Original Article

Mean Arterial Pressure in Extremely Low Birth Weight Concordant and Discordant Twins During the First Day of Life

¹Division of Neonatal-Perinatal Medicine, Pediatrics and Obstetrics, The Ohio State University Medical Center, Columbus, OH, USA

²Maternal-Fetal Medicine, St. Elizabeth's Medical Center of Boston, Boston, MA, USA

³Tufts University School of Medicine, Boston, MA, USA

Correspondence to: Leandro Cordero, MD, Medical Director, Pediatrics Department, Division of Neonatal-Perinatal Medicine, The Ohio State University Medical Center, N118 Doan Hall, 410 W. 10th Avenue, Columbus, OH 43210-1228, USA

Abstract

OBJECTIVE: To determine mean arterial pressure (MAP) values during the first 24 hours for stable concordant and discordant extremely low birth weight (ELBW) twins and to ascertain its association with perinatal factors.

BACKGROUND: In ELBW infants, whether singletons or concordant or discordant twins, hypotension is diagnosed by nonspecific clinical signs together with reference arterial pressure values extrapolated from regression models or from scarce actual observations.

DESIGN: Retrospective cohort study.

METHODS: We studied 26 sets of concordant and 29 sets of discordant twins, one of whom in each set weighed £800 g at birth. Infants with umbilical cord hemoglobin 14 g/dl and who, although mechanically ventilated, had normal acid-base balance, no patent ductus arteriosus, had not received indomethacin, steroids, muscle relaxants, narcotics, were never treated for hypotension, and survived at least 7 days were considered stable. Arterial pressures were determined by oscillometry (OBP) and direct transducer readings using an umbilical line (MAP). All admission and 10 % of the subsequent readings were measured by OBP; the remaining were measured by MAP.

RESULTS: Concordant and discordant twins were similar in demographics, history of chorioamnionitis, preeclampsia, antepartum steroids, cesarean delivery, and neonatal morbidity, but were different in mean birth weight (700 and 789 g), and gestational age (GA) (25 and 27 weeks). Forty-four (82%) of all concordant and 14 (26%) of 58 discordant twins were treated empirically for hypotension. Head ultrasounds were normal or showed Grade I/II in 74% concordant, 81% discordant, and 80% discordant infants with twin-to-twin transfusion syndrome (TTTX). Neonatal mortality was 46%, 45%, and 47%, respectively. There were 14 stable concordant and 22 stable discordant. Their MAPs were different at 1 hour (29 and 34 Torr), 3 hours (29 and 35 Torr), 6 hours (30 and 37 Torr), 12 hours (31 and 36 Torr), 18 hours (33 and 35 Torr), and 24 hours (34 and 36 Torr), respectively. Twenty-six small and 26 large concordant infants had similar MAP from the 1st (27 and 28 Torr) to the 24th hour of life (43 and 43 Torr). Concordant males (often not stable) had lower MAP than concordant females. Seventeen small discordant twins had lower MAP from 1 to 24 hours (28 and 33 Torr) than 17 large discordant twins without TTTX (32 and 38 Torr). Small discordant twins with (donors) and without TTTX had similar trends and MAP values. Large discordant twins with TTTX (recipient) had the highest MAP from birth to 24 hours than any other subgroup of infants and, unlike the others, the MAP trend decreased over time. MAP correlated with GA but not with very low birth weight (£750 g), although with the same GA, those with higher birth weights had higher MAP, and at the same birth weight younger GA twins had lower MAP values.

