Sub-Saharan African Journal of Medicine

ORIGINAL ARTICLE
Year
: 2015  |  Volume : 2  |  Issue : 1  |  Page : 14--18

Accuracy of ultrasound in fetal birth weight estimation and sex determination in singleton term pregnancies from two tertiary institutions of northwestern Nigeria


Sadisu Mohammed Ma`aji1, Daniel Dirioha Odunko2,  
1 Department of Radiology, Usmanu Danfodiyo University Teaching Hospital, Sokoto, Sokoto State, Nigeria
2 Department of Radiology, Federal Medical Center, Birnin Kebbi, Kebbi State, Nigeria

Correspondence Address:
Sadisu Mohammed Ma`aji
Department of Radiology, Usmanu Danfodiyo University Teaching Hospital, PMB 2370, Sokoto, Sokoto State
Nigeria

Abstract

Background: Ultrasonographic assessment of fetal growth for the estimation of fetal weight (EFW) is a common obstetrics practice and provides valuable information for planning the mode of delivery. The aim of this study is to determine the accuracy of fetal birth weight estimation and sex determination using ultrasonography from two tertiary institutions of Northwestern Nigeria. Materials and Methods: This was a prospective study involving 109 singleton uncomplicated pregnancies from January 2013 to January 2014. All the patients are booked at the antenatal clinic of two tertiary institutions (Usmanu Danfodiyo University Teaching Hospital [UDUTH] Sokoto and Federal Medical Center Birnin Kebbi). Inclusion criteria in the study were term pregnancy (36-42 weeks), reliable date of last menstrual period, regular menstrual cycle, a close correlation between menstrual age and clinical gestational age measurements. Results: The mean maternal age was 29.01 ΁ standard deviation 4.81 (range: 18-40 years). One hundred and nine term live-born singleton infants delivered at UDUTH and Federal Medical Center Birnin Kebbi during the study period had undergone ultrasound EFW <7 days preceding birth. Twenty-one (19.3%) fetuses were identified as male while 38 (34.9%) was identified as female during the ultrasound examinations. In about 40 (36.7%) of the fetuses, the gender was not seen. Conclusion: There was a significant error while estimating fetal weight by ultrasound and underestimation has the highest percentage. Determination of fetal sex with ultrasound show some degree of accuracy in our study because 21 (19.3%) fetuses were identified as male, while 38 (34.9%) was identified as female during the ultrasound examinations. Hence, it should be recommended only if the mother requested for the gender during the scanning taking into account the social implications.



How to cite this article:
Ma`aji SM, Odunko DD. Accuracy of ultrasound in fetal birth weight estimation and sex determination in singleton term pregnancies from two tertiary institutions of northwestern Nigeria.Sub-Saharan Afr J Med 2015;2:14-18


How to cite this URL:
Ma`aji SM, Odunko DD. Accuracy of ultrasound in fetal birth weight estimation and sex determination in singleton term pregnancies from two tertiary institutions of northwestern Nigeria. Sub-Saharan Afr J Med [serial online] 2015 [cited 2021 Jul 31 ];2:14-18
Available from: https://www.ssajm.org/text.asp?2015/2/1/14/151568


Full Text

 INTRODUCTION



Ultrasonographic assessment of fetal growth for the estimation of fetal weight (EFW) is a common obstetrics practice and provides valuable information for planning the mode of delivery. Most formulae were proposed in the early 1980s using different combinations of standardized fetal biometric parameters, such as the biparietal diameter (BPD), head circumference, abdominal circumference (AC) and femur length (FL). [1] The formulae have increased the accuracy of the fetal weight estimation significantly. [2],[3] Multiple formulae have been developed for the estimation for birth weight using ultrasound measurement. [4],[5],[6],[7],[8],[9],[10] The introduction of obstetric ultrasonography (US) has made it possible to visualize the fetus genitalia. Fetal sex determination is needed for the diagnosis of some important clinical conditions for example sex differentiation disorders, to rule out X-linked diseases in couples with a risk of transmitting the disease or when there is a risk for 21 hydroxylase deficiency which can lead to masculinization of female fetuses. Many parents are anxious to know the gender of fetuses accurately. The most commonly asked question next to fetal wellbeing is the gender of the fetus while doing obstetric ultrasound. [11]

The aim of this study is to determine the accuracy of fetal birth weight estimation and sex determination using US in two tertiary institutions of Northwestern Nigeria.

