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Newborn acid-base status and umbilical cord morphology
Newborn Acid-Base Status and Umbilical Cord Morphology RAMI K. ATALLA, MD, KEITH ABRAMS, PhD, STEPHEN C. BELL, PhD, AND DAVID J. TAYLOR, MD Objective: To assess the relation between umbilical cord morphology and intrapartum fetal status and umbilical cord blood gases at birth. Methods: In a prospective study of 134 consecutive newborns and their umbilical cords, relations were investigated between umbilical cord morphologic characteristics (umbilical cord length, number of vascular coils, coiling index, and vessel length index) and intrapartum fetal heart rate (FHR) decelerations, color of amniotic fluid, operative delivery for suspected fetal acidosis, umbilical vessel blood gases, and acid-base status. Results: Statistically significant linear correlations were found between umbilical venous pH and the umbilical cord length (r 5 0.30; 95% confidence interval [CI] 0.13, 0.46; P < .001), number of vascular coils (r 5 0.27; 95% CI 0.10, 0.43; P 5 .001), coiling index (r 5 0.15; 95% CI 0, 0.33; P 5 .05), and vessel length index (r 5 0.30; 95% CI 0.13, 0.46; P < .001). Statistically significant negative linear correlations were found between the umbilical venous partial pressure of carbon dioxide (PCO2) and cord length (r 5 20.34, 95% CI 20.49, 20.17; P < .001), number of vascular coils (r 5 20.30, 95% CI 20.46, 20.13; P < .001), coiling index (r 5 20.17, 95% CI 20.34, 0; P 5 .03), and vessel length index (r 5 20.34, 95% CI 20.49, 20.17; P < .001). The umbilical artery pH was related to vessel length index and to the number of umbilical vascular coils (r 5 0.17, 95% CI 0.03, 0.36; P 5 .04 and r 5 0.17, 95% CI 0.02, 0.35; P 5 .047, respectively). No relation was found between umbilical cord indices and intrapartum FHR decelerations, meconium staining of the amniotic fluid, or mode of delivery. Placental weight also correlated with umbilical cord length and vessel length index (95% CI 0.15, 0.46; P < .001 and 95% CI 0.05, 0.38; P 5 .01, respectively), but not with the number of umbilical cord coils or the coiling index. Conclusion: Umbilical venous pH and PCO2 and umbilical artery pH are related to umbilical cord morphology. Associated variations in placental morphology or placental blood flow affecting maternal-fetal gas exchange may explain these
From the Departments of Obstetrics and Gynaecology and Epidemiology and Public Health, University of Leicester, Leicester Royal Infirmary, Leicester, United Kingdom.
VOL. 92, NO. 5, NOVEMBER 1998
findings. (Obstet Gynecol 1998;92:865– 8. © 1998 by The American College of Obstetricians and Gynecologists.)
The umbilical vessels are usually coiled around each other in all or part of the length of the cord. Although the mean length of the umbilical cord is 50 – 60 cm, a wide range of lengths (20 –120 cm) has been observed. The number of vascular coils also varies widely. The etiology and importance of these variations are not well understood.1–3 Increased rates of intrapartum fetal heart rate (FHR) decelerations, meconium-stained amniotic fluid, and operative delivery for “fetal distress” have been reported with umbilical cords that have fewer coils.3,4 Strong et al5 introduced the vascular coiling index (number of vascular coils per centimeter) to quantify the degree of umbilical vascular coiling. In their study, operative delivery for “fetal distress” and meconium staining of the amniotic fluid were significantly more common when umbilical cord coiling indices were below the tenth percentile.5 Because FHR changes and passage of meconium have imperfect relations with fetal hypoxia and acidosis, we investigated further the relation between umbilical cord morphology and umbilical pH and blood gases at birth.