CONCLUSION: MAP increases from birth to 24 hours in all concordant and discordant twins regardless of condition (stable or unstable), birth weight (large or small) or GA. Recipient TTTX twins had higher MAP throughout but, unlike the other twins, it declined over 24 hours. Small discordant and donor TTTX infants should be considered intrauterine growth restricted and are expected to have MAP commensurable to their GA and not to their birth weight. Journal of Perinatology (2002) 22, 526-534 doi:10.1038/sj.jp.7210785

INTRODUCTION

Recent advances in maternal-fetal medicine and neonatal care make the survival of extremely low birth weight (ELBW) infants likely.¹ Twins still have higher perinatal mortality and morbidity, especially discordant infants whose risks are associated not only with prematurity but also with the discordancy itself.^2,3 Twin-to-twin transfusion syndrome (TTTX) affects a significant number of discordant twins and represents a group with unique fetal growth and cardiovascular compromises.^2,3,4,5,6 Attaining cardiovascular stability often assessed by monitoring arterial pressure is essential in the management of critically ill ELBW infants. It is known that an association exists between systemic hypotension and short and long-term sequelae and mortality^7,8,9,10,11 and that hypotension, which is especially prevalent in the first 24 hours of life, should have timely treatment.^12,13,14 Unfortunately, the decision to treat hypotension is often based on arbitrary blood pressure values with no physiological relevance.^13,15 Furthermore, mean arterial pressure (MAP) reference values for specific populations such as concordant or discordant ELBW twins are not available.

The purpose of this retrospective investigation was to determine MAP for concordant and discordant ELBW twins with and without TTTX syndrome during the first 24 hours of life and to ascertain associations with other perinatal factors.

Study Population

Twenty-six sets of concordant ELBW (all £800 g birth weight) and 29 sets of discordant ELBW twins (at least one infant of each set weighed £800 g) born alive between 1998 and 2001 were evaluated. Comfort care was an exclusion criterion; therefore, in all our cases there was intention to treat. For comparison purposes, 52 concordant and 58 discordant twins were divided into stable and unstable groups. Infants whose umbilical cord hemoglobin was 14 g/dl or greater and who, during the first 24 hours, although mechanically ventilated, had normal acid-base balance, no clinical evidence of a patent ductus arteriosus, had not received indomethacin, steroids, muscle relaxants, narcotics, were never treated for hypotension (packed red blood cells, inotropic agents, colloids), and survived at least 7 days were considered stable. The remaining infants were characterized unstable.

METHODS

Demographic and clinical data were obtained from medical records. This retrospective study was approved by our Institutional Review Board. Gestational age in weeks (GA w) was determined by first trimester ultrasound or by obstetrical dating of the pregnancy and examination of the newborn infant. Discordancy was calculated using the intertwin birth weight difference expressed as a percentage of the larger twin's birth weight.^2,3,16,17 Discordancy equal to or greater than 20% separates concordant from discordant twins. Zygosity was determined prenatally by ultrasound and postnatally by placental examination.¹⁸ TTTX was diagnosed in identical twins by discordance in fetal weight and ultrasonographic documentation of polyhydramnios in one and olygohydramnios in the other.^2,17,19 Significant differences in umbilical cord hemoglobin, which are indicative of acute but not of chronic TTTX, were not used as diagnostic criteria.²

All ELBW infants were treated empirically with ampicillin (100 mg/kg per day IV given in two doses every 12 hours) and gentamicin (5 mg/kg/day IV given every 48 hours) for 2 days if blood cultures were negative. Mechanical ventilation was with a neonatal pressure-limited time-cycled ventilator and, when indicated, with a high-frequency device. Umbilical arterial catheterization was performed for blood gas monitoring and umbilical or central venous catheters were used for long-term parenteral nutrition. During placement of these lines, no more than 3 ml of saline was used for flushing, followed by a continuous infusion of 100 ml/kg per day D5W. Exogenous surfactant (Survanta, Ross Products Division, Abbott Laboratories, Columbus, Ohio) was given at the manufacturer's recommended dosages.

Blood Pressure Measurements

On admission to the NICU, systolic, diastolic, and mean blood pressures were obtained in all limbs by the oscillometric technique (Dinamap, Criticon, Tampa, FL until 1995 and Horizon XL, Mennen Medical, Clarence, NY from 1996 to 2001) using a cuff size 1 (Criticon). Blood pressures were then measured continuously with a disposable pressure transducer (98-4527-RI Abbott Critical Care Systems, Chicago, IL) connected to a single lumen umbilical arterial catheter (Argyle 3.5F catheter) filled with saline or 5% dextrose in water. The catheter was positioned between T-7 and T-10 into the abdominal aorta. This system was calibrated with zero reference at midchest level.

STATISTICAL ANALYSIS

Comparisons between groups and subgroups were made with Student t-tests for interval, and chi-square analysis was used for categorical data. Two hundred and seventeen MAPs obtained by oscillometry (OBP) and 1999 by direct transducer (MAP) were measured in millimeters Hg (Torr). OBP and MAP recorded during short periods of high-frequency ventilation were not included in the analysis. Stepwise multiple linear regressions were made for prediction of MAP at 2, 3, and 4 hours of life by GA, birth weight, percent discordancy in birth weight, history of preterm labor, chorioamnionitis, preeclampsia, antepartum steroids, acute and chronic fetal distress, mode of delivery, Apgar scores, intratracheal epinephrine administration, umbilical cord hemoglobin, and skin temperature on arrival to NICU. Regression analysis was used to determine mean MAP and 80% confidence limits at hourly intervals for concordant, discordant, and TTTX twin groups as to condition (stable), gestational age (£25 and 26 weeks) and birth weight (large and small). Values were reported as mean, standard deviation (SD), range, and median.

RESULTS

During the first 24 hours of life, all 110 infants were on conventional ventilator at rates ranging from 20 to 50 (median 22), peak inflation pressures from 15 to 30 (median 20) cm H₂0, and end expiratory pressures from 4 to 6 cm H₂0 (median 5). For short periods, 4 concordant and 3 discordant twins were also on high-frequency ventilation. During the first 6 hours of life, arterial blood gases in all patients were normal with the exception of moderate metabolic acidosis noted in 3 concordant twins and severe respiratory acidosis noted in 3 large hydropic TTTX who died during the first day. Forty-nine of 52 (94%) concordant and 49 of 58 (84%) discordant twins received exogenous surfactant. Fifty-three of 110 (48%) twins died; of these 26 (49%) did so within the first 3 days of life. All 5 TTTX infants who died did so in the first day of life.

Stepwise multiple linear regression shows that history of preterm labor, chorioamnionitis, preeclampsia, antepartum steroids, acute and chronic fetal distress, mode of delivery, intratracheal epinephrine administration, umbilical cord hemoglobin, and skin temperature on arrival at NICU were not independent predictors of MAP at 2, 3, and 4 hours. Conversely, birth weight, percent discordancy, GA and 1-minute low Apgar scores were predictors of MAP at the same hourly intervals.

Head ultrasounds were obtained during the first day of life in 100 of 110 (91%) of twins but not in 20 infants who died within 48 hours. Normal head ultrasounds were observed in 48% concordant, 59% discordant, and 68% of TTTX infants. Intracranial bleeding (Papille's classification) Grade I/II was noted in 26% concordant, 22% discordant, and 12% TTTX infants. Grade III/IV were found in 26% concordant, 19% discordant, and 20% TTTX infants. Periventricular leukomalacia was observed at 4 weeks of life in 2 discordant small, 1 discordant large and 1 TTTX donor; all of these infants had normal ultrasounds at birth. Fourteen stable concordant infants showed normal (8), Grade I (5), or Grade II (1). Twenty-two stable discordant infants showed normal (18), Grade I (2), and Grade II (2) findings.

Birth weight and gestational age for all the subgroups described above were plotted in a fetal growth nomogram specific for twins.²⁰ Forty-eight of 52 (92%) concordant twins fell between the 50th and 60th percentile whereas the remaining 4 (8%) fell between the 10th and 30th percentile. Among 17 large discordant without TTTX infants, 15 (88%) fell between the 10th and 90th percentile, 1 above the 90th, and 1 below the 10th percentile. Fifteen of 17 (88%) small discordant twins without TTTX fell below the 10th percentile whereas the remaining 2 were between the 10th and 20th percentile. Ten TTTX recipients plotted between the 10th and 70th percentile whereas 2 hydropic infants placed above the 90th percentile. Eleven of 12 TTTX donors plotted below the 10th percentile whereas 1 stayed on the 30th percentile.

