A case-control study of hypoxic-ischemic encephalopathy in newborn infants at >36 weeks gestation




Objective


The purpose of this study was to determine risk factors that are associated with hypoxic ischemic encephalopathy (HIE).


Study Design


This was a case-control study that included newborn infants with HIE who were admitted to the hospital between January 2001 and December 2008. Two control newborn infants were chosen for each case. Logistic regression and classification and regression tree (CART) analysis that compared control infants and cases with grade 1 HIE and control infants and cases with grades 2 and 3 HIE was performed.


Results


Two hundred thirty-seven cases (newborn infants with grade 1 encephalopathy, 155; newborn infants with grade 2 encephalopathy, 61; newborn infants with grade 3 encephalopathy, 21) and 489 control infants were included. Variables that were associated independently with HIE included higher grade meconium, growth restriction, large head circumference, oligohydramnios, male sex, fetal bradycardia, maternal pyrexia and increased uterine contractility. CART analysis ranked high-grade meconium, oligohydramnios, and the presence of obstetric complications as the most discriminating variables and defined distinct risk groups with HIE rates that ranged from 0–86%.


Conclusion


CART analysis provides information to help identify the time at which intervention in labor may be of benefit.





For Editors’ Commentary, see Contents



Intrapartum asphyxia in mature newborn infants causes 10-15% of cases of cerebral palsy, and its prevention is a major justification for the hospitalization of low-risk mothers who give birth in developed countries. Despite advances in obstetric and neonatal care over the last 4 decades, the rate of cerebral palsy in normally formed newborn infants with a birthweight of >2.5 kg has not declined. In addition, the seizure rate and the neonatal encephalopathy rate in newborn infants with a birthweight of >2.5 kg (which is often a marker of acute intrapartum neonatal brain injury) show no decline.


The objective of this study was to determine risk factors that are associated with the development of hypoxic ischemic encephalopathy (HIE).


Materials and Methods


Patient selection


Inclusion criteria were newborn infants who were born at the Rotunda Maternity Hospital in Dublin from January 2001 to December 2008 at ≥36 weeks 0 days’ gestation and who required admission to the neonatal intensive care unit at ≤24 hours after delivery with evidence of encephalopathy. Newborn infants who were born between January 2001 and July 2005 were identified retrospectively. Newborn infants who were born between July 2005 and December 2008 were identified prospectively.


Grade of encephalopathy was assigned as the highest stage of encephalopathy (Sarnat and Sarnat grading) that had been documented in the clinical notes and/or as noted on serial examination by a member of the research team (B.C.H., M.D.K., or S.M.). Two control newborn infants (the infants who were born before and after each case) were chosen for each case. Exclusion criteria for cases were out-born infants, <36 weeks’ gestation, the presence of a major congenital anomaly, or any primary cause for encephalopathy other than hypoxia-ischemia. Exclusion criteria for control infants were out-born infants, <36 weeks’ gestation, the presence of a major congenital anomaly, or any signs of encephalopathy in the neonatal period. If an infant was excluded as a control, then the infant who was delivered either before or after this infant was chosen.


The obstetrics definitions that were used in data acquisition are outlined in Table 1 .



