in the one with Megacystis. No additional abnormality was seen on the subsequent scans.

Seven percent of the women were lost to follow up. The remaining 93% pregnancies were followed till delivery. No additional abnormality was seen in any of the cases postnatally.

Discussion

Our study demonstrates that 11-14 weeks ultrasound is effective in diagnosing fetal abnormalities in the high-risk population. Both fetal abnormalities were detected by the early scan and no additional abnormality was found on subsequent ultrasound scans. Den Hollander and co-workers8 have also found the 11-14 weeks ultrasound to be 91% effective. While others have reported this to be between 57-89%. 7,9,10

The incidence of missed abortions was found to be 3% in the study sample. This is consistent with the findings of the other studies.10 The advantage of early diagnosis of missed abortion helps in planning for the elective treatment and hence reduces the chances of bleeding and emergency evacuation of retained products of conception.

A single operator performed all the ultrasounds after receiving extensive training. This is because the sensitivity for detection of fetal abnormalities increases after a learning curve of 3-4 years.11 Operators with varying experience would have affected the of this study.

Cranial defects, being early onset fetal abnormalities, can be diagnosed in the first trimester. In this study encephalocoele was detected as early as 12 weeks. Ossification of skull is not complete before 11 weeks of gestation, therefore this diagnosis is made beyond this period. Encephalocoele can be isolated or be a part of Meckel Gruber Syndrome. The diagnosis of this syndrome is therefore possible at the first trimester scan. It is difficult in the second trimester due to oligohydramnios. 12

Fetal bladder is also seen successfully at this stage. Half of the cases of megacystis found at 10-14 weeks of gestation, resolves spontaneously. The rest of the cases are due to chromosomal abnormality or obstructive uropathy.13 The decision of termination of pregnancy was made on the basis of increasing size of the bladder and severe oligohydramnios. As the autopsy was not performed in this case, the exact diagnosis could not be established.

In conclusion, early ultrasound is effective in diagnosing fetal abnormalities in the high risk population. It not only provides reassurance in case of a normal ultrasound but also enables a decision on early termination if there is an abnormality. Autopsy remains the most important investigation to confirm prenatal diagnosis and aids in future counselling. This study has the limitation that autopsies could not be performed to confirm the diagnosis after the termination of pregnancy. We recommend that early ultrasound should be used to complement the 18-23 weeks scans as the natural history of certain abnormalities does not allow early diagnosis.

References

1. Royal College of Obstetricians and Gynecologists Report of the working party on ultrasound screening for Fetal abnormalities, 1997.

2. Lee K, Kim SY, Choi SM, et al. Effectiveness of prenatal ultrasonography in detecting fetal anomalies and perinatal outcome of anomalous fetuses. Yonsei Med J. 1998; 39:372-382.

3. Timor Tritsch I, Farine D, Rosen MG. A close look at early embryonic development with high frequency transvaginal transducer. Am J Obstet Gynecol 1988;159:676-81.

4. Souka AP, Nicolaides KH. Diagnosis of fetal abnormalities at 10-14 weeks scan. Ultrasound in Obstet Gynecol 1997;10:429-42.

5. Nicolaides KH, Heath V, Liao AW. The 11-14 week scan. Baillieres Best Pract Res Clin Obstet Gynaecol 2000;14:581-94.

6. Economides DL, Braithwaite J. First trimester ultrasonographic diagnosis of fetal structural abnormalities in a low risk population. Br J Obstet Gynaecol 1998;105:53-7.

7. Economides DL, Braithwaite JM. A review ultrasonography in the detection of fetal anomalies in early pregnancy. Br J Obstet Gynaecol 1999;106:516-23.

8. Den Hollander NS, Wessels M W, Neirmeijer MF, et al. Early fetal anomaly scanning in a population at increases risk of abnormalities. Ultrasound Obstet Gynecol 2002;19:570-4.

9. Achiron R, Tadmor O. Screening for fetal anomalies during the first trimester of pregnancy: Transvaginal versus transabdominal sonography. Ultrasound Obstet Gynecol 1991;1:186-91.

10. Drysdale K, Ridley D, Walker K, et al. First trimester scanning as a screening tool for high-risk and abnormal pregnancies in a district general hospital setting. J Obstet Gynaecol 2002;22:159-65.

11. Taipale P, Ammala M, Salonen R , et al. Learning curve in ultrasonographic screening for selected structural anomalies in early pregnancy. Obstet Gynecol Volume 2003;101;273-8.

12. Tanriver HA, Hendrick HJ, Ertan K, et al. Meckel Gruber Syndrome: a first trimester diagnosis of a recurrent case. Eur J Ultrasound 2002;15:69-72.

13. Sebire NJ, Von C, Kaisenberg R, Rubio C. Fetal megacystis at 10-14 weks of gestation. Ultrasound Obstet Gynecol 1996;8:387-90.

Journal of the Pakistan Medical Association has agreed to receive and publish manuscripts in accordance with the principles of the following committees: