CC BY-NC-ND
0Egyptian Journal of Forensic Sciences (2012) 2, 11-17
ORIGINAL ARTICLE
Cross sectional study to determine gestational age by metrical measurements of foot length
B. Manjunatha *, M.D. Nithin, Sasidharan Sameer
Department of Forensic Medicine and Toxicology, J.S.S. Medical College, Sri Shivarathreeshwara Nagar, Bannimantap, Mysore 570015, Karnataka, India
Received 16 September 2011; revised 29 October 2011; accepted 16 November 2011 Available online 14 January 2012
KEYWORDS
Gestational age; Foot length; Foetus; Infants;
Forensic anthropology; Determination
Abstract Gestational age estimation is essential in certain condition while performing foetal or neonatal autopsy. This study was conducted to assess the gestational age by foot length of foeti. Foot lengths of 126 foeti (77 live and 49 dead) were included in this study. The objective of this study was to assess the accurate gestational age by simple, non-invasive and economical method. The foot length was measured using vernier caliper between the posterior aspect of the heel to the tip of the longest toe. It was observed that there was an increase of 4.11 gestational weeks for increase in 1 cm of foot length. The results were encouraging and comparable with other similar studies. The foot length (independent variable) is strongly related with the period of gestation. As this method is simple, economical and accurate it can be used by a basic medical doctor and also paramedical even in a rural setup.
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1. Introduction
India does not recognize infanticide as a separate crime, nor is there any separate provision for it in the I.P.C. comparable to
* Corresponding author. Mobile: +91 9448208944; fax: +91 821 2493819.
E-mail address: manjunatha17@yahoo.com (B. Manjunatha).
2090-536X © 2011 Forensic Medicine Authority. Production and hosting by Elsevier B.V. All rights reserved.
Peer review under responsibility of Forensic Medicine Authority. doi:10.1016/j.ejfs.2011.11.003
the Infanticide Act of England 1938, where infanticide means unlawful killing of infant under the age of one year.1 'Infanticide' is a general term used for child murder. 'Filicide' refers to cases in which the murderer is the parent of the victim.2 In United Kingdom, infanticide is clearly distinguished from murder, especially if the infant is killed by the mother herself. She may be punished for being guilty of manslaughter and not murder. The law appears to assume a physiological basis for diminished responsibility in this context.3 In India, so much latitude is not extended to the mother, even though she might be suffering from some puerperal mental agony after child birth.4 The Indian law is very rigid and infanticide is punishable u/s 302 I.P.C. i.e., infanticide is not differentiated from murder in In-dia.5 Many studies6-10 have been done on determination of sex and stature by hand and foot length dimensions showing these indices to be poor indicators with limited practical value.
In this study, metrical measurement of foot length is used for estimating the gestational age, as it is a simple and
non-invasive technique. It can be carried out by a doctor even with a basic medical qualification.
2. Materials and methods
This study was conducted in the District Hospital, Belgaum, with the assistance of the Department of Obstetrics and Gynecology, Jawaharlal Nehru Medical College, Belgaum. A total of 126 cases were included in this study, of which 77 were live and 49 were dead. Out of 77 live preterm infants: 63 foeti were obtained from preterm deliveries and remaining 14 from lower caesarian section. Out of 49 dead foeti that were obtained from abortion, most were due to medical causes like ante partum haemorrhage, hypertension, etc. and two from abortion due to trauma. Eleven foeti were obtained from pre-term deliveries. In this study also all live infants and dead foeti were examined within 48 h after being, expelled or extracted.11 In this study, in most of the cases, only mothers consent was obtained due to nonavailability of the other parent during the examination. Staff in charge was requested to give consent for examination in such cases where parents had left behind the dead foeti.
Gestational age estimated by clinical examination was noted. General physical examination of foetus was done looking particularly for the presence of vernix caseosa in the folds, presence and distribution of lanugo hair and development of external genitalia.
2.1. Foot length
As, there was no statistical difference between right and left foot lengths, all measurements were done on right side.
Foot length measurements were done using a vernier caliper within 48 h after the foetus/infant being born, expelled or extracted. Vernier caliper used was of sliding type, graduated in centimetres up to 12 cm.
Foot length was measured between posterior aspect of the heel and tip of the longest toe, which may be the big toe or the second toe.12'13
3. Results
Statistical abbreviations:
4. Statistical analysis
Statistical analysis was done using the Statistical Package for Social Service (SPSS Plus) software on the computer.
