Tropical Journal of Obstetrics and Gynaecology

: 2018  |  Volume : 35  |  Issue : 1  |  Page : 63--67

Evaluation of gestational age by fetal occipitofrontal diameter in second and third trimesters of pregnancy in Sudanese women

Rehab Hussein1, Moawia Bushra Gameraddin2, Bushra Hussein A Malik3, Mohamed Yousef4, Qurain Turki3,  
1 Department of Radiology, Najran University, College of Applied Medical Science, Najran, Saudi Arabia
2 Department of Diagnostic Radiologic Technology, Faculty of Applied Medical Sciences, Taibah University, Almadina Al-Monawarah, Saudi Arabia
3 College of Medical Applied Science, University of Hail, Hail, King, Saudi Arabia
4 Department of Radiological Science, Batterjee Medical College, Jeddah, Saudi Arabia

Correspondence Address:
Dr. Moawia Bushra Gameraddin
Department of Diagnostic Radiologic Technology, Faculty of Applied Medical Sciences, Taibah University, Al-Madinah Al-Munawarah
Saudi Arabia


Background and Objective: The accurate gestational age (GA) is critically important for pregnancy management, particularly for determining viability and growth in premature labor. The aim of this study was to evaluate the usefulness of occipitofrontal diameter (OFD) in estimation of GA in the second and third trimester of pregnancy. Materials and Methods: In this cross-sectional prospective study, a total of 483 Sudanese pregnant women underwent the routine sonographic examination at different antenatal care centers in Khartoum state using curvilinear transducers 3.5 MHz. The fetal OFD, biparietal diameter (BPD), and femoral length (FL) were measured and correlated with GA. Equations were obtained from regression models to estimate the GA. Results: In total, 384 singleton fetuses ranging between 12 and 40 weeks of gestation were enrolled. A statistically significant and strong relationship was found between OFD and GA, R2 = 0.85. The model regression of OFD, BPD, and FL produced together with an accurate equation to estimate GA in second and third trimester with the equation; GA (weeks) = 4.474 + 100 × BPD + 0.118 × OFD + 0.128 FL (r = 0.909, n = 384, SE = 2.271). The equation of GA from OFD alone was GA = 3.663+.286 × OFD with SE = 2.882. The OFD can be used as a single lone parameter in the estimation of GA to give an accuracy of SE ± 2.882 days, but when used in combination with the other two parameters, the accuracy increased to SE ± 2.770 days. Conclusion: Fetal OFD assessed by sonography may serve as a useful parameter in determining GA and evaluating fetal growth in the second and third trimesters of pregnancy.

How to cite this article:
Hussein R, Gameraddin MB, A Malik BH, Yousef M, Turki Q. Evaluation of gestational age by fetal occipitofrontal diameter in second and third trimesters of pregnancy in Sudanese women.Trop J Obstet Gynaecol 2018;35:63-67

How to cite this URL:
Hussein R, Gameraddin MB, A Malik BH, Yousef M, Turki Q. Evaluation of gestational age by fetal occipitofrontal diameter in second and third trimesters of pregnancy in Sudanese women. Trop J Obstet Gynaecol [serial online] 2018 [cited 2023 Oct 1 ];35:63-67
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Full Text


The accurate determination of gestational age (GA) is important for pregnancy management and determining viability in premature labor and postdates deliveries.[1] Valid GA is very important in the management of high-risk pregnancies and in cases where termination is necessary.[2] Accurate knowledge of fetal GA is fundamental throughout pregnancy. Thus, error in the GA estimation can result in fetal prematurity and postmaturity. Extremes of fetal growth contribute disproportionately to the overall perinatal and infant morbidity and mortality.[3],[4]

Ultrasound is a reliable imaging modality in the assessment of pregnancy as it allows real-time visualization and evaluation of fetal and maternal structures.[5] GA estimates by last menstrual period (LMP) and ultrasound have been correlated.[6] A variety of measurements have been suggested to establish and measure the GA.[2],[5] In second and third trimester, biparietal diameter (BPD), femoral length (FL), head circumference (HC), and fetal weight (FW) have been commonly used to assess GA.[7] In the most recent studies, BPD, FL, and head circumference (HC) were used to estimate GA, although some studies reported that they were less accurate after 26 weeks of gestation.[8] However, we did not find studies demonstrating the accuracy of occipitofrontal diameter (OFD) in the estimation of GA.