 MATERIALS AND METHODS



This was a prospective study involving 109 singleton uncomplicated pregnancies from January 2013 to January 2014. All the patients were booked at the antenatal clinic of two tertiary institutions (Usmanu Danfodiyo University Teaching Hospital [UDUTH] Sokoto and Federal Medical Center Birnin Kebbi). Inclusion criteria in the study were term pregnancy (36-42 weeks), reliable date of last menstrual period, regular menstrual cycle, a close correlation between menstrual age and clinical gestational age measurements. Patients with malpresentation, maternal diseases such as gestational diabetes, pulmonary tuberculosis, multiple pregnancies, and antenatal diagnosis of congenital fetal malformation or advanced labor were excluded. All examinations were performed using a Mindray DP 8800 plus and dynamic imaging concept D real-time ultrasound machines with a 3.5 MHz curvilinear transducer. Measurements were made with calibrated caliper on the machine on frozen images of BPD, AC, and the FL. Fetal gender was identified with the presence of sonographic features of external genitalia in the perineal region. The female was recognized by the presence of two oblong echogenic structures called labia folds separated by an echo-free area. The male was recognized by the presence of the scrotal sac as a rounded echogenic structure separated by an echogenic median raphe and the phallus as an echogenic cylindrical structure. Computer assisted analysis was performed using SPSS 17.0 (SPSS Inc., Chicago, IL, USA) statistical software after collation of data.

 RESULTS



The mean maternal age was 29.0 ± standard deviation (SD) 4.81 (range 18-40). One hundred and nine-term live-born singleton infants delivered at UDUTH and Federal Medical Center Birnin Kebbi during the study period had undergone ultrasound EFW <7 days preceding birth. The mean actual birth weight within the study cohort was 3.4 ± 0.518 (2.0-4.0 kg). 12 (10.7%) infants weighed <2500 g, and 83 (74.1%) weighed <2.6-4.0 kg. Of the 109 14 (12.5%) weighed >4.5 kg. The mean estimated fetal weight was 3.3 ± SD 0.415 (range of 2.3-5.0 kg). The mean estimated gestation age was 1.99 ± SD 0.166 (range 30-42). The accurate birth weight was seen in only 4.5% of the fetuses.

Twenty-one (19.3%) fetuses were identified as male while 38 (34.9%) was identified as female during the ultrasound examinations. In about 40 (36.7%) of the fetuses, the gender was not seen. Ultrasound image showing phallus as an echogenic cylindrical structure as the male gender in [Figure 1]. Ultrasound image showing presence of two oblong echogenic structures as female gender in [Figure 2]. [Table 1] shows error estimation, while [Table 2] shows maternal and infant demographics. [Table 3] shows mean error in birth weight prediction. [Table 4] shows ultrasound fetal sex versus fetal sex at birth cross Tabulation. {Figure 1}{Figure 2}{Table 1}{Table 2}{Table 3}{Table 4}

 DISCUSSION



The EFW is a very important component in order to correlate factors for the management of labor, delivery, and many decisions are influenced by this measurement, especially fetuses in breech presentation or suspicious of having macrosomia. As fetal weight cannot be measured directly, it must be estimated from fetal or maternal anatomic characteristics and until now the clinical and sonographic estimation [7],[11],[12],[13],[14],[15],[16],[17],[18],[19] are the only two worldwide methods used in many centers. A variety of formulas and parameters have been correlated with fetal weight. [6],[20],[21],[22] Among them, the Shepard formula, which includes BPD and AC, [23] and the Hadlock formula using FL and AC [8] are widely accepted and commonly used for EFW. These parameters are considered to be more accurate and simpler than others. [24],[25],[26] The results from combining all three parameters (BPD, FL, and AC) for predicting fetal weight appear to be controversial in the literature. Hadlock et al.[27] and Rose and McCallum [28] found that combining all three of these parameters produced more accurate results than the use of only two parameters, but Woo and Wan [29] conversely found no improvement in predictive accuracy over that of formulas using two parameters. In our study, we used the combinations of three parameters in the fetal weight estimation.

Accurate EFW has been shown to reduce perinatal morbidity and mortality associated with high-risk pregnancy such as intrauterine growth retardation, macrosomia, and prematurity. [30] Therefore, precise EFW is a very important valuable tool for determining further prenatal and obstetrics management. In most of our hospital routine, fetal weight estimation is not usually carried out unless there are some suspected clinical indications like fetal macrosomia, breech presentation, diabetes, trial of labor and twins. With the introduction of real-time ultrasound, it has enabled the clinician to reproducibly and accurately measure the fetal structure.