CONCORDANT AND DISCORDANT STABLE TWINS

Concordant and discordant twins were similar in demographics, incidence of preterm labor, chorioamnionitis, preeclampsia, history of antenatal steroids, cesarean delivery, and neonatal mortality. They were different in zygocity, incidence of TTTX, mean birth weight (700 and 789 g), and GA (25 and 27 weeks) (Table 1). Twenty-four of 52 (46%) concordant and 29 of 58 (50%) discordant twins died during the neonatal period. Concordant or discordant ELBW twins of £26 wGA had twice the death rate as twins of higher gestational age.

From 1 to 24 hours of life, MAP increased from 29 to 35 Torr for 14 stable concordant and from 34 to 38 Torr for 22 stable discordant twins (Figure 1, A and B). Mean MAP and 10th percentile values for stable concordant infants at 1, 3, 6, 12, 18, and 24 hours were 29 (21), 29 (21), 30 (22), 31 (23), 33 (25), and 35 (26) Torr, respectively. Mean MAP and 10th percentile values from stable discordant infants at 1, 3, 6, 12, 18, and 24 hours were 34 (23), 35 (23), 37 (24), 36 (25), 35 (26), and 38 (26) Torr, respectively.

CONCORDANT TWINS

Comparison between 14 (27%) stable and 38 (73%) unstable concordant twins (Table 2) showed similarities in birth weight, race, low 1-minute Apgar scores, umbilical cord hemoglobin, and neonatal mortality. These groups were different in that 2 of 14 (17%) stable and 21 of 40 (52%) unstable infants were male. Twenty-six of 38 (68%) concordant unstable infants were treated empirically for hypotension. Four (29%) stable and 20 (53%) unstable infants died.

Concordant twin pairs were divided according to birth weight into 26 small (669±71 g) and 26 large (731±84 g) infants. These birth weight differences were statistically significant (p<0.01). Mean MAP and 10th percentile for selected hours are presented in Table 3. Small as well as large infants showed a steady increase of MAP from the first hour (27 and 28 Torr) to 24 hours (32 and 33 Torr). In spite of wide individual variations, no differences in MAP between the two groups were found (Figure 2, A and B). Mean MAP values for 30 concordant £25 wGA and 22 26 wGA infants at 1, 3, 6, 12, 18, and 24 hours were significantly different: 27 and 29, 27 and 30, 28 and 31, 28 and 33, 29 and 35, and 30 and 37 Torr, respectively.

DISCORDANT TWINS

Comparison between 22 stable (38%) and 36 unstable (62%) discordant twins (Table 2) showed similarities in race and sex and significant differences in birth weight, low 1-minute Apgar scores, umbilical cord hemoglobin, incidence of TTTX, and neonatal mortality. Twenty-two of 36 (61%) of unstable discordant infants were treated for hypotension.

Discordant twins were grouped into 34 infants without and 24 with TTTX syndrome. Comparison between these subgroups (Table 4) showed similarities in race, gender, GA, and neonatal mortality. Pairs of discordant twins with and without TTTX were subdivided according to birth weight into large and small infants. On the average, large and small discordant twins with and without TTTX syndrome were similar, except for significantly lower umbilical cord hemoglobin (10 g/dl) among small (donor) TTTX infants. Eleven of 34 (32%) discordant without and 11 of 24 (46%) discordant with TTTX were treated empirically for hypotension.

Mean MAP regression lines and 80th percentile confidence limits for 17 large discordant and 17 small discordant infants without TTTX are presented in Figure 3, A and B. Both groups of infants had a wide range of individual values but still showed steady increases in MAP from 1 to 24 hours. Large discordant infants had higher MAP throughout than small discordant twins (Table 3).