In the current study, it was observed the OFD bears a strong linear correlation with FL and BPD. From this correlation, we constructed regression models to estimate the GA. In previous studies, the OFD represented an important fetal biometric parameter to determine the cephalic index (CI), which is a significant factor to detecting deformities of fetal head shape such as dolichocephaly and brachycephay.[9],[10] The OFD is a function of HC, and it is easily and rapidly measured at the same level of BPD. However, the different fetal presentations are not always favorable for BPD assessment, and because the fetus sometimes faces its placenta, the fetal head position becomes in OF position. This needs difficult maneuver to establish an accurate BPD measurement. Some previous studies proposed that the fetal presentation is significantly influenced by placenta localization.[11],[12] For this reason, and in these occasions, OFD represent an accurate fetal biometry for estimating the GA.

The aim of this study was to evaluate the usefulness of OFD to estimate the GA to construct a nomogram of OFD in second and third trimesters of pregnancy for the local population. This may be useful to assess the GA when the duration of pregnancy is unknown.

 Materials and Methods

This was a cross-sectional study conducted from March 2013 up to April 2016 in Khartoum state. A total of 483 Sudanese pregnant women were selected using convenient sampling. The sonographic examination was performed by expert Sonologists and Obstetricians. Every pregnant woman was scanned six times (3 scans/semester). Interobserver error was considered. Means and standard deviations of fetal biometrics (OFD, FL, and BPD) were calculated and stored for comparison.

The participants were certain about the date of their last menstrual period (LMP) and underwent routine sonographic examination for antenatal care. The study was conducted at different antenatal care Centers in Khartoum State (Capital of Sudan) which lies in central Sudan and provides basic health care in the country. Informed consent was taken from the participants. The study was approved by the ethical committee of the Alzaiem Alazhari University.

The sonographic procedure

Ultrasound investigation was done early at four and five weeks of gestation for all the participants to confirm the accurate date of the pregnancy. The participants were scanned in the supine position with the ultrasound machine using 3.5 MHz curvilinear transducers. A standard ultrasound machine was utilized for the investigations called SONOACE-CONVEX ARRAY CA, version LOGIQ 9.

The OFD was measured perpendicular to the falx cerebri at the midline at the widest region of the hemispheres of the fetal brain. The posterior horns of the lateral ventricles, hypothalamus, and the cavum pellucidum are visible at this level, and the head is typically oval in shape. The intersection of the calipers was placed on the outer border of the occipital thinner side of skull table (occipitofrontally) at the longest part of the skull. At this level, the image was saved [[Figure 1]. The measurement of OFD was repeated, and the average was taken. To achieve this, an axial view of the fetal head at the level of the thalami was taken as close as possible to the horizontal [Figure 1]. Measurements of BPD were taken perpendicular to the OFD. Then measurement of the FL was also acquired in the same obstetrical manner [Figure 2].{Figure 1}{Figure 2}

The inclusion criteria included normal Sudanese pregnant women in second and third trimester with normal singleton pregnancy and known last menstrual period. The exclusion criteria were multiple pregnancies, pregnancies with confirmed congenital abnormalities, pregnancies complicated by hypertension and preeclampsia, maternal diabetes mellitus, and chronic maternal diseases.

Statistical analysis

The data were analyzed using statistical software program (SPSS, version 16, Chicago, USA). Quantitative data were described as means ± standard deviation. Pearson correlation test was used to find correlation of GA with the fetal biometrics (OFD, FL, and PBD). Linear quantitative regression analysis was used to derive models for estimation of GA from OFD, FL, and BPD.