Table 1

Obstetrics definitions used in data acquisition






































































Variable Definition
Antenatal trauma Significant fall, accident, or abdominal injury in the antenatal period
Late booking Initiation of antenatal care at >24 weeks’ gestation
Pregnancy-induced hypertension Maternal blood pressure ≥140/90 mm Hg on 2 separate occasions >4 hours apart
Preeclampsia New onset hypertension and proteinuria at >20 weeks’ gestation
Proteinuria >0.3 g protein/d in a 24-hour urine collection or, in the absence of a 24-hour urine collection, the presence of 2+ protein on dipstick
Gestational diabetes mellitus Glucose intolerance with onset or first recognition during pregnancy and a normal glucose tolerance test by 6 weeks after delivery
Substantial antepartum hemorrhage Vaginal blood loss equal to or greater than a menstrual period
Nonsubstantial antepartum hemorrhage Vaginal blood loss less than a menstrual period
Fetal bradycardia Decrease in the baseline fetal heart rate <100 beats/min
Late decelerations Transient decrease in fetal heart rate that occurs at or after the peak of a uterine contraction
Fetal tachycardia Increase in baseline fetal heart rate to ≥160 beats/min
Early decelerations Transient decrease in fetal heart rate that coincides with the onset of a uterine contraction
Fetal heart rate variability The beat-to-beat changes in fetal heart rate
Unsatisfactory cardiotocogram The presence of a fetal bradycardia and/or late decelerations and/or fetal tachycardia and/or early decelerations (transient decrease in fetal heart rate that coincides with the onset of a uterine contraction) and/or fetal heart rate variability <5 beats/min
Satisfactory cardiotocogram Baseline rate: 110-160 beats/min; moderate variability; absence of any late or variable decelerations; accelerations that may or may not be present
High-grade meconium Grade 3 (thick or pea soup consistency) meconium or meconium that requires tracheal suction
Maternal pyrexia Temperature ≥38°C measured with a tympanic thermometer
Duration of first stage of labor The time from when the cervix was fully effaced and at least 1-cm dilated (in the presence of regular contractions) up to the time of full dilation
Shoulder dystocia Difficult delivery of the shoulders that required additional obstetric maneuvers to release the shoulders after gentle downward traction failed
Uterine rupture A defect that involves the entire uterine wall that was symptomatic and required surgical intervention
Placental abruption Presence of retroplacental hematoma and clinical symptoms (as assessed by the clinical team at the time of delivery)

Hayes. HIE in newborn infants >36 weeks gestation. Am J Obstet Gynecol 2013 .


Further details on data acquisition are available in the Appendix .


The data were analyzed by logistic regression analysis to identify the variables that were associated independently with HIE and with a classification and regression trees (CART) analysis to help define the distinct clinical groups at higher risk of HIE. CART analysis examines a dataset to find the best variables and associated cutoff points to group the data into those with and without the outcome in question. Splitting stops when the statistical process determines no further discriminating advantage with any of the remaining factors. Two analyses were carried out: 1 analysis compared control infants and cases with grade 1 HIE; 1 analysis compared control infants and cases with grades 2 and 3 HIE. Criteria for inclusion included reaching statistical significance ( P < .25) in the univariate analysis ( Tables 2-4 ) and clinical importance. Factors of clinical importance were defined as factors that have been associated with asphyxia and/or neonatal encephalopathy from previous published studies or deemed important from clinical practice. Logistic regression analysis was used to produce estimates of the odds ratios.



Table 2

Univariate analysis of preconception, antenatal, peripartum, and neonatal factors























