TWIN-TO-TWIN TRANSFUSION (TTTX)

Mean MAP regression lines and 80th percentile confidence limits for 12 (recipient) TTTX and 12 (donor) TTTX infants are presented in Figure 4, A and B. Recipient TTTX started with higher MAP at 1 hour and, unlike any other group of twins studied, presented a steady decline in MAP from 1 hour (47 Torr) to 24 hours (37 Torr). Separate analysis of the 7 TTTX from this group who survived and of the 5 (including three hydropic infants) who died during the first day showed comparable arterial pressure values and a similar pattern of high MAP at 1 hour declining over time. Mean MAP regression lines for donor TTTX infants showed lower MAP at 1 hour (26 Torr) increasing steadily to 24 hours (30 Torr). Donor TTTX infants had lower MAPs than expected for their GA because their values were similar to those of the small concordant twins who were 2 weeks younger in gestation (Table 3). It should also be noted that the average hemoglobin for donor TTTX infants (10 g/dl) was significantly lower when compared with all other groups.

DISCUSSION

Oscillometry is easy to use, measures mean blood pressure as well as heart rate, and eliminates observer variability.²¹ To minimize errors, we used the same cuff size and, because there were no significant differences in OBP values between upper and lower extremities, we averaged all readings.¹⁴ Arterial pressure measurements through a 3.5F umbilical catheter are reproducible^22,23 but could be affected by dampening of the signals. To avoid this, we used MAP and not systolic and diastolic measurement. In our analysis, we felt justified to include 217 oscillometric readings together with 1999 direct pressure determinations, because many investigators^{14,24,25,26,27} have documented good correlation between the two methods.

We selected our study population by birth weight because it is an objective reference point, whereas gestational age, unless obtained by first trimester ultrasound, is of limited value. We focused on the first 24 hours of life because that is when there is a need for diagnosis and treatment for hypotension^12,14 and because, later, many variables such as a patent ductus arteriosus precluded the recognition of a stable population.²⁸ In defining our stable group, like others, we excluded factors that affect blood pressure^8,9,10 but allowed others, such as history of preeclampsia and antenatal steroids, that are now known not to influence MAP in ELBW infants.^11,14

Reference values extrapolated from linear regression models of larger and more mature infants have been found to be inaccurate^23,24 and have not addressed special populations such as ELBW infants and concordant and discordant twins. In the absence of reliable normative data, clinicians have resorted to nonvalidated generalizations, such as assuming that MAP (in Torr) if equated numerically to GA (in weeks) represents the lower limit of normal.^29,30 Poor definition of GA, varying postnatal age at the time of MAP reading, and a wide range of values among infants never treated for hypotension weaken these assumptions.

Obtaining reference values from stable populations, although not always feasible, is important. ELBW infants, especially those of £25 w GA, are seldom stable and have a higher mortality than more mature infants.¹ Thus, it is not surprising that both of our groups of stable infants were skewed toward longer gestations. Stable concordant and stable discordant ELBW twins have lower mortality than their unstable counterparts. They also experience lower morbidity as exemplified by the higher incidence and severity of intracranial hemorrhage among unstable infants.^{8,9,10,11,14,27} Recently, we reported MAP reference values for stable £600-g birth weight infants showing a correlation between GA and MAP and a trend for steady increase in values from 1 hour (30 Torr) to 24 hours (36 Torr).¹⁴ These values are higher than those reported here for concordant stable infants, and this can be explained by the different GA of these groups (27 and 25 w GA, respectively). It is fair to conclude that ELBW concordant twins should have MAP similar to that of singletons of comparable GA.

Discordant stable infants are appropriate-for-gestational-age infants heavier in birth weight and older in GA than stable concordant twins. Thus, higher MAP throughout the study period are to be expected. As a matter of fact, these MAP values were similar to those previously reported for stable infants of comparable birth weight and GA by us¹⁴ and by others.^8,21

In large premature infants, blood pressure has been reported to correlate with birth weight,^21,22,31 a fact supported by the lower MAP noted in concordant when compared with large discordant twins (almost 250 g heavier). This has not been observed in infants whose birth weights were £750 g,^14,26,27 a fact in line with our data that showed no significant MAP differences between small (669±71 g) and large (731±84 g) concordant twins.

