- Email: [email protected]
Relationship between the tensile strengths and diameters of human umbilical cords
Journal of Forensic and Legal Medicine 56 (2018) 48–50
Contents lists available at ScienceDirect
Journal of Forensic and Legal Medicine journal homepage: www.elsevier.com/locate/yjflm
Relationship between the tensile strengths and diameters of human umbilical cords
T
D.M.G. Fernandoa, S.M.K. Gamageb,∗, S. Ranmohottigea, I. Weerakkodya, H. Abeyruwanc, H. Parakramac a
Department of Forensic Medicine, Faculty of Medicine, University of Peradeniya, Sri Lanka Department of Anatomy, Faculty of Medicine, University of Peradeniya, Sri Lanka c Department of Civil Engineering, Faculty of Medicine, University of Peradeniya, Sri Lanka b
A R T I C LE I N FO
A B S T R A C T
Keywords: Umbilical cord tensile strength Diameter of umbilical cord Weight per unit length of umbilical cord Precipitate delivery Breaking point of umbilical cord
Mothers of alleged infanticides might claim that umbilical cord broke during precipitate delivery causing injuries detected on baby at autopsy. There is paucity of evidence regarding this possibility. The objective of the study was to determine relationship between tensile strength and diameter or weight per unit length of cord. Diameters and weights per unit length of fresh umbilical cords were determined. Tensile strengths were measured by Hounsfield Testing Machine. Relationship between tensile strength versus cord diameter and weight per unit length were analyzed. Of 122 cords, average tensile strength, diameter and weight per centimeter were 50.4 N, 7.73 mm and 6.87 g respectively. The tensile strengths were directly proportional to diameter. There was no association between tensile strength and weight per centimeter. Measurement of the diameter of cord is important during autopsy to predict tensile strength and thereby to presume whether cord could have broken by the weight of the baby.
1. Introduction It is a long believed concept that in precipitate deliveries, the umbilical cord could be broken by the weight of the neonate. Tensile strength (TS) is an important factor which determines the breaking point of umbilical cords (UC). Mothers accused of infanticide may claim that during precipitate delivery the umbilical cord broke by the weight of the baby, resulting in head injury, leading to death.1,2 This scenario has been experienced personally a couple of times by the principal investigator, in Sri Lanka and it is mentioned as a possibility in renowned text books such as Forensic Pathology by Bernard Knight, 4th Edition.2 In addition, the author of ‘Medicolegal aspects of injury’, LBL Alwis, supports the same fact, experienced during his practice in Sri Lanka.3 However, since this is not a scientifically well proven phenomenon and it is important to find out whether the weight of the neonate could actually exceed the TS of the umbilical cord. The human umbilical cord has an average weight of 15 g/10 cm and an average diameter of 1.5 cm. A literature search extending up to 1960 revealed only a few experimental articles on TS,4–7 and of those, most were for obstetric purposes. Only two studies were dealing with the forensic aspects. One
∗
had tested 38 cords in 1966 and found the average TS to be 5 kg with a range of 2–12 kg.6 The second study conducted in 2013, which is the latest, examined the tensile strengths of 25 UCs and has concluded that the average TS of UCs is 79 N.1 A study to simulate controlled cord traction gave 5.88 kg as the average TS with a range of 1.88 kg–10 kg.5 Human umbilical cord is elastic and will stretch up to 12.5% of its length.7 However, when the force exceeds the tensile strength, most umbilical cords have a tendency to break at a point within the first 30 cm of the fetal side of the cord.4,8 However, none of the articles provided strong evidence on the relationship between the TS of UC and their physical properties such as diameter and weight per unit length. Therefore our objectives were to determine the average tensile strength of human UC and to determine whether there is a relationship between the TS and cord properties such as diameter and weight per unit length. 2. Materials and methods 2.1. Consent, ethical approval and samples
Corresponding author. E-mail addresses: [email protected], [email protected] (S.M.K. Gamage).
https://doi.org/10.1016/j.jflm.2018.03.008 Received 22 September 2017; Received in revised form 6 February 2018; Accepted 5 March 2018 Available online 06 March 2018 1752-928X/ © 2018 Elsevier Ltd and Faculty of Forensic and Legal Medicine. All rights reserved.
Informed written consent from both parents and institutional ethical
Journal of Forensic and Legal Medicine 56 (2018) 48–50
D.M.G. Fernando et al.
approval was obtained prior to sample collection. Umbilical cords were collected from the labor room, Teaching Hospital, Peradeniya, Sri Lanka, from consecutive deliveries. Inclusion criteria were, normal vaginal vertex deliveries between 37 and 40 weeks of period of gestation; deliveries with neonates of birth weights from 2.5 to 3.5 kg and umbilical cords with normal lengths from 40 to 70 cm and with two arteries and one vein.9 Exclusion criteria were, cords of placentas with macroscopic evidence of inflammation and hyper or hypo coiling of cord. Umbilical cords were stored in physiological saline immediately after delivery to preserve the mechanical properties.10 They were either tested immediately or within 12 h after storing in 4 °C. The testing was performed at room temperature (23–32 °C). 2.2. Physical measurements of cords For each cord, the diameters were measured at three sites, i.e. the middle and 2 cm from each end, using a Vernier caliper with an accuracy of 0.1 mm. The sites of measurement of diameter were consistent in all cords. Weights and lengths were measured using an electronic scale and a steel tape with an accuracy of 0.1 g and 1 mm respectively.
Fig. 2. Tensile strength (N) of umbilical cords.
The line graph between the number of cords and tensile strengths (N) roughly resembled a normal distribution (Fig. 2) and the median value was 59 N (6.0 kg). Mean ± SD of TS was 56.3 ± 16.8 N and the average TS was 50.4 N (5.13 kg). The mean diameter of the cords was 7.7 mm. The increase in tensile strength was directly proportional to the diameter (Fig. 3). Average weight per length of the UCs was 6.8 g/cm. No clear relationship was discovered when TS of 98 cords were analyzed with regard to weight per unit length (Fig. 4).
2.3. Testing of tensile strength TS were measured at the Faculty of Engineering, University of Peradeniya, Sri Lanka with Hounsfield Testing Machine which is a computerized Universal Testing Machine with an accuracy of 0.1 N (Fig. 1). One end of the UC was wound around the pulley in the movable arm of machine and the edge of the cord was secured to the machine by tightening it to the arm via screw clips. The other end of the UC was attached to the fixed arm in the same manner and was secured to it by screw clips (Fig. 1). An increasing traction was applied at the rate of 50 mm/min, while a computer continuously generated a stress versus strain graph until the cord broke. The distribution of tensile strengths across the sample, relationship between TS versus umbilical diameter (mm), relationship between TS and weight per unit length of UC were analyzed using GraphPad Prism software.
4. Discussion There are two main occasions in which umbilical cords can break spontaneously. First is during standing and second is while getting up from squatting position.1 However, the force exerted on the cord should exceed the tensile strength of the cord for it to break in an anatomically normal umbilical cord. However, in instances with cord abnormalities, such as velamentous insertion of the cord and deficiencies of Wharton's jelly, easy rupture of the cord is possible.11 Tensile strength of the umbilical cord is the maximum stress the cord can withstand before breaking.4 It is the
3. Results A total of 200 cords were collected adhering to inclusion and exclusion criteria. Of these 51 UC that were too short to be affixed on the machine arms and 27 cords that broke at the pulley were excluded. The remaining 122 cords were tested for TS. The increase in tensile strength was directly proportional to the diameter. When TS of were analyzed with regards to weight per unit length, no clear relationship was discovered.
Fig. 1. Hounsfield testing machine and how the umbilical cords were attached to the fixed and movable arms.
Fig. 3. Tensile Strength (N) versus diameter (mm) of umbilical cords.
49
Journal of Forensic and Legal Medicine 56 (2018) 48–50
D.M.G. Fernando et al.
There were several limitations of the study. Impact of the jerk from baby falling down could not be considered because the Hounsfield machine applied controlled traction on cords and therefore it was not possible to simulate the sudden fall and jerk which actually would occur in precipitate deliveries. Difficulty for manual traction due to the slipperiness of the cord could not be considered as the cord ends were tightly anchored to machine arms. Tensile strengths of the cords could have been correlated with the weights and gestational age of babies, which will be considered in further studies. The height of the baby's fall would be another important factor to be considered. The possibility of the fetus impacting on the floor, without rupture of the umbilical cord, particularly in cases where the mother has a leg height less than the cord length, would be worthwhile considering in future studies. 5. Conclusions On the basis of our study, we would like to advice the forensic pathologists conducting the autopsy, to measure the diameter of the cord, since it correlates to the tensile strength of the cord. Furthermore the tensile strength can be estimated using our findings since it has a directly proportional relationship with the diameter. However the impact of the jerk from baby falling down, difficulty for manual traction from the slipperiness of the cord and maternal anatomical features should be further considered when assessing a cause of precipitous delivery.
Fig. 4. TS (N) versus weight (g) per unit length (10 cm).
highest point of the stress strain curve obtained from a tensile strength test. The average tensile strength of the umbilical cords of the present study was 51.3 N (5.2 kg). This value is higher than the mean tensile strength of the study by Morris et al., which is 49.03 N. However our value is much lower than the mean tensile strengths obtained in the two studies by Pommenich12 and Tantius,1 which are 73.55 N and 79.85 N respectively. Umbilical cords can have a range of tensile strengths due to differences in Wharton's jelly, collagen content and structure of smooth muscle layers of umbilical arteries.5 These physical properties of the umbilical cord may be genetically predetermined or dependent upon the sex, nutritional status and the well being of the fetus.7 Therefore the differences of tensile strength values concluded in the above studies may be attributed to the differences in the genetics, nutritional status and well being of different study population. Furthermore, differences in the experimental setup and the methods used to measure tensile strengths may have caused the observed differences of tensile strengths in the above studies. The diameters of the cords of the present study are directly proportional to the tensile strength. However, the study by Tantius et al. has not found such relationship between cord diameter and tensile strength.1 This may be explained by the sample number. Tantius et al. has used 25 umbilical cords, whereas this study examined 122 cords. Therefore we advocate the measurement of the diameter of the cord, as it can provide a guide to the tensile strength of the cord. However, the weight of the cord is not a reliable index to assess its TS. Out of the 122 cords only 7 (5.7%) had a TS less than 30 N (3.06 kg). The average weight of a newborn baby in Sri Lanka is 3.0 kg.13,14 Therefore, it may be presumed that unless the weight of the baby is greater than the average in Sri Lanka, it is unlikely that the cord will break, due to the baby's weight, except at instances in which there are cord abnormalities, which can affect the tensile strength, such as deficiencies in Wharton's jelly, funisitis and abnormal insertion of cord into the placenta etc. However other factors such as the jerk and the slipperiness of the cord need to be taken into consideration. The mother or some other person can break the cord manually, the slipperiness of the cord being the only difficulty.6 Knight B in 1996 recommends that the length and the severed ends of the cord should be examined during an autopsy on suspicious deaths of newborns.2 Macroscopic and microscopic examination of cords would help to differentiate between a cord which has been torn due to anatomical abnormalities or infection and a cord which has been torn or cut by the culprit.
