Antenatal macrosomia prediction using sonographic fetal abdominal circumference in South Tunisia

Antenatal macrosomia prediction using sonographic fetal abdominal circumference in South Tunisia

 

Kais Chaabane¹, Khaled Trigui^1,&, Doulira Louati¹, Sahbi Kebaili¹, Hichem Gassara¹, Abdallah Dammak¹, Habib Amouri¹, Mohamed Guermazi¹

 

¹Obstetrics and Gynecology Department, Hédi Chaker Academic Hospital- Sfax-Tunisia

 

 

^&Corresponding author
Khaled Trigui, Obstetrics and Gynecology Department, Hédi Chaker Academic Hospital, 3029 Sfax - Tunisia

 

 

 

 

Fetal macrosomia defined as infant birth weight ≥ 4000g, is associated with many adverse outcomes, which can be the cause of high rate perinatal maternal and fetal morbidity and mortality. Accurate methods for prenatal prediction of macrosomia would therefore be very useful for planning labor and delivery strategies and consequently prevent from its complications. Ultrasonographic assessment of fetal growth to estimate fetal weight is widely used in obstetrics. Several criteria and models to calculate them are proposed. The purpose of this study was to evaluate the diagnostic value of ultrasonographic measurement of fetal abdominal circumference over 350 mm for the prediction of fetal macrosomia ,to determine factors associated with the failure to detect this thereshold in some macrosomic infants ,and to assess its value in predicting shoulder dystocia.

 

 

A retrospective controlled case study was conducted between january 2007 and december 2008 in the Department of Obstetrics and Gynecology of Sfax Tunsia.During this period, we registerd a total of 18289 deliveries,including 1283 macrosomic infants (7%).

Stastical comparaison was performed between a group of women delivering liveborn neonates between 37 and 42 weeks weighing more than 4000g and a group of women with the same inclusion criteria except infant weight which was less than 4000 g. For all women the sonographic examination must have been performed within 72 hours before delivery, in order to eliminate the possible effect of the time elapsed between ultrasound abdominal circumference examination and delivery for actual fetal weight.Finally the two groups included 465 women each.

A regression analysis was used to evaluate the best linear relationship between abdominal circumferance (AC), biparietal diameter (BPD), femur length (FL) and birth weight (BW). Odds ratios for each criteria, were calculated, and significance was tested with the Chi 2 test.

To evaluate factors associated with the failure of detection of an AC ≥ 350 mm in macrosomic neonates, we compared maternal characteristics in two groups of this population : the group 1 includes macrosomics with an AC over 350mm and group 2 enclosing macrosomics with an AC less than 350mm. Statistical comparison was made by « chi 2 » for the frequencies and « Student » test for the means. Logistic regression analysis was used to determine significant predictors of shoulder dystocia.

 

 

The median of AC was 367.7mmm in the macrosomic group, and 330.4 mm in the non macrosomic. The difference was significant (P<0.001).Birth weight was significantly highter in macrosomic (4152g versus 3360g P<0.001) (Table 1). Chi square regression analysis using birth weight as dependant variable and AC, BPD and FL as independant variable showed that AC alone was the best factor predicting birth weight in macrosomic neonates (r=0.8, P<0.001).compared with the BPD (r=0.67, P<0.001) and FL (r=0.7, P<0.001).

A cut-off value AC over 350mm,was found significantly more frequent in macrosomic (78.7% n=366) compared with the non macrosomic (23.5% n=109) (Table 1).The accuracy and predictibiliy of 350 mm AC for detecting macrosomia were sensitivity (78.7%), specificity (76.8%), negative predictive value (49.2%), and positive predictive value (92.6%), (Table 2).

In the macrosomic group we noticed that 21.3% (n=99) of this population had AC less than 350 mmm. Analysing factors that could be interfering with the detection of this threshold im macrosomic fetuses, we found that a history of macrosomia was more frequent in group 1 than in group 2 (7.6% versus 4%, p<0.001).Body mass index (BMI) over 30 was more frequent in group 2 (31.3% versus 17.4%,P<0.001).There was no significant difference in maternal age (P=0.2),gestational age (P=0.2), neither in BMI between 25 and 29 (P=0.12).Actual birth weight was statististically no different between both groups (4187g in group 1, 4123g in group 2 ,p=0.18) (Table 3).