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































Variable Control infants Grade 1 Grade 2 Grade 3 P value a Unadjusted odds ratio 95% CI
n % n % n % n %
Maternal age, y b
≤20 35 7.2 19 12.2 5 8.2 3 14.3 .24 Reference
21-25 93 19.0 39 25.0 12 19.6 4 19.05 0.75 0.407–1.36
26-30 137 28.1 35 22.4 17 27.9 2 9.5 0.51 0.28–0.92
31-37 189 28.7 49 31.4 21 34.4 10 47.6 0.55 0.31–0.96
≥38 34 6.9 14 8.9 6 9.8 2 9.5 0.84 0.40–1.74
Maternal age, y b
<25 108 22.1 51 32.7 14 22.95 7 33.3 .084 0.67 0.47–0.95
≥25 380 77.9 105 67.3 47 77.05 14 66.7
Nationality
Irish/English 355 72.8 118 75.2 36 59.0 12 57.1 < .05 0.84 0.60–1.18
Other 133 27.3 39 24.8 25 41.0 9 42.9
Maternal smoking
0 380 80.5 115 76.2 38 66.7 17 89.5 .17 Reference
1-10/D 58 12.3 25 16.6 12 21.05 2 10.5 1.51 0.97–2.36
11-20/D 31 6.6 10 6.6 6 10.5 0 0 1.16 0.61–2.18
>20/D 3 0.6 1 0.7 1 1.8 0 0 1.5 0.25–9.08
Maternal smoking
No 380 80.5 115 76.2 38 66.7 17 89.5 .19 Reference
Yes 92 19.5 36 23.8 19 33.3 2 10.5 .05 c 1.39 0.95–2.03
Mother consumed alcohol during pregnancy
No 7 1.5 4 2.56 1 1.67 1 4.76 NA NA NA
Yes 72 14.9 31 19.87 10 16.67 5 23.8 NA NA NA
Missing 404 83.6 212 77.5 49 81.67 15 71.4 NA NA NA
Weekly units of alcohol consumed by mother during pregnancy
1-2 42 59.2
3-4 14 19.7 21 67.7 2 50.0 3 60.0 .83
5-7 11 15.5 6 19.4 3 30.0 2 40.0
≥8 4 5.6 2 6.5 0 0 0 0
Regular weekly intake of alcohol (any amount) 92 19.5 2 6.5 2 20.0 0 0
Family history of seizures
No 466 96.9 148 94.9 59 98.3 19 95.0 .33 Reference
Yes 15 3.1 8 5.1 1 1.7 1 5.0 1.38 0.61–3.12
Obstetric history
No 308 64.0 111 71.0 30 51.0 14 67.0 .64 Reference
Yes 173 36.0 45 29.0 29 49.0 7 33.0 < .05 c 0.93 0.67–1.30
Medical/surgical history
No 218 45.7 66 42.3 30 49.2 5 25.0 .33 Reference
Yes 259 54.3 90 57.7 31 50.8 15 75.0 1.14 1.57
Maternal history of respiratory problems
No 442 92.7 145 92.95 59 96.7 17 85.0 Reference
Yes 35 7.3 11 7.05 2 3.3 3 15.0 .98 0.92 0.49–1.70
Maternal history of cardiovascular problems
No 456 95.6 147 94.2 60 98.4 19 95.0 .79 Reference
Yes 21 4.4 9 5.8 1 1.6 1 5.0 1.06 0.50–2.44
Maternal history of gastrointestinal problems
No 445 93.3 142 91.0 56 91.8 17 85.0 .17 Reference
Yes 32 6.7 14 8.97 5 8.2 3 15.0 1.43 0.81–2.52
Maternal history of neurologic problems
No 445 93.3 143 91.7 57 93.4 17 85.0 .31 Reference
Yes 32 6.7 13 8.3 4 6.6 3 15.0 1.29 0.72–2.30
Maternal history of hematologic problems
No 427 89.5 141 90.4 55 90.2 15 75.0 .34 Reference
Yes 50 10.5 15 9.6 6 9.8 5 25.0 1.06 0.64–1.75
Maternal history of muscular problems
No 437 91.6 137 87.8 56 91.8 17 85.0 .29 Reference
Yes 40 8.4 19 12.2 5 8.2 3 15 1.41 0.84–2.36
Maternal history of depression
No 443 92.9 147 94.2 58 95.1 15 75.0 .27 Reference
Yes 34 7.1 9 5.8 3 4.9 5 25.0 < .05 c 1.01 0.55–1.85
Maternal history of infertility
No 464 97.3 147 94.2 60 98.4 17 85.0 .05 Reference