By direct observation and by linear regression a strong correlation between GA and blood pressure for full term and premature infants has been noted.^{12,21,22,23,26,30,31} Nuntnarumit et al.²¹ studied 103 infants 23 to 40 wGA and reported lower MAP for those £26 wGA. We corroborated that observation in an earlier investigation¹⁴ as well as in the present study. It would seem that, at the same gestation, larger babies had higher MAP.^21,22,23,30 Our group of large discordant twins had higher MAPs than their small discordant counterparts. It has been noted^14,23,30 that among infants of the same birth weight, those with more advanced GA will have higher MAP. This observation is also validated by the fact that small concordants who had similar birth weight but younger GA had lower MAP than small discordant ELBW infants.

Early in our analysis, it became evident that discordant twins encompassed two different types of patients, those with and those without TTTX syndrome. Severe discordant twins without TTTX syndrome occurred in about 7% of dichorionic and about 20% of monochorionic pregnancies.¹⁷ The most common etiology for this type of discordancy included different genetic potential, unequal sharing of placental mass, and placental insufficiency.^19,32,33 Large discordant infants are usually appropriate for gestation whereas small discordant twins are intrauterine growth restricted. TTTX syndrome, a severe complication of monozygotic twinning, occurred in about 10% of all twin pregnancies as a result of a hemodynamic imbalance caused by placental anastomosis, which leads to discordancy in birth weight.¹⁹

Whether in small or large prematures, MAP increased from birth to 24 hours.^{8,10,14,21,24,29} Our data show that concordant large, concordant small, discordant large, discordant small, and TTTX small infants all followed similar trends. As Heigy et al.²⁷ summarized, "Transitional postnatal changes in cardiac output and vascular resistance are similar in all infants regardless of birth weight. The increase in left ventricular output can be explained by increase in venous return and heart rate and the increase in blood pressure by increased sympathetic stimulation and by a decreased high ventricular systolic and diastolic load. In addition, the carotic baroreceptor, which controls important reflexes in maintaining hemodynamic stability, discharge at similar rates independent of birth weight or gestational age."

Large TTTX (recipients), unlike large discordant twins, start with very high MAP that slowly decline over time. TTTX recipients are known to develop cardiomegaly, right ventricular hypertrophy, decreased right ventricular shortening fraction, triscupid regurgitation, high flow velocities, hydrops, pulsatile venous waveform, and less ventricular involvement.⁶ Whether these or other factors^34,35 explain this reverse trend in MAP needs further study. Because small (donor) twins have hypovolemia, anemia, and growth failure, it is not surprising that they show lower MAP throughout.

Results of this investigation corroborate our earlier report¹⁴ where history of preeclampsia, antenatal steroids, umbilical cord hemoglobin, intratracheal epinephrine administration, and skin temperature on admission did not influence MAP in ELBW infants during the first hours of life. Simultaneously, our observations ratify the association between low Apgar scores and low blood pressures.^9,14,21

In summary, we present MAP reference values for stable concordant and discordant ELBW twins and note that, in spite of a wide individual range of MAP values, there is a relationship with birth weight, gestational age, and postnatal age. Concordant twins behaved like singletons of comparable gestational age. Small discordant twins and donor TTTX are intrauterine growth restricted, whereas their large counterparts (with the exception of hydropic TTTX) are appropriate for gestational age.

Acknowledgements

We acknowledge Larry A. Sachs, PhD, for his assistance with statistical analysis.

References

1 Tyson JE, Younes J, Verter J, Wright LL. Viability, morbidity, and resource use among newborns of 501 - to 800 - g birth weight. JAMA 1996; 276: 1645-51. MEDLINE

2 Sonntag J, Waltz S, Schollmeyer T, Schüppler U, Schröder H, Weisner D. Morbidity and mortality of discordant twins up to 34 weeks of gestational age. Eur J Pediatr 1996; 155: 224-9. MEDLINE

3 Hollier LM, McIntire DD, Leveno KJ. Outcome of twin pregnancies according to intrapair birth weight differences. Obstet Gynecol 1999; 94: 1006-10. MEDLINE