Multiple R R2 Adjusted R2 Standard error .98824 .97661 .97642 .77735
DF Sum of squares Mean square
Regression 1 Residual 124 3128.78516 74.92913 3128.78516 .60427
4.1. Analysis of variance
F = 5177.81779, Sig. F = .0000
Variable b SE b Beta T Sig. T
FL 4.115765 Constant 5.607607 .057198 .988237 .354420 71.957 .0000 15.822 .0000
4.2. Variables in the equation
The above analysis shows the relationship between reported period of gestation and foot length. The correlation coefficient (R) is 0.988 indicating a positive correlation. P is <0.001 and standard error of correlation coefficient is 0.05, which is statistically significant.
Gestational age (GA) can be calculated using the formula GA = b x FL + K. In the present study,
GA = 4.11 x FL = 5.60 5. Discussion
In the present study, foot length in cm (FL) of 126 cases both live preterm infants and dead foeti were recorded. The reported period of gestation ranged between 24 and 36 weeks. Using linear regression analysis, regression coefficient (b) and constant (K) were estimated with gestational age as the dependent variable and FL as independent/explanatory variable. Gestational age (GA) can be estimated using the formula:
GA = b x FL + K
When graphs were plotted with gestational age as X axis and mean values of foot length as Y axis separately, a linear association was obtained (Fig. 1 and Table 1).
Reported period of gestation in weeks (RPG)
Figure 1 Linear relationship between reported period of gestation (RPG) and foot length (FL) in the present study.
RPG reported period of gestation in weeks (dependent variable)
FL foot length in cm (independent/explanatory variable)
R correlation coefficient
R2 extent of variation in dependent variable explained by the
changes in explanatory variable
DF degree of freedom
F variance ratio
b regression coefficient
K constant
SE b standard error of regression coefficient
T derived from Student's 'T test
Table 1 Relationship between reported period of gestation (RPG) and foot length (FL) in the present study.
RPG FL 24 25 26 27 28 29 30 4.41 4.61 4.96 5.21 5.6 5.9 6.07 32 34 6.31 6.47 35 7.08 36 7.56
The dependent variables FL are strongly related with the reported period of gestation, which has been brought out by high R and R2 values.
Hern estimated gestational age by using foot lengths of 1800 foeti ranging between 12 and 26 weeks of reported period of gestation.12 Mean values of foot lengths 24, 25 and 26 only were compared, as the period of gestation in the present study is between 24 and 36 weeks. Mean values of foot length obtained from the present study are slightly less when comparison was made Table 2.
A linear association is obtained on the graph in both the studies compared above, when foot length was plotted against gestational age Fig. 2.
Munsick studied 575 foeti with gestational age ranging between 9 and 20 weeks.14 Cases where reported period of gestation and estimated gestational age by clinical examination differed by >±2 weeks were not included which is the same exclusion criteria employed in the present study. Comparison of foot length with the present study was not possible as the gestational age ranges differ. However, we can compare statistical data like R2 value and P value. R2 value obtained from Munsick's study was 0.998 and in the present study is 0.976. R2 value indicates that 99% of variations in the gestational age are due to its relation with foot length in Munsick's study and it is 97% in the present study. R2 values obtained from both the studies are high. These high R2 values indicate that gestational age is strongly related to the foot length.
P value is less than 0.05 in both the studies (<0.002 in Munsick's study and <0.001 in the present study) which is statistically significant. As obtained in the present study, in Mun-
sick's study also a linear association is obtained on the graph when gestational age is plotted on X axis and foot length on Y axis (Fig. 3 and Table 3).
Mercer et al. obtained foot length of foeti from two different sources.15 203 post partum and 224 ultrasonographic measurements were made between 11 and 43 weeks of gestation. Since in the present study foeti of 24-36 weeks were studied, comparison of foot length obtained from both post partum and ultrasonographic measurements were compared with mean values of foot length from the present study. They compared favourably with each other.
R2 value obtained from Mercer's study was 0.98 and the present study yields a value of 0.97. R2 values obtained from both the studies are high and indicate a strong correlation between gestational age and foot length (Fig. 4 and Table 4).
Platt studied 120 patients with known menstrual dates.16 Ultrasonic measurements of foot lengths were made in foeti ranging between 12 and 28 weeks of reported period of gestation. Hence, comparison of mean values of foot lengths of 2428 weeks of gestation was possible with the present study. They compared favourably with each other R2 values in both these studies are high indicating a strong relation between ges-tational age and foot length; 0.94 and 0.97, respectively, for Platt's study and the present study. P values obtained from both the studies is less than 0.05 (less than 0.002 for Platt's study and less than 0.001 in the present study) which is statistically significant. Standard error of regression coefficient was 0.204 in Platt's study and 0.057 in the present study. Both these values are statistically significant (Fig. 5 and Table 5).