Yes 13 2.7 9 5.8 1 1.6 3 15.0 < .05 c 2.08 0.95–4.57
Maternal history of hypothyroidism
No 469 98.3 154 98.7 61 100.0 20 100.0 .26 Reference
Yes 8 1.7 2 1.3 0 0 0 0 0.50 0.105–2.38
Maternal history of problems (other)
No 369 77.4 118 75.6 46 75.4 12 60.0 .17 Reference
Yes 108 22.6 38 24.4 15 24.6 8 40.0 1.19 0.93–1.71
Primiparity
No 261 54.2 51 32.7 26 43.3 8 38.1 < .001 Reference
Yes 221 45.9 105 67.3 34 56.7 13 61.9 2.08 1.51–2.87
Parity
0 350 72.6 119 76.3 40 66.7 15 71.4 .485 Reference
1 94 19.5 27 17.3 11 18.3 2 9.5 0.86 0.57–1.30
2 32 6.6 8 5.1 8 13.3 0 0 1.01 0.54–1.89
3 6 1.2 2 1.3 1 1.7 4 19.1 2.36 0.78–7.15
Gestational age at time of booking
<12 wk 72 14.9 21 13.5 8 13.3 3 14.3 .06
13-15 wk 223 46.2 73 47.1 23 38.3 6 28.6
16-18 wk 82 16.9 30 19.4 11 18.3 3 14.3
19-23 wk 46 9.5 16 10.3 5 8.3 4 19.0
24-30 wk 26 5.4 8 5.2 5 8.3 3 14.3
31-37 wk 21 4.4 4 2.6 3 5.0 0 0
38-42 wk 10 2.1 1 0.7 4 6.7 1 4.8
Not booked 3 0.62 2 1.3 1 1.7 1 4.8
Gestation age at time of booking ≥24 wk
No 423 87.6 140 90.3 47 78.3 16 76.2 .08 Reference
Yes 60 12.4 15 9.7 13 21.7 5 23.8 1.06 0.66–1.72
Serology
Negative 463 96.9 152 98.1 57 95.0 20 95.2 .66 Reference
Positive 15 3.1 3 1.9 3 5.0 1 4.8 0.95 0.38–2.36
Trauma in pregnancy
No 471 97.7 148 96.1 54 93.1 18 90.0 .01 Reference
Yes 11 2.3 6 3.9 4 6.9 2 10.0 2.35 1.02–5.41
Medications (any) during pregnancy
No 425 90.4 140 91.5 45 81.8 15 83.3 .11 Reference
Yes 45 9.6 13 8.5 10 18.2 3 16.7 1.23 0.74–2.06
Substantial antepartum hemorrhage
No 436 90.6 131 86.2 46 77.97 12 60.0 < .001 Reference
Yes 45 9.4 21 13.8 13 22.03 8 40.0 2.16 1.37–3.41
Growth scans
No 129 26.7 24 15.5 10 16.95 1 5.0 < .001 Reference
Intrauterine growth restriction 8 1.7 6 3.9 0 0 0 0 2.76 0.89–8.49
Normal 345 71.4 125 80.7 48 81.4 19 95.0 2.03 1.34–3.07
Large for dates 1 0.2 0 0 1 1.7 0 0 3.68 0.22–60.42
Abnormal growth
No 345 94.5 125 95.4 48 98.0 19 100.0 .93 Reference
Yes 9 2.5 6 4.6 1 2.0 0 0 1.4 0.52–3.84
Biophysical profile
8/8 313 93.7 118 91.5 45 95.7 19 100.0 .51 Reference
6/8 18 5.4 8 6.2 2 4.3 0 0 0.96 0.43–2.13
Other 3 0.9 3 2.3 0 0 0 0 1.73 0.34–8.68
ARM
No 157 32.5 62 39.5 15 25.9 12 57.1 .18 Reference
Yes 326 67.5 95 60.5 43 74.1 9 42.9 < .05 c 0.78 0.56–1.09
Amniotic fluid volume
Normal 447 92.6 132 84.6 49 84.5 19 90.5 < .05
Oligohydramnios 28 5.8 21 13.5 8 13.8 2 9.5
Polyhydramninos 8 1.7 3 1.9 1 1.7 0 0
Oligohydramnios
No 455 94.2 135 86.5 50 86.2 19 90.5 .01 Reference
Yes 28 5.8 21 13.5 8 13.8 2 9.5 2.48 1.45–4.25
Induction of labor
No 363 75.3 114 73.1 47 79.7 18 85.7 .39 Reference
Yes 119 24.7 42 26.9 12 20.3 3 14.3 0.98 0.68–1.40
Method of induction of labor
No induction 362 76.0 116 74.0 47 79.7 18 85.7 .38 Reference
Prostin, ARM, or syntocinon 32 6.7 13 8.3 3 5.11 1 4.8 1.07 0.57–1.98
Combination of 2 methods 45 9.5 16 10.3 5 8.5 2 9.5 1.03 0.60–1.75