Funding sources We did not receive any funding for this project. Conflicts of interest Authors declare that they have no conflicts of interests. The work has not been published elsewhere as a full article. Acknowledgements We acknowledge the labor room staff of Teaching Hospital, Peradeniya for the support given for sample recruitment. References 1. Tantius B, Rothschild MA, Valter M, Michael J, Banaschak S. Experimental studies on the tensile properties of human umbilical cords. Forensic Sci Int. 2014 Mar;236:16–21. 2. Knight B, Saukko P. Knight's Forensic Pathology. 4 ed. Florida: Taylor and Francis; CRC press; 2016. 3. de Alwis LBL. Medico legal aspects of Injuries. Colombo, SriLanka: Author; 2007. 4. Ghosh KG, Ghosh SN, Gupta AB. Tensile properties of human umbilical cord. Indian J Med Res. 1984 Apr;79:538–541. 5. Crichton JL. Tensile strength of the umbilical cord. Am J Obstet Gynecol. 1973;115(1):77–80. 6. Morris JF, Hunt AC. Breaking strength of the umbilical cord. J Forensic Sci. 1966 Jan;11(1):43–49. 7. Collins JH, ed. Silent Risk: Issues about the Human Umbilical Cord. 1 ed. USA: Xlibris Corporation; 2002. 8. Itskovitz J, Friedman M, Peretz BA, Brandes JM. Intrauterine rupture of the umbilical cord during delivery. Eur J Obstet Gynecol Reprod Biol. 1980 Jan;10(1):35–40. 9. Balkawade NU, Shinde MA. Study of length of umbilical cord and fetal outcome: a study of 1,000 deliveries. J Obstet Gynaecol India. 2012 Oct;62(5):520–525. 10. Schmidt W. The amniotic fluid compartment: the fetal habitat. Adv Anat Embryol Cell Biol. 1992;1992(127):1–100. 11. Rocha J, Carvalho J, Costa F, Meireles I, do Carmo O. Velamentous cord insertion in a singleton pregnancy: an obscure cause of emergency cesarean—a case report. Case Rep Obs Gynecol. 2012;2012:308206. 12. Pommenich C. Experimentelle Untersuchungen über die Zerreißfestigkeit der menschlichen Nabelschnur: Scheur. 1948; 1948. 13. Kumara DMA, Perera H. Evaluation of Six commonly used formulae for sonographic estimation of fetal weight in Sri lankan population. Sri lanka J Obstet Gynaecol. 2009;31:20–33. 14. Abeyagunawardena IA, Abeynayake A, Anuththara T, et al. Is it appropriate to use WHO Multicentre Growth Reference Study standards to assess the growth parameters of Sri Lankan babies?- A single centre cross sectional study. BMJ Paediatr Open. 2018;2:e000174http://dx.doi.org/10.1136/bmjpo-2017-000174M.
50
Contents lists available at ScienceDirect
Journal of Forensic and Legal Medicine journal homepage: www.elsevier.com/locate/yjflm
Relationship between the tensile strengths and diameters of human umbilical cords
T
D.M.G. Fernandoa, S.M.K. Gamageb,∗, S. Ranmohottigea, I. Weerakkodya, H. Abeyruwanc, H. Parakramac a
Department of Forensic Medicine, Faculty of Medicine, University of Peradeniya, Sri Lanka Department of Anatomy, Faculty of Medicine, University of Peradeniya, Sri Lanka c Department of Civil Engineering, Faculty of Medicine, University of Peradeniya, Sri Lanka b
A R T I C LE I N FO
A B S T R A C T
Keywords: Umbilical cord tensile strength Diameter of umbilical cord Weight per unit length of umbilical cord Precipitate delivery Breaking point of umbilical cord
Mothers of alleged infanticides might claim that umbilical cord broke during precipitate delivery causing injuries detected on baby at autopsy. There is paucity of evidence regarding this possibility. The objective of the study was to determine relationship between tensile strength and diameter or weight per unit length of cord. Diameters and weights per unit length of fresh umbilical cords were determined. Tensile strengths were measured by Hounsfield Testing Machine. Relationship between tensile strength versus cord diameter and weight per unit length were analyzed. Of 122 cords, average tensile strength, diameter and weight per centimeter were 50.4 N, 7.73 mm and 6.87 g respectively. The tensile strengths were directly proportional to diameter. There was no association between tensile strength and weight per centimeter. Measurement of the diameter of cord is important during autopsy to predict tensile strength and thereby to presume whether cord could have broken by the weight of the baby.
