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Accuracy of prediction of gestational age by ultrasound measurement of biparietal diameter in Nigerian women
217
Int. J. Gynecol. Obstet., 1989.28: 217-219 International Federation of Gynecology and Obstetrics
Accuracy of prediction of gestational age by ultrasound measurement of biparietal diameter in Nigerian women F.E. Okonofua
and F.A. Atoyebi
Department of Obstetrics, GynaecologV and Perinatology, Obqfemi A wolowo University, Ile-Ife (Nigeria) (Received January 22nd. 1988) (Accepted March 7th, 1988)
Abstract The accuracy of assessment of gestational age by ultrasound measurement of biparietal diameter (BPD) was evaluated in 84 Nigerian women. Ultrasound and menstrual delivery dates were compared in these women who had no complications of pregnancy and delivered infants whose birthweights were appropriate for 40 weeks. The results showed that ultrasound dating was more accurate than menstrual dating as evident from the number of women who delivered on and within 1 or 2 weeks of predicted delivery dates. It is concluded that (I) our locally produced BPD normogram is as accurate as those from elsewhere and (2) the normogram is recommended for use in Nigerian women for accurate pregnancy dating. Keywords: Biparietal diameter; Menstrual dates; Ultrasound dates; Biparietal diameter; Normogram . Introduction Several workers [4,7] have shown that ultrasound measurement of the fetal biparietaI diameter (BPD) in early pregnancy gives an accurate estimate of gestational age. Specifically, a single BPD measurement between 0020-7292/89/$03.50
0 1989 International Federation of Gynecology and Obstetrics Published and Printed in Ireland
16 and 20 weeks of pregnancy is known to give an accurate estimation of gestational age to within 1 week [2]. In Nigeria, our recent studies [l] and those of others [5] showed that a slower rate of BPD growth occurs in Nigerian women. Consequently, in the past years, we have used our locally produced BPD growth chart for assigning gestational age in this population. In this study, the accuracy of gestational age assessment using our locally produced normogram was investigated and comparison made with predictions based on menstrual dates. Materials and methods The study consisted of all women who had ultrasound cephalometry performed at the Obafemi Awolowo University Teaching Hospital, Nigeria because of uncertain maturity. The gestational age was considered to be uncertain when the date of the last menstrual period was inconsistent, when bleeding occurred in early pregnancy and when there was a clinical discrepancy between actual and expected uterine size in excess of 2 weeks. Clinical details were deliberately made unavailable to the ultrasonographer and delivery date was predicted from the measurement of fetal BPD as a blind trial. All BPD measureClinical and Clinical Research
218
OkonofuaandAtoyebi
ments were done before 30 weeks of pregnancy and all patients had some knowledge of their menstrual dates. The method of ultrasonic measurement of fetal BPD was as previously described [I]. The ultrasound machine used was a 2130 ADR linear array real-time ultrasound with a 3.8 MHz transducer. Our previous study had shown a linear growth of fetal BPD in Nigerian women. All BPD measurements obtained in this study were fitted into that normogram and the gestational ages were estimated by extrapolation from the mean value. In each case, a day of delivery was subsequently determined by counting forward from the day of measurement. All the patients were followed up to term. The expected delivery date calculated from the ultrasonic measurement (ultrasonic EDD) was then compared with that calculated from the patient’s last menstrual period (Menstrual EDD) in relation to the final outcome. Only women who went into spontaneous labor and delivered infants whose birthweights were above the tenth centile for 40 weeks for the population [6] were included in the final analysis. Statistical analysis was performed by determining the number of women who delivered within 1 or 2 weeks of menstrual and ultrasound predicted delivery dates. The two groups were then compared using x2 statistical method. Results Of the 110 patients in whom there was some doubt about the duration of pregnancy, 94 went into spontaneous labor; labor was induced in the remaining 16. Ten patients were excluded from analysis because the infants’ birthweights fell below the 10th centile for 40 weeks; therefore, only 84 women were studied. Twelve of the 84 patients (14.3%) delivered on the days predicted by ultrasound whereas only 3 patients (3.6%) delivered on days estiInt J Gynecol Obstet 28