Combination of 3 methods 37 7.8 11 7.1 4 6.8 0 0 0.81 0.44–1.52
Stage 1: duration in hours
0 92 20.5 22 15.6 13 25.0 8 44.4 .08
1-2 106 23.7 26 18.4 8 15.4 1 5.6
3-4 8 1.8 5 3.6 6 11.5 0 0
5-6 95 21.2 17 12.1 4 7.7 1 5.6
7-8 68 15.2 22 15.6 8 15.4 1 5.6
9-12 42 9.4 18 12.7 3 5.8 2 11.1
>12 20 4.5 20 14.2 6 11.5 2 11.1
Not fully dilated 17 3.8 11 7.8 4 7.7 3 16.7
Syntocinon
Stage 1
No 310 66.0 72 48.3 30 54.6 14 73.7 < .05 Reference
Yes 160 34.0 77 51.7 25 45.5 5 26.3 1.75 1.27–2.43
Stage 2
None 307 66.0 65 46.8 25 49.0 15 75.0 .01 Reference
In progress 124 26.7 59 42.5 16 31.4 4 20.0 1.82 1.27–2.61
Stopped 34 7.3 15 10.8 10 19.6 1 5.0 2.23 1.28–3.90
Stage 2
No 307 66.0 65 46.8 25 49.0 15 75.0 < .05 Reference
Yes 158 34.0 74 53.3 26 51.0 5 25.0 1.91 1.37–2.66
Maximum no. of pains per 15 minutes
On partogram
0 44 10.1 8 5.7 10 19.6 3 20.0 < .05
2-4 36 8.2 9 6.4 2 3.9 1 6.7
5-6 172 39.4 35 24.8 15 29.4 4 26.7
7-8 145 33.2 57 40.4 13 25.5 4 26.7
>9 40 9.2 32 22.7 11 21.6 3 20.0
>9
No 397 90.8 109 77.3 40 78.4 12 80.0 < .001 Reference
Yes 40 9.2 32 22.7 11 21.6 3 20.0 2.86 1.80–4.53
>7
No 337 77.1 75 53.2 34 66.7 11 73.3 < .01 Reference
Yes 100 22.9 66 46.8 17 33.3 4 26.7 2.39 1.67–3.41
Analgesia (any)
No 75 15.7 11 7.1 5 8.8 2 9.5 .02 Reference
Yes 404 84.3 143 92.9 52 91.2 19 90.5 2.19 1.27–3.76
Entonox
No 345 72.0 108 70.1 45 78.9 16 76.2 .46 Reference
Yes 134 28.0 46 29.9 12 21.1 5 23.8 0.96 0.68–1.37
Pethidine
No 429 89.6 127 82.5 52 91.2 18 85.7 .33 Reference
Yes 50 10.4 27 17.5 5 8.8 3 14.3 1.53 0.96–2.44
Epidural
No 208 43.4 58 37.7 29 50.9 12 57.1 .37 Reference
Yes 271 56.6 96 62.3 28 49.1 9 42.9 1.01 0.74–1.39
General anesthesia
No 485 99.4 135 86.0 51 83.6 14 66.7 < .001 Reference
Yes 3 0.6 22 14.0 10 16.4 7 33.3 31.74 9.69–103.92
Spinal anesthesia
No 441 92.2 139 93.3 49 86.0 20 95.2 .57 Reference
Yes 37 7.7 10 6.7 8 14 1 4.8 1.09 0.61–1.95
Other analgesia (paracetamol, TENS, fentanyl, remifentanil, solpadeine)
No 470 98.1 144 97.3 55 100.0 21 100.0 .48
Yes 9 1.9 4 2.7 0 0 0 0
Dilation
Fully dilated 431 96.2 130 92.2 48 92.3 15 83.3 .01 Reference
Never fully dilated 17 3.8 11 7.8 4 7.7 3 16.7 2.38 1.20–4.72
Analgesia given
None 75 15.7 11 7.14 5 8.8 2 9.5 < .001 Reference
Epidural only 198 41.3 51 33.1 20 35.1 6 28.6 1.59 0.89–2.84
Epidural plus other analgesia 73 15.2 45 29.2 8 14 3 14.3 3.19 1.71–5.98
Other analgesia, excluding epidural 133 27.8 47 30.5 24 42.1 10 47.6 2.53 1.41–4.54
Mode of delivery
Spontaneous vaginal 291 60.0 45 28.7 15 25.4 7 33.3 < .001 Reference
Ventouse 84 17.4 45 28.7 10 16.95 1 4.7 2.94 1.91–4.53
Forceps 7 1.5 3 1.9 4 6.8 3 14.3 6.32 2.32–17.21
Elective cesarean 41 8.5 1 0.6 1 1.7 0 0 0.215 0.05–0.91
Emergency cesarean 48 9.9 52 33.1 25 42.4 9 42.9 7.92 5.09–12.34
Ventouse and forceps 11 2.3 7 4.5 0 0 0 0 2.81 1.05–7.53