Materials and Methods One hundred thirty-four consecutive newborns and their umbilical cords were included in the study over 10 days. We excluded multiple pregnancies, noncephalic presentations, and women with a history of cesarean delivery in a previous pregnancy. Labor was managed independently of the study. The FHR was recorded electronically throughout labor using a cardiotocogram recording monitor (Hewlett Packard 80300A; Hewlett Packard, Boblingen, Germany). The color of the amniotic fluid and the presence or absence of thick, fresh meconium were
0029-7844/98/$19.00 PII S0029-7844(98)00316-0
865
noted. After delivery, the length of the umbilical cord was measured in centimeters from the fetal umbilicus to the chorionic plate. The number of completed vascular coils was noted and the coiling index (the number of vascular coils per centimeter) was calculated. We introduced a “vessel length index” by multiplying the cord length by the number of completed coils to give a total estimate of vessel length. A heparinized sample of blood was drawn from one umbilical artery and from the umbilical vein for blood gas analysis. The blood samples were analyzed with a blood gas analyzer (AVL OMNI 1; AVL, Graz, Austria). Values of pH, partial pressure of oxygen (PO2), and partial pressure of carbon dioxide (PCO2) were measured independently; the base excess was calculated by the gas analyzer from PCO2 values and was not included in the study analysis. The cord was then cut at its placental end, blood was drained, and the placenta was weighed in grams. Cardiotocograms of the entire labor were reviewed by the first author, blinded to the umbilical cord characteristics. Fetal heart rate abnormalities were classified according to the criteria of Kubli et al.6 Severe variable decelerations (FHR below 70 beats per minute for more than 60 seconds) and late decelerations were noted. Instrumental deliveries and cesareans were categorized as operative delivery for suspected fetal acidosis. Fetal acidosis was suspected when the cardiotocogram showed recurrent, severe variable or late FHR decelerations with every contraction for at least 20 minutes of the tracing, with or without a fetal scalp blood pH. Umbilical cord characteristics were analyzed separately, and the assumption of normality was assessed graphically using normal quantile plots. Statistical significance of differences in continuous outcome measures was assessed using two-sample Student t tests. The correlations between them were assessed using Pearson correlation coefficient.
Results The ages of the mothers in the study ranged from 16 to 41 years, with a median age of 28. The median height was 162 cm (range 143–177) and the median maternal weight at booking was 65 kg (range 47–101). The median gestational age was 41 weeks (range 34 – 42). None of the mothers in the study had medical complications that affected the outcome measures. Five infants were born before 37 weeks’ gestation. Analysis with or without their data did not significantly influence the results. Each umbilical cord had three blood vessels. Blood samples for gas analysis were collected successfully from all umbilical veins but from only 79% of the umbilical arteries. Umbilical cord lengths, numbers of
866 Atalla et al
Umbilical Cord and Neonatal Outcome
Table 1. Umbilical Cord Characteristics and Intrapartum Events Intrapartum characteristics Color of amniotic fluid Clear Fresh meconium P Fetal cardiotocogram Reactive Severe variable or late decelerations P Mode of delivery Normal Operative delivery for suspected fetal acidosis P
Cord length (cm)
No. of coils
Coiling index
Vessel length index
59.7 64.3 NS
8.65 8.89 NS
0.15 0.14 NS
545.0 600.5 NS
61.3 59.8
8.62 9.11
0.14 0.15
561.3 563.2
NS
NS
NS
NS
61.4 53.0
8.74 8.83
0.14 0.16
564.5 499.2
NS
NS
NS
NS
NS 5 not significant.
vascular coils, coiling indexes, and vessel length indexes were normally distributed. No statistically significant differences were found between the mean umbilical cord morphologic indices in groups with or without fresh meconium, with or without severe variable or late intrapartum FHR decelerations, or with normal versus operative deliveries for suspected fetal acidosis (Table 1). Statistically significant linear correlations were found between umbilical venous pH and the umbilical cord length (P , .001), number of completed umbilical vascular coils (P 5 .001), coiling index (P 5 .05), and vessel length index (P , .001). Significant negative correlations were also found between umbilical venous PCO2 and cord length (P , .001), number of completed umbilical coils (P , .001), coiling index (P 5 .03), and vessel length index (P , .001) (Table 2). The umbilical artery pH was related to the number of umbilical coils (P 5 .047) and to the vessel length index (P 5 .04), but not to the umbilical cord length (P 5 .06) or the coiling index (P 5 .16). We found no statistically significant correlations between umbilical artery PCO2 and any of the umbilical cord indices (Table 3), or between umbilical cord morphology and umbilical artery or vein PO2. Placental weight correlated with umbilical cord length and vessel length index (P , .001, 95% confidence interval [CI] 0.15, 0.46 and P 5 .01, 95% CI 0.05, 0.38, respectively), but not with the number of umbilical cord coils or the coiling index (P 5 .07, 95% CI 20.04, 0.30 and P 5 .38, 95% CI 20.20, 0.15, respectively).