mated from known days of last menstrual period. This difference achieved statistical significance (x2 test = 4.68, P < 0.05). Similarly, 69/84 (82. lolo) ultrasound predictions were correct to within 1 week of predicted dates. When this is compared to predictions based on LNMP, where only 42184 (50.0%) delivered within 1 week, it is clear that ultrasound prediction is superior (x” test = 15.4, P< 0.001). Since term delivery can still occur within 2 weeks of predicted dates, we determined the proportion of women who delivered within this time period. Our results showed that 96.4% of the women delivered within 2 weeks when prediction is made with ultrasound. With prediction based on LNMP, the corresponding figure was 67.9%. This difference was also highly statistically significant (x2 test = 21.5,P< 0.001). Induction of labor was performed in 16 patients. The indications were prolonged pregnancy in 8, premature rupture of membrane in 4, pre-eclampsia in 2 and antepartum hemorrhage in 2. Pregnancy was considered prolonged when the duration of pregnancy was 14 days beyond 40 weeks as estimated by ultrasound cephalometry. The clinical examination of these infants by pediatricians confirmed the maturity assessed by ultrasound cephalometry. Discussion The study was designed to determine the accuracy of our locally produced BPD normogram in the assessment of gestational age. Our results indicate that ultrasonic measurement of fetal BPD is superior to known menstrual dates in the assessment of fetal gestational age. Previous work in several caucaSian populations showed a similar better accuracy for ultrasound cephalometry in fetal gestational age assessment. According to Campbell [3], 84% of women who had second trimester ultrasound cephalometry for dating went into spontaneous labor within 9 days of predicted delivery dates although,
BPD in gestational age prediction
95% was expected. However, in the series reported by Varma [8], 91.2% delivered within 9 days which was slightly better than that reported by Campbell. These data compare favorably with our present finding that 82% of our women delivered within 1 week of ultrasound predicted delivery dates. This confirms the superiority of ultrasound over menstrual dates in gestational age assessment. Several reports indicate that with ultrasound cephalometry, 95% of true dates do not deviate from the predicted age by more than 9-l 1 days [4,7,8]. In our series, 96% of the patients delivered within 2 weeks. This range implies that in evaluating a particular pregnancy with ultrasound dating, it would be extremely improbable to be significantly erroneous. Since our assessment results tally with results obtained with early normograms. it indicates that our BPD normogram is accurate for use in this population. Unfortunately, the BPD normogram cannot be used after 30 weeks gestation becaue of flattening that occurs in BPD growth chart after this period. We recently found that normogram of ultrasonic fetal abdominal circumference has lesser tendency to late pregnancy flattening [9]. Therefore, it would be of clinical interest to determine the usefulness of this parameter in assessing gestational age in late pregnancy.
219
References Ayangade SO, Okonofua FE: Normal growth of the fetal biparietal diameter in an African Population. Int J Gynaecol Obstet 24: 35.1986. Bennett MJ, Little G. Dewhurst J, Chamberlain G: Predictive value of ultrasound measurement in early pregnancy: a random&d controlled trial. Br J Obstet Gynaecol89: 338.1982. Campbell S: The prediction of fetal maturity by ultrasonic measurement of the biparietal diameter. J Obstet Gynaecol Br Commonw 76: 603.1969. Campbell S: The assessment of fetal development by ultrasound. J Clin Perlnatol I: 507,1974. Okupe RF. Coka 00, Gbajumo SA: Assessment of fetal biparietal diameter during normal pregnancy in Nigerian women. Br J Obstet Gynaecol91: 629,1984. Olowe SA: Standards of intrauterine growth for an African population at sea level. Trop Paediatr 99: 489,1978. Sabbagha R. Turner H, Rockette H, Mazer J, Orgill J: Sonar BPD and fetal age: definition of the relationship. Obstet Gynaecol43: 7,1974. Varma TR: Prediction of delivery date by ultrasound cephalometry. J Obstet Gynaecol Br Commonw 80: 316, 1973. Okonofua FE. Ayangade SO, Ajibulu AO: Ultrasound measurement of fetal abdominal circumference and the ratio of biparietal diameter to transverse abdominal diameter in a mixed Nigerian population. Int J Gynaecol Obstet27: 1, 1988. Address for reprints: F.E. Okonofna Department of Obntetries and Gynaecology Faculty of Haitb !Sdences Obafemi Awolowo University Ile-Ife, Nigeria