4 Denbow ML, Battin MR, Cowan F, Azzopardi D, Edwards AD, Fisk NM. Neonatal cranial ultrasonographic findings in preterm twins complicated by severe fetofetal transfusion syndrome. Am J Obstet Gynecol 1998; 178: 479-83. MEDLINE

5 Rizzo G, Arduini D, Romanini C. Cardiac and extracardiac flows in discordant twins. Am J Obstet Gynecol 1994; 170: 1321-7. MEDLINE

6 Zosmer N, Bajoria R, Weiner E, Rigby M, Vaughan J, Fisk NM. Clinical and echographic features of in utero cardiac dysfunction in the recipient twin in twin-twin transfusion syndrome. Br Heart J 1994; 72: 74-9. MEDLINE

7 Miall-Allen VM, de Vries LS, Dubowitz LMS, Whitelaw AGL. Blood pressure fluctuation and intraventricular hemorrhage in the preterm infant of less than 31 weeks' gestation. Pediatrics 1989; 83: 657-61. MEDLINE

8 Watkins AMC, West CR, Cooke RWI. Blood pressure and cerebral haemorrhage and ischaemia in very low birthweight infants. Early Hum Dev 1989; 19: 103-10. MEDLINE

9 Bada HS, Korones SB, Perry EH et al. Mean arterial blood pressure changes in premature infants and those at risk for intraventricular hemorrhage. J Pediatr 1990; 117: 607-14. MEDLINE

10 Low JA, Froese AB, Galbraith RS, Smith JT, Sauerbrei EE, Derrick EJ. The association between preterm newborn hypotension and hypoxemia and outcome during the first year. Acta Paediatr 1993; 82: 433-7. MEDLINE

11 Cunningham S, Symon AG, Elton RA, Zhu C, McIntosh N. Intra-arterial blood pressure reference ranges, death and morbidity in very low birthweight infants during the first seven days of life. Early Hum Dev 1999; 56: 151-65. MEDLINE

12 Gill AB, Weindling AM. Echocardiographic assessment of cardiac function in shocked very low birthweight infants. Arch Dis Child 1993; 68: 17-21. MEDLINE

13 Seri I, Evans J. Controversies in the diagnosis and management of hypotension in the newborn infant. Curr Opin Pediatr 2001; 13: 116-23. Article MEDLINE

14 Cordero L, Timan CJ, Waters HH, Sachs LA. Mean arterial pressures during the first 24 hours of life in £600 gram birth weight infants. J Perinatol 2002; 22: 348-53. Article MEDLINE

15 Al-Aweel I, Pursley DM, Rubin LP, Shah B, Weisberger S, Richardson DK. Variations in prevalence of hypotension, hypertension, and vasopressor use in NICUs. J Perinatol 2001; 21: 272-8. Article MEDLINE

16 Fraser D, Picard R, Picard E, Leiberman JR. Birth weight discordance, intrauterine growth retardation and perinatal outcomes in twins. J Reprod Med 1994; 39: 504-8. MEDLINE

17 Victoria A, Mora G, Arias F. Perinatal outcome, placental pathology, and severity of discordance in monochorionic and dichorionic twins. Obstet Gynecol 2001; 97: 310-5. MEDLINE

18 Sherer DM. Adverse perinatal outcome of twin pregnancies according to chorionicity: review of the literature. Am J Perinatol 2001; 18: (1) 23-37. MEDLINE

19 Quintero RA, Morales WJ, Allen MH, Bornick PW, Johnson PK, Kruger M. Staging of twin-twin transfusion syndrome. J Perinatol 1999; 19: 550-5. Article MEDLINE

20 Ananth CV, Vintzileos AM, Shen-Schwarz S, Smulian JC, Lai YL. Standards of birth weight in twin gestations stratified by placental chorionicity. Obstet Gynecol 1998; 91: 917-24. MEDLINE

21 Nuntnarumit P, Yang W, Bada-Ellzey HS. Blood pressure measurements in the newborn. Clin Perinatol 1999; 26: 981-96. MEDLINE