Discussion The umbilical cord consists of an outer covering of flattened amniotic epithelial cells, containing an interior
Obstetrics & Gynecology
Table 2. Correlations Between Umbilical Cord Characteristics and Umbilical Venous pH and Partial Pressure of Carbon Dioxide Umbilical venous blood gases Umbilical venous pH r ER CI P Umbilical venous PCO2 r ER CI P
Cord length (cm)
No. of coils
Coiling index
Vessel length index
0.30 7.20 1 0.002 3 cord length 0.13, 0.46 ,.001
0.27 7.26 1 0.005 3 number of coils 0.10, 0.43 .001
0.15 7.28 1 0.197 3 coiling index 0, 0.33 .05
0.30 7.27 1 0.0001 3 vessel length index 0.13, 0.46 ,.001
20.34 7.47 2 0.032 3 cord length 20.49, 20.17 ,.001
20.30 6.29 2 0.089 3 number of coils 20.46, 20.13 .001
20.17 6.02 2 3.618 3 coiling index 20.34, 0 .03
20.34 6.17 2 0.001 3 vessel length index 20.49, 20.17 .001
ER 5 equation of the regression line; CI 5 confidence interval; PCO2 5 partial pressure of carbon dioxide.
mass of mesoderm (Wharton’s jelly). Embedded in the latter are two endodermal tubes, the yolk sac and allantoic ducts, and the umbilical vessels. Usually, the embryonic right umbilical vein disappears in the early months of pregnancy, leaving two umbilical arteries and one vein. The vessels in the umbilical cord are rarely straight and usually show a twisted conformation, evident as a right- or left-handed cylindrical helix. The number of twists varies widely. Their cause has been variously ascribed to unequal growth of the vessels or to differential blood flow between the left and right umbilical arteries. Although the etiology is not fully understood, the functional importance has been investigated. The pulse pressure of the two umbilical arteries has been shown to generate a pumping mechanism within the umbilical vein, enhancing venous blood flow.7 This pumping mechanism was shown to be more efficient in highly coiled umbilical cords than in straighter cords. Recently, a direct correlation was found between umbilical cord coiling index and umbilical vein blood flow.8 Meconium staining of the amniotic fluid and instrumental delivery for suspected fetal distress were more common with minimally coiled umbilical cords.3–5 Easy compression of the umbilical
vessels in poorly coiled umbilical cords was suspected to be the reason for these intrapartum findings.3,5 Our study found no correlation between any umbilical cord characteristics and severe variable or late FHR decelerations during labor, development of fresh meconium, or operative delivery for suspected fetal acidosis. In contrast, umbilical vein acid-base status was related to umbilical cord morphologic characteristics. The umbilical vein pH and PCO2 were significantly related to all characteristics of the umbilical cord, in particular umbilical cord length, number of vascular coils, and vessel length index. However, no linear correlation was found between PO2 in the umbilical vessels and umbilical cord indices. These alterations in pH and PCO2 could be explained by imperfect clearance of CO2 because of defects in the placental gas-exchange membranes or placental blood flow. The latter is supported by the more significant correlations found with the umbilical cord indices reflecting the lengths of the umbilical vessels. The lack of relation with PO2 could be explained by the decrease in blood pH associated with a decrease in oxygen affinity of hemoglobin, and a shift of the oxygen-hemoglobin dissociation curve to the right (Bohr effect).