Instrument delivery/emergency cesarean 2 0.4 4 2.6 4 6.8 1 4.8 19.9 4.20–94.29
Other 193 39.8 112 71.3 44 74.6 14 66.7 3.89 2.78–5.46
Spontaneous vaginal/elective cesarean 332 638.6 46 29.3 16 27.1 7 33.3 < .001 Reference
Intervention (any) 152 31.4 111 70.7 46 72.9 14 66.7 5.42 3.84–7.61
Emergency cesarean delivery
No 434 89.7 101 64.3 30 50.9 11 52.4 < .001 Reference
Yes 50 10.3 56 35.7 29 49.2 10 47.6 5.86 3.96–8.67
Maternal pyrexia
No 464 96.3 129 82.3 52 88.1 17 81.0 < .001 Reference
Yes 18 3.7 26 16.8 7 11.9 4 19.0 4.85 2.69–8.73
Maternal antibiotics
No 457 94.6 136 88.9 51 91.1 17 85.0 .01 Reference
Yes 26 5.4 17 11.1 5 8.9 3 15.0 2.16 1.22–3.84
Presentation d
Cephalic 466 96.9 151 96.2 55 94.8 21 100.0 .83 Reference
Breech 10 2.08 1 0.64 2 3.5 0 0 0.619 0.16–2.27
Other 5 1.04 5 3.2 1 1.7 0 0 2.47 0.74–8.21
Presentation d
Cephalic 466 96.9 151 96.2 55 94.8 21 100.0 .84 Reference
Breech/other 15 3.12 6 3.8 3 5.2 0 0 1.23 0.53–2.87
Complications e
None 468 97.1 122 78.7 48 81.4 15 71.4 < .001 Reference
Shoulder dystocia 11 2.3 20 12.9 7 11.9 2 9.5 6.72 3.28–13.73
Other 3 0.6 13 8.4 4 6.8 4 19.05 17.84 5.25–60.53
Complications e
No 468 97.1 122 78.7 48 81.4 15 71.4 < .001 Reference
Yes 14 2.9 33 21.3 11 18.6 6 28.6 9.1 4.91–16.86
Fetal heart rate tracing
Deemed satisfactory 133 31.1 18 11.8 6 10.7 0 0 < .001 Reference
Unsatisfactory 295 68.9 135 88.2 50 89.3 17 100.0 3.76 2.35–6.02
Meconium
Low grade 443 91.9 110 70.06 35 59.3 16 76.2 < .001 Reference
High grade 39 8.1 47 29.9 24 30.7 5 23.8 5.40 3.53–8.28
Resuscitation
No 345 92.7 6 3.9 4 6.6 0 0 < .001 Reference
Yes 27 7.3 147 96.1 57 93.4 21 100.0 287.5 136–605.4
Birthweight percentile for gestational age
≤3rd 31 6.4 17 10.8 10 16.4 0 0 .53 Reference
3rd-97th 422 87.6 132 84.1 45 74.0 19 90.5 < .05 c 0.53 0.307–0.911
≥97th 29 6.0 8 5.1 6 9.8 2 9.5 0.63 0.28–1.40
Occipitofrontal head circumference percentile for gestational age
≤3rd 22 4.7 5 3.3 7 11.9 0 0 .26 Reference
3rd-97th 424 90.6 140 93.3 42 71.2 17 94.4 < .001 c 0.85 0.41–1.76
≥97th 22 4.7 5 3.3 10 16.9 1 5.6 1.33 0.51–3.46
Occipitofrontal head circumference percentile for gestational age ≥97th percentile
No 446 95.3 145 96.7 49 83.1 17 94.4 < .05 Reference
Yes 22 4.7 5 3.3 10 16.95 1 5.6 1.55 0.79–3.00
Birth order
Singleton 486 99.6 153 97.5 60 98.4 21 100.0 .18 Reference
Twin 2 0.4 4 2.6 1 1.6 0 0 5.22 1.00–27.13
Sex
Female 241 49.4 75 47.8 22 36.1 9 42.9 .10 Reference
Male 247 50.6 82 52.2 39 63.9 12 57.1 1.24 0.90–1.69
36-37 wks’ gestation
No 452 94.0 143 91.7 55 91.7 13 65.0 .001 Reference
Yes 29 6.0 13 8.3 5 8.3 7 35.0 1.86 1.06–3.25

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May 13, 2017 | Posted by in GYNECOLOGY | Comments Off on A case-control study of hypoxic-ischemic encephalopathy in newborn infants at >36 weeks gestation

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