Goldstein used sonographic measurement of foetal foot length to assess the gestational age.17 The reported period of gestation ranged between 10 and 36 weeks. Among these, foeti of 24-36 weeks of gestation of Goldstein's study were compared with the mean values of foot length obtained from the present study. With gestational age as X axis and mean values of foot length as Y axis are plotted on a graph, linear association is obtained in both the studies (Fig. 6 and Table 6).
Table 2 Mean values of foot length in cm and reported period of gestation in weeks between Hern's study and present study.
RPG 24 25 26
Hern-FL 4.5 4.8 5.1
Present-FL 4.41 4.61 4.96
24 25 26
Reported period of gestation in weeks (RPG)
Figure 2 Comparison of mean values of foot length in cm against reported period of gestation in weeks between Hern's study and present study.
9 10 11 12 13 14 15 16 17 18 19 20
Reported period of gestation in weeks (RPG)
Figure 3 Linear relationship between reported period of gestation (RPG) and foot length (FL) in the study conducted by Munsick.
Table 3 Relationship between reported period of gestation (RPG) and foot length (FL) in the study conducted by Munsick.
RPG 9 10 11 12 13 14 15 16 17 18 19 20
FL 0.46 0.56 0.69 0.89 1.13 1.39 1.68 2.12 2.41 2.72 2.98 3.17
I Mercer -USG
24 25 26 27 28 29 30 31 32 33 34 35 36 Reported period of gestation in weeks (RPG)
Figure 4 Comparison of mean values of foot length in cm against reported period of gestation in weeks between Mercer's study ultrasound (USG) and post mortem (PM) and present study.
In Goldstein's study R value (correlation coefficient) was 0.90 and it is 0.98 in the present study. It can thus be inferred that in both the studies R value is high and that there is a definite positive correlation between foot length and gestational age. That is, with an increase in foot length there is an increase in gestational age and vice versa. P value in both the studies is <0.001, which is statistically significant. In both the studies gestational age can be calculated by using the following formula:
Gestational age(GA) = b (Regression coefficient)
x Foot length + K(constant)
In Goldstein's study,
GA = 3.87 x Foot length + 8.29
In the present study,
GA = 4.11 x Foot length + 5.60
Kumar and Kumar studied a total of 108 healthy human foeti of various age groups ranging from 14 to 36 weeks of gestation.13 They used foot length for assessing the gestational age. The mean values of foot length derived from the study conducted by Kumar and Kumar were compared with the mean values of foot length obtained from the present study. Foot lengths of both the studies compared favourably with each other (Table 7).
-Platt-FL -Present-FL
24 25 26 27 28
Reported period of gestation in weeks (RPG)
Figure 5 Comparison of mean values of foot length in cm against reported period of gestation in weeks between Platt's study and present study.
Table 5 Mean values of foot length in cm and reported period of gestation in weeks between Platt's study and present study.
RPG 24 25 26 27 28
Platt-FL 4.55 4.86 5.16 5.47 5.78
Present-FL 4.41 4.61 4.96 5.2 5.61
24 25 26 27 28 29 30 32 34
Reported period of gestation in weeks (RPG)
Figure 6 Comparison of mean values of foot length in cm against reported period of gestation in weeks between Goldstein's study and present study.
Table 4 Mean values of foot length in cm and reported period of gestation in weeks between Mercer's study ultrasound (USG) and post mortem (PM) and present study.
RPG 24 25 26 27 28 29 30 31 32 33 34 35 36
Mercer USG 4.4 4.7 5.1 5.4 5.8 5.7 6.1 6.2 6.3 6.7 6.8 7.1 7.4
Mercer PM - 4.8 - 5.2 5.6 5.7 6 6 6.6 6.8 7.1 7.2 7.4
Present - FL 4.4 4.6 4.9 5.2 5.6 5.8 6 - 6.3 6.7 7 7.5
Table 6 Mean values of foot length in cm and reported period of gestation in weeks between Goldstein's study and present study.
RPG 24 25 26 27 28 29 30 32 34 35
Platt - FL 4.6 4.7 4.7 5 5.3 5.2 6.1 5.9 6.5 7.1
Present - FL 4.4 4.6 4.9 5.2 5.6 5.8 6 6.3 6.7 7
Table 7 Mean values of foot length in cm and reported period of gestation in weeks between Kumar and Kumar's study and present study.
RPG 24 25 26 27 28 29 30 32 34 35
Platt - FL 4.6 4.7 4.7 5 5.3 5.2 6.1 5.9 6.5 7.1
Present - FL 4.4 4.6 4.9 5.2 5.6 5.8 6 6.3 6.7 7
Reported period of gestation in weeks (RPG)
Figure 7 Comparison of mean values of foot length in cm against reported period of gestation in weeks between Kumar and Kumar's study and present study.