Table 3. Correlations Between Umbilical Cord Characteristics and Umbilical Artery pH and Partial Pressure of Carbon Dioxide Umbilical artery blood gases Umbilical artery pH r CI P Umbilical artery PCO2 r CI P
Cord length (cm)
No. of coils
Coiling index
Vessel length index
0.16 20.04, 0.35 NS
0.17 20.02, 0.35 .047
0.1 20.03, 0.35 NS
0.17 20.03, 0.36 .04
20.06 20.25, 0.14 NS
20.12 20.31, 0.08 NS
20.12 20.30, 0.08 NS
20.11 20.30, 0.08 NS
CI 5 confidence interval; NS 5 not significant; PCO2 5 partial pressure of carbon dioxide.
VOL. 92, NO. 5, NOVEMBER 1998
Atalla et al
Umbilical Cord and Neonatal Outcome
867
Umbilical cord morphology may indirectly reflect placental morphology. Because the umbilical cord and placental vessels have common developmental processes, this seems logical. Supportive evidence for this theory includes our observed relation between umbilical cord length and placental weight. In addition, variations have been detected in the length and coiling of the terminal capillary loops within placentas, and significantly longer and less coiled loops have been found in the small placentas of growth-restricted fetuses.9
7. Reynolds SRM. Mechanisms of placentofetal blood flow. Obstet Gynecol 1978;51:245–9. 8. Degani S, Lewinsky RM, Berger H, Spiegel D. Sonographic estimation of umbilical coiling index and correlation with Doppler flow characteristics. Obstet Gynecol 1995;86:990 –3. 9. Krebs C, Macara L, Leiser R, Bowman A, Greer I, Kingdom J. Intrauterine growth restriction with absent end-diastolic flow velocity in the umbilical artery is associated with maldevelopment of the placental terminal villous tree. Am J Obstet Gynecol 1996; 175:1534 – 42.
Address reprint requests to:
References 1. Edmonds HW. The spiral twist of the normal umbilical cord in twins and singletons. Am J Obstet Gynecol 1954;67:102–20. 2. Malpas P, Symonds EM. Observations on the structure of the human umbilical cord. Surg Gynecol Obstet 1966;123:746 –50. 3. Lacro RV, Jones KL, Benirschke K. The umbilical cord twist: Origin, direction and relevance. Am J Obstet Gynecol 1987;157:833– 8. 4. Strong TH, Elliott JP, Radin TG. Non-coiled umbilical blood vessels: A new marker for the fetus at risk. Obstet Gynecol 1993;81:409 –11. 5. Strong TH, Jarles DL, Vega JS, Feldman DB. The umbilical coiling index. Am J Obstet Gynecol 1994;170:29 –32. 6. Kubli FW, Hon EH, Khazin AF, Takemura H. Observations on heart rate and pH in the human fetus during labor. Am J Obstet Gynecol 1969;104:1190 –206.
868 Atalla et al
Umbilical Cord and Neonatal Outcome
Rami K. Atalla, MD Department of Obstetrics and Gynaecology University of Leicester Clinical Sciences Building Leicester LE2 7LX United Kingdom
Received March 23, 1998. Received in revised form May 27, 1998. Accepted June 19, 1998. Copyright © 1998 by The American College of Obstetricians and Gynecologists. Published by Elsevier Science Inc.
Obstetrics & Gynecology
From the Departments of Obstetrics and Gynaecology and Epidemiology and Public Health, University of Leicester, Leicester Royal Infirmary, Leicester, United Kingdom.
VOL. 92, NO. 5, NOVEMBER 1998
findings. (Obstet Gynecol 1998;92:865– 8. © 1998 by The American College of Obstetricians and Gynecologists.)