In macrosomic neonates, shoulder dystocia occured in 67 cases when AC ≥ 350mm (18.3%) and in 10 cases when AC<350mm (10.1%), P<0.01. In non macrosomic infants, shoulder dystocia was found in 3 cases when AC≥350mm (2.8%) and in 3 cases when AC< 350mm (0.8%), P<0.01 (Table 4).

Logistic regression ,with shouder dystocia as independant variable and AC≥350mm as dependant variable showed than AC over a cut off value of 350mm alone was associated with shoulder dystocia (OR=2.85, 95 %confidence interval 1.4, 7.4, P<0.01).

 

 

Macrosomia is a cause of the worst of obstetric emergencies such as shoulder dystocia, birth asphyxia, and postpartum hemorrhage. [1, 2] About half of shoulder dystocia happen to macrosomic infants, yet frequency of macrosomia is less than 10%. Shoulder dystocia cannot always be predicted accurately. However, predicting macrosomia can help to identify the population at the highest risk for shoulder dystocia. Several studies of sonographic measurement for predicting of fetal macrosomia were established [3-5].

Campbell and Wilkin [6] first emphasized the importance of ultrasound AC measurements in determining fetal size in 1975. Smith et al compared the accuracy of two sonographic fetal weight-estimation models and AC as a single measure for the prediction of fetal macrosomia and found that models based on three biometric indices including AC, BPD, and FL appeared to be less accurate for the diagnosis of fetal macrosomia than models based on AC as a single measure [7].

Several studies have shown that an AC measurement ≥ 350 mm was the best predicting value of fetal macrosomia [8,9].This conclusion was matching with our results with an accuracy of 77%.

Comparing our results with previous studies, we found that the negative predictive value was lower (49.2%).So we analysed factors that could be associated with the failure of detection an AC ≥ 350mm in macrosomic infants, we found that obesity was significantly higher when AC<350mm.This may be explained by the fact that ultrasound performance could be minimized by maternal adiposity [10].

Shoulder dystocia remains a serious obstetric emergency and although not always predictable, it is clear that large fetuses are at greatest risk for it. Sonographic detection of this complication was a subject of high interest for clinicians. Jazayeri and al found that all infants presenting shoulder dystocia had an AC more than 350mm, reagardless the actual birth weight [11].Inour study we found similar results.

We emphasize that the population used in this study was larger than previous studies [4, 5, 11]. Most of other researches included about one hundred samples. In this study, we included 465 samples hoping to decrease the bias of sample distribution.

The accuracy of our retrospective study in this population of pregnant women needs to be tested in other populations to confirm its applicability. Because not all patients at risk for shoulder dystocia can be identified, all persons delivering infants must be trained in its appropriate management.

 

 

Abdominal circumference measurements were useful in screening for suspected macrosomia, An AC measurement of 350 mm or more could help to suspect shoulder dystocia, and therefore motivate obsteticians to be more vigilant during the delivery.

 

 

The authors declare that they have no competing interests.

 

 

Conception and design: Kais Chaabane, Khaled Trigui. Administrative support: Kais Chaabane. Collection and assembly of data: Khaled Trigui, Doulira Louati. Data analysis and interpretation: Sahbi Kebaili, Hichem Gassara. Manuscript writing: Kais Chaabane, Khaled Trigui, Abdallah Dammak. All the authors have read and approved the final version of the manuscript.

 

 

The authors are grateful to the medical, nursing and scientific staffs of the Obstetrics and Gynecology Department of Hédi Chaker Academic Hospital who were involved in the care of the patients studied.

 

 

Table 1: The Abdominal circumference > 350 mm in predicting fetal macrosomia

Table 2: The diagnostic value of AC > 350 mm in predicting fetal macrosomia

Table 3: Maternal characteristics in macrosomic group

Table 4: Incidence of shoulder dystocia according to the threshold of 350 mm

 

 

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