22 Kitterman JA, Phibbs RH, Tooley WH. Aortic blood pressure in normal newborn infants during the first 12 hours of life. Pediatrics 1969; 44: 959-68. MEDLINE

23 Versmold HT, Kitterman JA, Phibbs RH, Gregory GA, Tooley WH. Aortic blood pressure during the first 12 hours of life in infants with birth weight 610 to 4,220 grams. Pediatrics 1981; 67: 607-13. MEDLINE

24 Moscoso P, Goldberg RN, Jamieson J, Bancalari E. Spontaneous elevation in arterial blood pressure during the first hours of life in the very-low-birth-weight infant. J Pediatr 1983; 103: 114-7. MEDLINE

25 Park MK, Menard SM. Accuracy of blood pressure measurement by the Dinamap monitor in infants and children. Pediatrics 1987; 79: 907-14. MEDLINE

26 Spinazzola RM, Harper RG, de Soler M, Lesser M. Blood pressure values in 500- to 750-gram birthweight infants in the first week of life. J Perinatol 1991; XI: 147-51.

27 Hegyi T, Carbone MT, Anwar J et al. Blood pressure ranges in premature infants: I. The first hours of life. J Pediatr 1994; 124: 627-33. MEDLINE

28 Evans N, Moorcraft J. Effect of patency of the ductus arteriosus on blood pressure in very preterm infants. Arch Dis Child 1992; 67: 1169-73. MEDLINE

29 Working Group of the British Association of Perinatal Medicine and the Research Unit of the Royal College of Physicians. Development of audit measurements and guidelines for good practice in the management of neonatal respiratory distress syndrome. Arch Dis Child 1992; 67: 1221-7.

30 Lee J, Rajadurai VS, Tan KW. Blood pressure standards for very low birthweight infants during the first day of life. Arch Dis Child 1999; 81: F168-70.

31 Zubrow AB, Hulman S, Kushner H, Falkner B. Determinants of blood pressure in infants admitted to neonatal intensive care units: a prospective multicenter study. J Perinatol 1995; 15: 470-9. MEDLINE

32 Wenstrom KD, Tessen JA, Zlatnick FJ, Sipes SL. Frequency, distribution, and theoretical mechanisms of hematologic and weight discordance in monochorionic twins. Obstet Gynecol 1992; 80: 257-61. MEDLINE

33 Eberle AM, Levesque D, Vintzileos AM, Egan JF, Tsapanos V, Salafia CM. Placental pathology in discordant twins. Am J Obstet Gynecol 1993; 169: 931-5. MEDLINE

34 Bajoria R, Sooranna SR. Elevated renin-angiotensin levels in the recipient twin of severe twin-twin transfusion syndrome with neonatal hypertension. Placenta 1999; 20: A13, (Abstract).

35 Bajoria R, Ward S, Chatterjee R. Natriuretic peptides in the pathogenesis of cardiac dysfunction in the recipient fetus of twin-twin transfusion syndrome. Am J Obstet Gynecol 2002; 186: 121-7. MEDLINE

Figures

Figure 1 Regression lines and 80% confidence limits: stable concordants MAP=0.237´hours+28.65; stable discordants MAP=0.162´hours+34.31.

Figure 2 Regression lines and 80% confidence limits: small concordant MAP=0.210´hours+26.96; large concordant MAP=0.236´hours+27.76.

Figure 3 Regression lines and 80% confidence limits: small discordant MAP=0.267´hours+28.44; large discordant MAP=0.244´hours+30.97.

Figure 4 TTTX: twin-to-twin transfusion syndrome. Regression lines and 80% confidence limits: small TTTX MAP=0.203´hours+25.49; large TTTX MAP=-0.422´hours+47.04

Tables

Table 1 Study Population

Table 2 Characteristics of Stable and Unstable ELBW twins

Table 3 Mean Arterial Pressure: Mean/10th Percentiles by Diagnosis and Postnatal Age

Table 4 Characteristics of 58 Discordant ELBW Twins

October/November 2002, Volume 22, Number 7, Pages 526-534

Table of contents    Previous  Article  Next    [PDF]