Our study shows that the mean error in the estimation of birth weight was 3.2 kg. In 39.3% of the cases, fetal ultrasound overestimated the birth weight, while in the average the ultrasound overestimated the weight by 3.46 kg. Fetal ultrasound underestimated the birth weight in 60% of the cases, with average underestimation of the birth weight by 3.08 kg. In a study done by Colman et al. [31] the actual birth weight was 3.33 kg (1.62-5.8 kg), in contrast to our study in which the actual birth weight was3.4 ± 0.518 (2.2-5.0 kg).In another study by Akinola et al. [32] the actual range of birth weights was (2.50-4.70 kg), with a mean of 3.39 kg ± SD 0.381, these results are similar to our findings. The similarity in results may be due to the fact that both are local studies done in Nigeria. Eighty-three infants (76%) weighed more than 2.5 kg, and 14 (13%) weighed <4.0 kg. These findings are similar to Colman et al. in their series of 20,469 infants. [31]

Ultrasound measurements give the appearance of precision, but the accuracy of ultrasonic estimations of fetal weight are limited by the fact that the mature fetus is an irregular, three dimensional structure of varying density, the weight of which cannot be calculated with certainty from biometric measurements. [33] [Table 3] shows mean error in birth weight prediction. It is therefore not surprising that the Australasian Society for Ultrasound in Medicine states that "No formula for estimating fetal weight has achieved an accuracy which enables us to recommend its use," [34] despite the large number of formulae available. [1],[35] This limitation could also account for the differences in the birth weights in this study and other previous studies. In a retrospective study, one can use the actual birth weight as the independent variable but is less useful clinically, because the birth weight is unknown until after birth. Chien et al.[36] has assessed the concordance between the estimated fetal weight (EFW) and the birth weight using the Bland and Altman [37] limits of agreement method. This method separates systematic bias effect of the measurement method from random error. However, the results from this study can be extrapolated only to obstetric populations with newborn birth weight 2.2-5.0 kg.

Thus, from this study and all the available published data, one can conclude that ultrasound has such a high estimation error. Therefore, depending only on the fetal ultrasound weight estimation may lead to unnecessary obstetrical interventions. The ultrasound findings need to be correlated with the physical examination to estimate birth weight because ultrasound measurements are operator dependent. So the high percentage of error in the estimation of the fetal weight may stem from the operator dependence.

Ultrasound can also be used to determine fetal gender as early as the first trimester using three dimensions imaging technique. [38],[39] With commonly available real-time ultrasound, fetal sex can be determined with some degree of certainty as from 16 th weeks and by 20 th weeks the accuracy is close to 97%. [40],[41]

From one hundred and nine fetuses included in the analysis, US finding showed that 21 (19.3%) were definitely male and all were confirmed to be so at birth, 38 (34.9%) were definitely female and all were confirmed to be female at birth. Probably female were 5 (4.6%) out of which were (40%) of whom were confirmed to be female at birth, and the probably male 3 (60.0%) were confirmed male at birth. US determined probably male were higher than probably female cases. This could be as a result easy identification of the scrotal sac in the perineum or if the fetus is in breech presentation or if there is excessive movement of the fetus. The criteria used for probably female was absence of two oblong echogenic structures called labia folds separated by an echo-free area doesn't mean simply female. This goes against a study done by Stocker while being consistent with that of Joseph Woo. [11],[42],[43] The scrotum may hide above or below the premium and may not be seen. The total confirmed actual fetal genders obtained from the mothers were 73 (67.0%) female and 36 (33.0%) males.

In this study, 40 (36.7%) of the cases, fetal sex was not determined by ultrasound. This happens when good view of the perineum is not seen, and this is also consistent with other similar studies. [11] The ability to assign gender increased with increasing gestational age and majority of our patients are in the third trimester. That is consistent with other studies done by Plattner and Whitlow. [43],[44],[45]

Other factors that can increase higher accuracy of fetal sex determination adequate amniotic fluid. Sifrash and Hirut [11] in their study shows that deepest pocket above 5 cm that was 94.8% accuracy, and for the deepest pocket below 5 cm it was 89.8%. [46] In our study presentation, placental position as well as amniotic fluid index was not taken into consideration for sex determination, this might be one our limitation. Accuracy also varies with technical factors, e.g., fetal position, machine use, maternal body habitus and operator skill. [47]

The social implications of antenatal gender identification are also very important. In developed countries, it has been shown that the majority (74.7%) of women are in favor of knowing the ultrasonographic interpretation of fetal gender and the accuracy rate at the 20-week scan is around 97%. [43] However, in developing countries, fetal gender should not be examined as a matter of routine, because of the lack of skilled/available manpower, making routine fetal gender determination impractical. [40] Maaji et al. [48] shows that about 6% of their study population declined to know fetal gender at ultrasound scan when asked by the sinologist. The main reason was that they were satisfied with whatever fetal gender that was present.

 CONCLUSION



There was a significant error seen while estimating fetal weight by ultrasound and underestimation has the highest percentage. However for accurate detection of fetal weight scan delivery interval is the most important factor. Depending only on the fetal ultrasound for the EFW can lead to unnecessary obstetric interventions. It is thus necessary to correlate the ultrasound findings with clinical findings.

Determination of fetal sex with ultrasound show some degree of accuracy in our study, and it should be recommended only if the mother requested for the gender during the scanning taking into account the social implications. To assess the different contributing factors for accurately in determining the fetal sex the fetal presentation, adequate amniotic fluid and placental position among others has to be taken into consideration.

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