1. Introduction It is a long believed concept that in precipitate deliveries, the umbilical cord could be broken by the weight of the neonate. Tensile strength (TS) is an important factor which determines the breaking point of umbilical cords (UC). Mothers accused of infanticide may claim that during precipitate delivery the umbilical cord broke by the weight of the baby, resulting in head injury, leading to death.1,2 This scenario has been experienced personally a couple of times by the principal investigator, in Sri Lanka and it is mentioned as a possibility in renowned text books such as Forensic Pathology by Bernard Knight, 4th Edition.2 In addition, the author of ‘Medicolegal aspects of injury’, LBL Alwis, supports the same fact, experienced during his practice in Sri Lanka.3 However, since this is not a scientifically well proven phenomenon and it is important to find out whether the weight of the neonate could actually exceed the TS of the umbilical cord. The human umbilical cord has an average weight of 15 g/10 cm and an average diameter of 1.5 cm. A literature search extending up to 1960 revealed only a few experimental articles on TS,4–7 and of those, most were for obstetric purposes. Only two studies were dealing with the forensic aspects. One
∗
had tested 38 cords in 1966 and found the average TS to be 5 kg with a range of 2–12 kg.6 The second study conducted in 2013, which is the latest, examined the tensile strengths of 25 UCs and has concluded that the average TS of UCs is 79 N.1 A study to simulate controlled cord traction gave 5.88 kg as the average TS with a range of 1.88 kg–10 kg.5 Human umbilical cord is elastic and will stretch up to 12.5% of its length.7 However, when the force exceeds the tensile strength, most umbilical cords have a tendency to break at a point within the first 30 cm of the fetal side of the cord.4,8 However, none of the articles provided strong evidence on the relationship between the TS of UC and their physical properties such as diameter and weight per unit length. Therefore our objectives were to determine the average tensile strength of human UC and to determine whether there is a relationship between the TS and cord properties such as diameter and weight per unit length. 2. Materials and methods 2.1. Consent, ethical approval and samples
Corresponding author. E-mail addresses: [email protected], [email protected] (S.M.K. Gamage).
https://doi.org/10.1016/j.jflm.2018.03.008 Received 22 September 2017; Received in revised form 6 February 2018; Accepted 5 March 2018 Available online 06 March 2018 1752-928X/ © 2018 Elsevier Ltd and Faculty of Forensic and Legal Medicine. All rights reserved.
Informed written consent from both parents and institutional ethical
Journal of Forensic and Legal Medicine 56 (2018) 48–50
D.M.G. Fernando et al.
approval was obtained prior to sample collection. Umbilical cords were collected from the labor room, Teaching Hospital, Peradeniya, Sri Lanka, from consecutive deliveries. Inclusion criteria were, normal vaginal vertex deliveries between 37 and 40 weeks of period of gestation; deliveries with neonates of birth weights from 2.5 to 3.5 kg and umbilical cords with normal lengths from 40 to 70 cm and with two arteries and one vein.9 Exclusion criteria were, cords of placentas with macroscopic evidence of inflammation and hyper or hypo coiling of cord. Umbilical cords were stored in physiological saline immediately after delivery to preserve the mechanical properties.10 They were either tested immediately or within 12 h after storing in 4 °C. The testing was performed at room temperature (23–32 °C). 2.2. Physical measurements of cords For each cord, the diameters were measured at three sites, i.e. the middle and 2 cm from each end, using a Vernier caliper with an accuracy of 0.1 mm. The sites of measurement of diameter were consistent in all cords. Weights and lengths were measured using an electronic scale and a steel tape with an accuracy of 0.1 g and 1 mm respectively.
Fig. 2. Tensile strength (N) of umbilical cords.
The line graph between the number of cords and tensile strengths (N) roughly resembled a normal distribution (Fig. 2) and the median value was 59 N (6.0 kg). Mean ± SD of TS was 56.3 ± 16.8 N and the average TS was 50.4 N (5.13 kg). The mean diameter of the cords was 7.7 mm. The increase in tensile strength was directly proportional to the diameter (Fig. 3). Average weight per length of the UCs was 6.8 g/cm. No clear relationship was discovered when TS of 98 cords were analyzed with regard to weight per unit length (Fig. 4).