Clinical and Clinical Research
Int. J. Gynecol. Obstet., 1989.28: 217-219 International Federation of Gynecology and Obstetrics
Accuracy of prediction of gestational age by ultrasound measurement of biparietal diameter in Nigerian women F.E. Okonofua
and F.A. Atoyebi
Department of Obstetrics, GynaecologV and Perinatology, Obqfemi A wolowo University, Ile-Ife (Nigeria) (Received January 22nd. 1988) (Accepted March 7th, 1988)
Abstract The accuracy of assessment of gestational age by ultrasound measurement of biparietal diameter (BPD) was evaluated in 84 Nigerian women. Ultrasound and menstrual delivery dates were compared in these women who had no complications of pregnancy and delivered infants whose birthweights were appropriate for 40 weeks. The results showed that ultrasound dating was more accurate than menstrual dating as evident from the number of women who delivered on and within 1 or 2 weeks of predicted delivery dates. It is concluded that (I) our locally produced BPD normogram is as accurate as those from elsewhere and (2) the normogram is recommended for use in Nigerian women for accurate pregnancy dating. Keywords: Biparietal diameter; Menstrual dates; Ultrasound dates; Biparietal diameter; Normogram . Introduction Several workers [4,7] have shown that ultrasound measurement of the fetal biparietaI diameter (BPD) in early pregnancy gives an accurate estimate of gestational age. Specifically, a single BPD measurement between 0020-7292/89/$03.50
0 1989 International Federation of Gynecology and Obstetrics Published and Printed in Ireland
16 and 20 weeks of pregnancy is known to give an accurate estimation of gestational age to within 1 week [2]. In Nigeria, our recent studies [l] and those of others [5] showed that a slower rate of BPD growth occurs in Nigerian women. Consequently, in the past years, we have used our locally produced BPD growth chart for assigning gestational age in this population. In this study, the accuracy of gestational age assessment using our locally produced normogram was investigated and comparison made with predictions based on menstrual dates. Materials and methods The study consisted of all women who had ultrasound cephalometry performed at the Obafemi Awolowo University Teaching Hospital, Nigeria because of uncertain maturity. The gestational age was considered to be uncertain when the date of the last menstrual period was inconsistent, when bleeding occurred in early pregnancy and when there was a clinical discrepancy between actual and expected uterine size in excess of 2 weeks. Clinical details were deliberately made unavailable to the ultrasonographer and delivery date was predicted from the measurement of fetal BPD as a blind trial. All BPD measureClinical and Clinical Research
218
OkonofuaandAtoyebi
ments were done before 30 weeks of pregnancy and all patients had some knowledge of their menstrual dates. The method of ultrasonic measurement of fetal BPD was as previously described [I]. The ultrasound machine used was a 2130 ADR linear array real-time ultrasound with a 3.8 MHz transducer. Our previous study had shown a linear growth of fetal BPD in Nigerian women. All BPD measurements obtained in this study were fitted into that normogram and the gestational ages were estimated by extrapolation from the mean value. In each case, a day of delivery was subsequently determined by counting forward from the day of measurement. All the patients were followed up to term. The expected delivery date calculated from the ultrasonic measurement (ultrasonic EDD) was then compared with that calculated from the patient’s last menstrual period (Menstrual EDD) in relation to the final outcome. Only women who went into spontaneous labor and delivered infants whose birthweights were above the tenth centile for 40 weeks for the population [6] were included in the final analysis. Statistical analysis was performed by determining the number of women who delivered within 1 or 2 weeks of menstrual and ultrasound predicted delivery dates. The two groups were then compared using x2 statistical method. Results Of the 110 patients in whom there was some doubt about the duration of pregnancy, 94 went into spontaneous labor; labor was induced in the remaining 16. Ten patients were excluded from analysis because the infants’ birthweights fell below the 10th centile for 40 weeks; therefore, only 84 women were studied. Twelve of the 84 patients (14.3%) delivered on the days predicted by ultrasound whereas only 3 patients (3.6%) delivered on days estiInt J Gynecol Obstet 28