The umbilical vessels are usually coiled around each other in all or part of the length of the cord. Although the mean length of the umbilical cord is 50 – 60 cm, a wide range of lengths (20 –120 cm) has been observed. The number of vascular coils also varies widely. The etiology and importance of these variations are not well understood.1–3 Increased rates of intrapartum fetal heart rate (FHR) decelerations, meconium-stained amniotic fluid, and operative delivery for “fetal distress” have been reported with umbilical cords that have fewer coils.3,4 Strong et al5 introduced the vascular coiling index (number of vascular coils per centimeter) to quantify the degree of umbilical vascular coiling. In their study, operative delivery for “fetal distress” and meconium staining of the amniotic fluid were significantly more common when umbilical cord coiling indices were below the tenth percentile.5 Because FHR changes and passage of meconium have imperfect relations with fetal hypoxia and acidosis, we investigated further the relation between umbilical cord morphology and umbilical pH and blood gases at birth.
Materials and Methods One hundred thirty-four consecutive newborns and their umbilical cords were included in the study over 10 days. We excluded multiple pregnancies, noncephalic presentations, and women with a history of cesarean delivery in a previous pregnancy. Labor was managed independently of the study. The FHR was recorded electronically throughout labor using a cardiotocogram recording monitor (Hewlett Packard 80300A; Hewlett Packard, Boblingen, Germany). The color of the amniotic fluid and the presence or absence of thick, fresh meconium were
0029-7844/98/$19.00 PII S0029-7844(98)00316-0
865
noted. After delivery, the length of the umbilical cord was measured in centimeters from the fetal umbilicus to the chorionic plate. The number of completed vascular coils was noted and the coiling index (the number of vascular coils per centimeter) was calculated. We introduced a “vessel length index” by multiplying the cord length by the number of completed coils to give a total estimate of vessel length. A heparinized sample of blood was drawn from one umbilical artery and from the umbilical vein for blood gas analysis. The blood samples were analyzed with a blood gas analyzer (AVL OMNI 1; AVL, Graz, Austria). Values of pH, partial pressure of oxygen (PO2), and partial pressure of carbon dioxide (PCO2) were measured independently; the base excess was calculated by the gas analyzer from PCO2 values and was not included in the study analysis. The cord was then cut at its placental end, blood was drained, and the placenta was weighed in grams. Cardiotocograms of the entire labor were reviewed by the first author, blinded to the umbilical cord characteristics. Fetal heart rate abnormalities were classified according to the criteria of Kubli et al.6 Severe variable decelerations (FHR below 70 beats per minute for more than 60 seconds) and late decelerations were noted. Instrumental deliveries and cesareans were categorized as operative delivery for suspected fetal acidosis. Fetal acidosis was suspected when the cardiotocogram showed recurrent, severe variable or late FHR decelerations with every contraction for at least 20 minutes of the tracing, with or without a fetal scalp blood pH. Umbilical cord characteristics were analyzed separately, and the assumption of normality was assessed graphically using normal quantile plots. Statistical significance of differences in continuous outcome measures was assessed using two-sample Student t tests. The correlations between them were assessed using Pearson correlation coefficient.
Results The ages of the mothers in the study ranged from 16 to 41 years, with a median age of 28. The median height was 162 cm (range 143–177) and the median maternal weight at booking was 65 kg (range 47–101). The median gestational age was 41 weeks (range 34 – 42). None of the mothers in the study had medical complications that affected the outcome measures. Five infants were born before 37 weeks’ gestation. Analysis with or without their data did not significantly influence the results. Each umbilical cord had three blood vessels. Blood samples for gas analysis were collected successfully from all umbilical veins but from only 79% of the umbilical arteries. Umbilical cord lengths, numbers of
866 Atalla et al
Umbilical Cord and Neonatal Outcome
Table 1. Umbilical Cord Characteristics and Intrapartum Events Intrapartum characteristics Color of amniotic fluid Clear Fresh meconium P Fetal cardiotocogram Reactive Severe variable or late decelerations P Mode of delivery Normal Operative delivery for suspected fetal acidosis P
Cord length (cm)
No. of coils
Coiling index
Vessel length index
59.7 64.3 NS
8.65 8.89 NS
0.15 0.14 NS
545.0 600.5 NS
61.3 59.8
8.62 9.11
0.14 0.15
561.3 563.2
NS
NS
NS
NS
61.4 53.0
8.74 8.83
0.14 0.16
564.5 499.2
NS
NS
NS
NS
NS 5 not significant.