A total of 384 normal singleton pregnant women were recruited. The mean and standard deviation of their age and parity were 30.6 ± 7.52 years and 1.6 ± 0.49, respectively. It was found that the OFD was not significantly correlated with maternal age, maternal body mass index (BMI) and parity (P values = 0.13, 0.26, and 0.69, respectively), as shown in [Table 1]. The fetal biometric BPD, FL, and OFD were measured from all participants, as shown in [Figure 1] and [Figure 2]. The GA is plotted against OFD, as shown in [Figure 3]. A linear correlation was observed between OFD and BPD and FL [Figure 4] and [Figure 5].{Table 1}{Figure 3}{Figure 4}{Figure 5}

GA was strongly correlated with OFD, BPD, and FL with R = 0.92, 0.93, and 0.92, respectively, as shown in [Table 2]. The addition of OFD to FL and BPD provides stronger correlation than the other parameters alone (R = 0.95). Sets of equations were obtained from regression models to estimate the GA from fetal biometrics: OFD, BPD, and FL. [Table 3] reveals a nomogram which was constructed for estimating the GA (weeks) from OFD (mm) at 12 to 40 weeks of gestation.{Table 2}{Table 3}


This was one of the few studies that demonstrated the accuracy of OFD in the estimation of the GA in second and third trimesters of pregnancy in our country. Accurate estimation of GA is a key issue in pregnancy.[13] The OFD is one of the important fetal biometrics that is used to measure GA and fetal weight. It is a function of HC and is easily and rapidly measured at the same level at which the BPD is measured. In the present study, we formulated a set of equations obtained from regression models of OFD, FL, and BPD to estimate the GA. We also constructed regression equations that can be used to determine the GA in the second and third trimesters of pregnancy.

Snijders et al.[14] studied the measurements of BPD and OFD. For each of the measurements, regression analysis was applied examining linear, quadratic, and cubic models for association with GA, the standard deviation of the OFD increased with GA. Such findings were reported by Juozas et al.[15] These findings supported our results. We found a direct proportionality linear relationship between OFD and GA estimated by LMP, BPD, and FL.

In the current study, the fetal biometric parameters (BPD, FL, and OFD) were measured in 384 normal pregnancy cases. We observed that OFD has a strong linear correlation with BPD and FL. We also noticed that by FL alone the GA was estimated with SE of 2.770 days and the SE of OFD was 2.882. However, the difference between FL and OFD is not high. This supported the accuracy of OFD which is approximately close to FL. In a previous study, the OFD was used in combination with BPD, FL, and mean abdominal diameter (AD). It provided an accuracy of estimated GA with an SD of 2.2 days.[14],[16] This supported our findings.

In the study, we found a strong linear correlation between the mean of LMP with BPD, FL, and OFD. The highest correlation coefficient was observed between LMP and femur length (r =0.953). This result is consistent with Peter et al. who reported a strong correlation of LMP with FL (r = 0.946).[17] Moreover, it was found that there is a direct proportionality linear relationship between GA and OFD with linear correlation of. 924. When OFD was used for calculating the GA alone, the model regression equation was GA = 3.663 +.286 × OFD with standard error (SE) =2.882. It revealed a strong linear correlation. This finding agreed with Blaas et al. who reported a significant linear correlation of OFD with LMP.[18] When all the three parameters (FL, BPD, OFD) were incorporated the accuracy was improved (SE = 2.271), and the linear correlation increased (r = 0.90). Therefore, the combination of OFD with BPD and FL provided a better accurate estimation of GA in second and third trimesters. This finding agreed with Abuzeed et al.[19] who estimated the GA from OFD.

Moreover, using the equation: GA = 4.474 +.100 × BPD +.128FL +.118 × OFD. With SE of 2.270 to estimate the GA provides a considerable improvement of estimation. However, according to these findings, the high accuracy of estimating GA can be obtained by the combination of FL, BPD, and OFD. Therefore, the addition of OFD to FL and BPD provides better accuracy for the determination of GA.

Our results took into account the inaccuracy of GA estimation at the end of the third trimester due to biological variability of fetal growth and maternal ethnicity that may lead to errors of fetal measurements with advancing GA.[20],[21]


OFD is an important accurate fetal biometric parameter. There was a linear relationship and strong correlation of OFD with FL, BPD, and GA. The regression models of OFD with a combination of BPD and FL provides an accurate prediction of GA more than using BPD and FL alone. We constructed a nomogram for OFD at second and third trimesters of pregnancy for the local Sudanese population. This nomogram may be useful to assess GA when dates of the pregnancy are unknown.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.


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