A linear association was obtained when foot length was plotted against gestational age, which is similar to the linear curve obtained in the present study (Fig. 7).
When the statistical data of present study is compared with those of Kumar and Kumar following inferences were drawn.
A very high R and R2 were obtained in both the studies. They were 0.98 and 0.97 for the present study and Kumar and Kumar's study, respectively. High R and R2 values indicate a strong relation between gestational age and foot length. A statistically significant P value of <0.001 was derived from both the studies. Gestational age can be calculated using the following formula:
Gestational age = b (Regression coefficient)x Foot length
+ K(constant) In Kumar and Kumar's study, Gestational age = 3.48 x FL + 8.86 In the present study,
Table 8 Comparison gestational age estimated by different workers in the same case of a foetus.
Name of workers (s) Amato et al. Mercer et al. Gestational age (estimated) 23.71 25.04 Kumar and Kumar 25.07 Goldstein 26.32 Present 24.72
27 26.5 26
< 25.5 tí
■S 25
24 23.5 23 22.5 22
Amato et al
Mercer et al
Kumar & Kumar
Name of Worker(s)
Goldstein
Figure 8 Comparison of gestational age estimated by different workers using foot length in the same case of a foetus.
Gestational age = 4.11 x FL + 5.60
Huxley reports a case history where a partially macerated foetus was submitted to the Human Identification Laboratory at the University of Arizona for the purpose of determination of gestational age.18 He tried to calculate the gestational age from foot length using formulae derived from four workers. They were Mercer et al. (1987), Goldstein et al. (1988), Amato et al. (1991) and Kumar and Kumar (1993). Using four different formulae, gestational age of the foetus determined was estimated to be in the range of 23.71-26.32 weeks. When the formula derived from the present study was applied, the gesta-tional age of that foetus was estimated to be 24.72 weeks, which falls well within that range.
Table 8 and Fig. 8 show comparison between the present study and other four studies used in that case.
6. Summary
This study was conducted in District Hospital, Belgaum, in the year 1997-1998. It was a cross-sectional study (not involving follow-up of the cases), where gestational age was estimated using the foot length. Measurements of 126 cases (both live and dead) were included in this study. Reported period of gestation, considered in this study was in the range of 2436 weeks. Measurements of both live and dead cases and of either sex were combined as no statistical difference was found. Foot length measurements were obtained using a vernier caliper.
Applying regression analysis, statistical date was derived. Statistical values like R (correlation coefficient) and R2 (extent of variation in gestational age which is explained by changes in foot length) were high, indicating a strong relation between gestational age and foot length. Tests of significance like,
(1) 'F test,
(2) Student's ' T test,
(3) ' P' value and
(4) standard error of regression coefficient
were all found to be statistically significant.
A linear association was obtained when mean values of foot length were plotted against gestational age on a graph.
Applying, the statistical data derived from foot lengths, ges-tational age can be calculated using the formula:
Gestational age = b (Regression coefficient)x Foot length
+ K(constant)
The findings and results of this study are well supported by similar studies by other workers. Only a slight discrepancy was found when mean values of foot length of the present study
was compared with those of western workers. That is, mean values of foot length of the present study were marginally less. This difference can be explained by variations in socioeconomic status, environmental and nutritional factors.
7. Conclusion
Establishing precise duration of pregnancy is of paramount importance for a forensic pathologist. Foot length of both live preterm infants and dead foeti has shown a high correlation with gestational age, which reflects the accuracy of this study.
It is a non-invasive technique. There is no need for any special training to calculate gestational age by this method, as the methodology is simple. As the expenditure involved in this study is minimal it can be considered as an economical one and be used in rural areas by doctors with basic medical qualification. Another advantage of this study is that it is not lengthy and time consuming. This study can also be of help in cases where only fragmented remains of foetus are available, where other parameters like crown heel length, weight, etc. cannot be applied. In most of the cases it is unlikely to have both feet destroyed either due to extraction of foetus during delivering/abortion or due to attack by carnivorous animals. Out of the various parameters available to assess the gestational age, this appears to be equally accurate, less tedious and there is availability of at least one foot, either right or left side if the other side is mutilated for the reasons already explained.
Enough work has been made by many workers and the accuracy and its benefits have been already highlighted. Many workers are of the opinion that it is very practical and reliable. It is felt that this technique must be popularized by using it more frequently in day to day practical work.
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Gestational age can be calculated using the formula: Gestational age = b(Regression coefficient)x Foot length+ K(constant) In Goldstein's study,
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