vascular coils, coiling indexes, and vessel length indexes were normally distributed. No statistically significant differences were found between the mean umbilical cord morphologic indices in groups with or without fresh meconium, with or without severe variable or late intrapartum FHR decelerations, or with normal versus operative deliveries for suspected fetal acidosis (Table 1). Statistically significant linear correlations were found between umbilical venous pH and the umbilical cord length (P , .001), number of completed umbilical vascular coils (P 5 .001), coiling index (P 5 .05), and vessel length index (P , .001). Significant negative correlations were also found between umbilical venous PCO2 and cord length (P , .001), number of completed umbilical coils (P , .001), coiling index (P 5 .03), and vessel length index (P , .001) (Table 2). The umbilical artery pH was related to the number of umbilical coils (P 5 .047) and to the vessel length index (P 5 .04), but not to the umbilical cord length (P 5 .06) or the coiling index (P 5 .16). We found no statistically significant correlations between umbilical artery PCO2 and any of the umbilical cord indices (Table 3), or between umbilical cord morphology and umbilical artery or vein PO2. Placental weight correlated with umbilical cord length and vessel length index (P , .001, 95% confidence interval [CI] 0.15, 0.46 and P 5 .01, 95% CI 0.05, 0.38, respectively), but not with the number of umbilical cord coils or the coiling index (P 5 .07, 95% CI 20.04, 0.30 and P 5 .38, 95% CI 20.20, 0.15, respectively).
Discussion The umbilical cord consists of an outer covering of flattened amniotic epithelial cells, containing an interior
Obstetrics & Gynecology
Table 2. Correlations Between Umbilical Cord Characteristics and Umbilical Venous pH and Partial Pressure of Carbon Dioxide Umbilical venous blood gases Umbilical venous pH r ER CI P Umbilical venous PCO2 r ER CI P
Cord length (cm)
No. of coils
Coiling index
Vessel length index
0.30 7.20 1 0.002 3 cord length 0.13, 0.46 ,.001
0.27 7.26 1 0.005 3 number of coils 0.10, 0.43 .001
0.15 7.28 1 0.197 3 coiling index 0, 0.33 .05
0.30 7.27 1 0.0001 3 vessel length index 0.13, 0.46 ,.001
20.34 7.47 2 0.032 3 cord length 20.49, 20.17 ,.001
20.30 6.29 2 0.089 3 number of coils 20.46, 20.13 .001
20.17 6.02 2 3.618 3 coiling index 20.34, 0 .03
20.34 6.17 2 0.001 3 vessel length index 20.49, 20.17 .001
ER 5 equation of the regression line; CI 5 confidence interval; PCO2 5 partial pressure of carbon dioxide.
mass of mesoderm (Wharton’s jelly). Embedded in the latter are two endodermal tubes, the yolk sac and allantoic ducts, and the umbilical vessels. Usually, the embryonic right umbilical vein disappears in the early months of pregnancy, leaving two umbilical arteries and one vein. The vessels in the umbilical cord are rarely straight and usually show a twisted conformation, evident as a right- or left-handed cylindrical helix. The number of twists varies widely. Their cause has been variously ascribed to unequal growth of the vessels or to differential blood flow between the left and right umbilical arteries. Although the etiology is not fully understood, the functional importance has been investigated. The pulse pressure of the two umbilical arteries has been shown to generate a pumping mechanism within the umbilical vein, enhancing venous blood flow.7 This pumping mechanism was shown to be more efficient in highly coiled umbilical cords than in straighter cords. Recently, a direct correlation was found between umbilical cord coiling index and umbilical vein blood flow.8 Meconium staining of the amniotic fluid and instrumental delivery for suspected fetal distress were more common with minimally coiled umbilical cords.3–5 Easy compression of the umbilical
vessels in poorly coiled umbilical cords was suspected to be the reason for these intrapartum findings.3,5 Our study found no correlation between any umbilical cord characteristics and severe variable or late FHR decelerations during labor, development of fresh meconium, or operative delivery for suspected fetal acidosis. In contrast, umbilical vein acid-base status was related to umbilical cord morphologic characteristics. The umbilical vein pH and PCO2 were significantly related to all characteristics of the umbilical cord, in particular umbilical cord length, number of vascular coils, and vessel length index. However, no linear correlation was found between PO2 in the umbilical vessels and umbilical cord indices. These alterations in pH and PCO2 could be explained by imperfect clearance of CO2 because of defects in the placental gas-exchange membranes or placental blood flow. The latter is supported by the more significant correlations found with the umbilical cord indices reflecting the lengths of the umbilical vessels. The lack of relation with PO2 could be explained by the decrease in blood pH associated with a decrease in oxygen affinity of hemoglobin, and a shift of the oxygen-hemoglobin dissociation curve to the right (Bohr effect).