mated from known days of last menstrual period. This difference achieved statistical significance (x2 test = 4.68, P < 0.05). Similarly, 69/84 (82. lolo) ultrasound predictions were correct to within 1 week of predicted dates. When this is compared to predictions based on LNMP, where only 42184 (50.0%) delivered within 1 week, it is clear that ultrasound prediction is superior (x” test = 15.4, P< 0.001). Since term delivery can still occur within 2 weeks of predicted dates, we determined the proportion of women who delivered within this time period. Our results showed that 96.4% of the women delivered within 2 weeks when prediction is made with ultrasound. With prediction based on LNMP, the corresponding figure was 67.9%. This difference was also highly statistically significant (x2 test = 21.5,P< 0.001). Induction of labor was performed in 16 patients. The indications were prolonged pregnancy in 8, premature rupture of membrane in 4, pre-eclampsia in 2 and antepartum hemorrhage in 2. Pregnancy was considered prolonged when the duration of pregnancy was 14 days beyond 40 weeks as estimated by ultrasound cephalometry. The clinical examination of these infants by pediatricians confirmed the maturity assessed by ultrasound cephalometry. Discussion The study was designed to determine the accuracy of our locally produced BPD normogram in the assessment of gestational age. Our results indicate that ultrasonic measurement of fetal BPD is superior to known menstrual dates in the assessment of fetal gestational age. Previous work in several caucaSian populations showed a similar better accuracy for ultrasound cephalometry in fetal gestational age assessment. According to Campbell [3], 84% of women who had second trimester ultrasound cephalometry for dating went into spontaneous labor within 9 days of predicted delivery dates although,
BPD in gestational age prediction
95% was expected. However, in the series reported by Varma [8], 91.2% delivered within 9 days which was slightly better than that reported by Campbell. These data compare favorably with our present finding that 82% of our women delivered within 1 week of ultrasound predicted delivery dates. This confirms the superiority of ultrasound over menstrual dates in gestational age assessment. Several reports indicate that with ultrasound cephalometry, 95% of true dates do not deviate from the predicted age by more than 9-l 1 days [4,7,8]. In our series, 96% of the patients delivered within 2 weeks. This range implies that in evaluating a particular pregnancy with ultrasound dating, it would be extremely improbable to be significantly erroneous. Since our assessment results tally with results obtained with early normograms. it indicates that our BPD normogram is accurate for use in this population. Unfortunately, the BPD normogram cannot be used after 30 weeks gestation becaue of flattening that occurs in BPD growth chart after this period. We recently found that normogram of ultrasonic fetal abdominal circumference has lesser tendency to late pregnancy flattening [9]. Therefore, it would be of clinical interest to determine the usefulness of this parameter in assessing gestational age in late pregnancy.
219
References Ayangade SO, Okonofua FE: Normal growth of the fetal biparietal diameter in an African Population. Int J Gynaecol Obstet 24: 35.1986. Bennett MJ, Little G. Dewhurst J, Chamberlain G: Predictive value of ultrasound measurement in early pregnancy: a random&d controlled trial. Br J Obstet Gynaecol89: 338.1982. Campbell S: The prediction of fetal maturity by ultrasonic measurement of the biparietal diameter. J Obstet Gynaecol Br Commonw 76: 603.1969. Campbell S: The assessment of fetal development by ultrasound. J Clin Perlnatol I: 507,1974. Okupe RF. Coka 00, Gbajumo SA: Assessment of fetal biparietal diameter during normal pregnancy in Nigerian women. Br J Obstet Gynaecol91: 629,1984. Olowe SA: Standards of intrauterine growth for an African population at sea level. Trop Paediatr 99: 489,1978. Sabbagha R. Turner H, Rockette H, Mazer J, Orgill J: Sonar BPD and fetal age: definition of the relationship. Obstet Gynaecol43: 7,1974. Varma TR: Prediction of delivery date by ultrasound cephalometry. J Obstet Gynaecol Br Commonw 80: 316, 1973. Okonofua FE. Ayangade SO, Ajibulu AO: Ultrasound measurement of fetal abdominal circumference and the ratio of biparietal diameter to transverse abdominal diameter in a mixed Nigerian population. Int J Gynaecol Obstet27: 1, 1988. Address for reprints: F.E. Okonofna Department of Obntetries and Gynaecology Faculty of Haitb !Sdences Obafemi Awolowo University Ile-Ife, Nigeria
Clinical and Clinical Research