2.3. Testing of tensile strength TS were measured at the Faculty of Engineering, University of Peradeniya, Sri Lanka with Hounsfield Testing Machine which is a computerized Universal Testing Machine with an accuracy of 0.1 N (Fig. 1). One end of the UC was wound around the pulley in the movable arm of machine and the edge of the cord was secured to the machine by tightening it to the arm via screw clips. The other end of the UC was attached to the fixed arm in the same manner and was secured to it by screw clips (Fig. 1). An increasing traction was applied at the rate of 50 mm/min, while a computer continuously generated a stress versus strain graph until the cord broke. The distribution of tensile strengths across the sample, relationship between TS versus umbilical diameter (mm), relationship between TS and weight per unit length of UC were analyzed using GraphPad Prism software.
4. Discussion There are two main occasions in which umbilical cords can break spontaneously. First is during standing and second is while getting up from squatting position.1 However, the force exerted on the cord should exceed the tensile strength of the cord for it to break in an anatomically normal umbilical cord. However, in instances with cord abnormalities, such as velamentous insertion of the cord and deficiencies of Wharton's jelly, easy rupture of the cord is possible.11 Tensile strength of the umbilical cord is the maximum stress the cord can withstand before breaking.4 It is the
3. Results A total of 200 cords were collected adhering to inclusion and exclusion criteria. Of these 51 UC that were too short to be affixed on the machine arms and 27 cords that broke at the pulley were excluded. The remaining 122 cords were tested for TS. The increase in tensile strength was directly proportional to the diameter. When TS of were analyzed with regards to weight per unit length, no clear relationship was discovered.
Fig. 1. Hounsfield testing machine and how the umbilical cords were attached to the fixed and movable arms.
Fig. 3. Tensile Strength (N) versus diameter (mm) of umbilical cords.
49
Journal of Forensic and Legal Medicine 56 (2018) 48–50
D.M.G. Fernando et al.
There were several limitations of the study. Impact of the jerk from baby falling down could not be considered because the Hounsfield machine applied controlled traction on cords and therefore it was not possible to simulate the sudden fall and jerk which actually would occur in precipitate deliveries. Difficulty for manual traction due to the slipperiness of the cord could not be considered as the cord ends were tightly anchored to machine arms. Tensile strengths of the cords could have been correlated with the weights and gestational age of babies, which will be considered in further studies. The height of the baby's fall would be another important factor to be considered. The possibility of the fetus impacting on the floor, without rupture of the umbilical cord, particularly in cases where the mother has a leg height less than the cord length, would be worthwhile considering in future studies. 5. Conclusions On the basis of our study, we would like to advice the forensic pathologists conducting the autopsy, to measure the diameter of the cord, since it correlates to the tensile strength of the cord. Furthermore the tensile strength can be estimated using our findings since it has a directly proportional relationship with the diameter. However the impact of the jerk from baby falling down, difficulty for manual traction from the slipperiness of the cord and maternal anatomical features should be further considered when assessing a cause of precipitous delivery.
Fig. 4. TS (N) versus weight (g) per unit length (10 cm).