Table 3. Correlations Between Umbilical Cord Characteristics and Umbilical Artery pH and Partial Pressure of Carbon Dioxide Umbilical artery blood gases Umbilical artery pH r CI P Umbilical artery PCO2 r CI P
Cord length (cm)
No. of coils
Coiling index
Vessel length index
0.16 20.04, 0.35 NS
0.17 20.02, 0.35 .047
0.1 20.03, 0.35 NS
0.17 20.03, 0.36 .04
20.06 20.25, 0.14 NS
20.12 20.31, 0.08 NS
20.12 20.30, 0.08 NS
20.11 20.30, 0.08 NS
CI 5 confidence interval; NS 5 not significant; PCO2 5 partial pressure of carbon dioxide.
VOL. 92, NO. 5, NOVEMBER 1998
Atalla et al
Umbilical Cord and Neonatal Outcome
867
Umbilical cord morphology may indirectly reflect placental morphology. Because the umbilical cord and placental vessels have common developmental processes, this seems logical. Supportive evidence for this theory includes our observed relation between umbilical cord length and placental weight. In addition, variations have been detected in the length and coiling of the terminal capillary loops within placentas, and significantly longer and less coiled loops have been found in the small placentas of growth-restricted fetuses.9
7. Reynolds SRM. Mechanisms of placentofetal blood flow. Obstet Gynecol 1978;51:245–9. 8. Degani S, Lewinsky RM, Berger H, Spiegel D. Sonographic estimation of umbilical coiling index and correlation with Doppler flow characteristics. Obstet Gynecol 1995;86:990 –3. 9. Krebs C, Macara L, Leiser R, Bowman A, Greer I, Kingdom J. Intrauterine growth restriction with absent end-diastolic flow velocity in the umbilical artery is associated with maldevelopment of the placental terminal villous tree. Am J Obstet Gynecol 1996; 175:1534 – 42.
Address reprint requests to:
References 1. Edmonds HW. The spiral twist of the normal umbilical cord in twins and singletons. Am J Obstet Gynecol 1954;67:102–20. 2. Malpas P, Symonds EM. Observations on the structure of the human umbilical cord. Surg Gynecol Obstet 1966;123:746 –50. 3. Lacro RV, Jones KL, Benirschke K. The umbilical cord twist: Origin, direction and relevance. Am J Obstet Gynecol 1987;157:833– 8. 4. Strong TH, Elliott JP, Radin TG. Non-coiled umbilical blood vessels: A new marker for the fetus at risk. Obstet Gynecol 1993;81:409 –11. 5. Strong TH, Jarles DL, Vega JS, Feldman DB. The umbilical coiling index. Am J Obstet Gynecol 1994;170:29 –32. 6. Kubli FW, Hon EH, Khazin AF, Takemura H. Observations on heart rate and pH in the human fetus during labor. Am J Obstet Gynecol 1969;104:1190 –206.
868 Atalla et al
Umbilical Cord and Neonatal Outcome
Rami K. Atalla, MD Department of Obstetrics and Gynaecology University of Leicester Clinical Sciences Building Leicester LE2 7LX United Kingdom
Received March 23, 1998. Received in revised form May 27, 1998. Accepted June 19, 1998. Copyright © 1998 by The American College of Obstetricians and Gynecologists. Published by Elsevier Science Inc.
Obstetrics & Gynecology