highest point of the stress strain curve obtained from a tensile strength test. The average tensile strength of the umbilical cords of the present study was 51.3 N (5.2 kg). This value is higher than the mean tensile strength of the study by Morris et al., which is 49.03 N. However our value is much lower than the mean tensile strengths obtained in the two studies by Pommenich12 and Tantius,1 which are 73.55 N and 79.85 N respectively. Umbilical cords can have a range of tensile strengths due to differences in Wharton's jelly, collagen content and structure of smooth muscle layers of umbilical arteries.5 These physical properties of the umbilical cord may be genetically predetermined or dependent upon the sex, nutritional status and the well being of the fetus.7 Therefore the differences of tensile strength values concluded in the above studies may be attributed to the differences in the genetics, nutritional status and well being of different study population. Furthermore, differences in the experimental setup and the methods used to measure tensile strengths may have caused the observed differences of tensile strengths in the above studies. The diameters of the cords of the present study are directly proportional to the tensile strength. However, the study by Tantius et al. has not found such relationship between cord diameter and tensile strength.1 This may be explained by the sample number. Tantius et al. has used 25 umbilical cords, whereas this study examined 122 cords. Therefore we advocate the measurement of the diameter of the cord, as it can provide a guide to the tensile strength of the cord. However, the weight of the cord is not a reliable index to assess its TS. Out of the 122 cords only 7 (5.7%) had a TS less than 30 N (3.06 kg). The average weight of a newborn baby in Sri Lanka is 3.0 kg.13,14 Therefore, it may be presumed that unless the weight of the baby is greater than the average in Sri Lanka, it is unlikely that the cord will break, due to the baby's weight, except at instances in which there are cord abnormalities, which can affect the tensile strength, such as deficiencies in Wharton's jelly, funisitis and abnormal insertion of cord into the placenta etc. However other factors such as the jerk and the slipperiness of the cord need to be taken into consideration. The mother or some other person can break the cord manually, the slipperiness of the cord being the only difficulty.6 Knight B in 1996 recommends that the length and the severed ends of the cord should be examined during an autopsy on suspicious deaths of newborns.2 Macroscopic and microscopic examination of cords would help to differentiate between a cord which has been torn due to anatomical abnormalities or infection and a cord which has been torn or cut by the culprit.
Funding sources We did not receive any funding for this project. Conflicts of interest Authors declare that they have no conflicts of interests. The work has not been published elsewhere as a full article. Acknowledgements We acknowledge the labor room staff of Teaching Hospital, Peradeniya for the support given for sample recruitment. References 1. Tantius B, Rothschild MA, Valter M, Michael J, Banaschak S. Experimental studies on the tensile properties of human umbilical cords. Forensic Sci Int. 2014 Mar;236:16–21. 2. Knight B, Saukko P. Knight's Forensic Pathology. 4 ed. Florida: Taylor and Francis; CRC press; 2016. 3. de Alwis LBL. Medico legal aspects of Injuries. Colombo, SriLanka: Author; 2007. 4. Ghosh KG, Ghosh SN, Gupta AB. Tensile properties of human umbilical cord. Indian J Med Res. 1984 Apr;79:538–541. 5. Crichton JL. Tensile strength of the umbilical cord. Am J Obstet Gynecol. 1973;115(1):77–80. 6. Morris JF, Hunt AC. Breaking strength of the umbilical cord. J Forensic Sci. 1966 Jan;11(1):43–49. 7. Collins JH, ed. Silent Risk: Issues about the Human Umbilical Cord. 1 ed. USA: Xlibris Corporation; 2002. 8. Itskovitz J, Friedman M, Peretz BA, Brandes JM. Intrauterine rupture of the umbilical cord during delivery. Eur J Obstet Gynecol Reprod Biol. 1980 Jan;10(1):35–40. 9. Balkawade NU, Shinde MA. Study of length of umbilical cord and fetal outcome: a study of 1,000 deliveries. J Obstet Gynaecol India. 2012 Oct;62(5):520–525. 10. Schmidt W. The amniotic fluid compartment: the fetal habitat. Adv Anat Embryol Cell Biol. 1992;1992(127):1–100. 11. Rocha J, Carvalho J, Costa F, Meireles I, do Carmo O. Velamentous cord insertion in a singleton pregnancy: an obscure cause of emergency cesarean—a case report. Case Rep Obs Gynecol. 2012;2012:308206. 12. Pommenich C. Experimentelle Untersuchungen über die Zerreißfestigkeit der menschlichen Nabelschnur: Scheur. 1948; 1948. 13. Kumara DMA, Perera H. Evaluation of Six commonly used formulae for sonographic estimation of fetal weight in Sri lankan population. Sri lanka J Obstet Gynaecol. 2009;31:20–33. 14. Abeyagunawardena IA, Abeynayake A, Anuththara T, et al. Is it appropriate to use WHO Multicentre Growth Reference Study standards to assess the growth parameters of Sri Lankan babies?- A single centre cross sectional study. BMJ Paediatr Open. 2018;2:e000174http://dx.doi.org/10.1136/bmjpo-2017-000174M.
50