Prenatal buprenorphine exposure: Effects on ... - Wiley Online Library

Acta Obstetricia et Gynecologica. 2008; 87: 1213
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ORIGINAL ARTICLE

Prenatal buprenorphine exposure: Effects on biochemical markers of hypoxia and early neonatal outcome

HANNA KAHILA1, VEDRAN STEFANOVIC1, MIKKO LOUKOVAARA1, ¨ MA ¨ LA ¨ INEN2 & ERJA HALMESMA ¨ KI1 HENRIK ALFTHAN2, ESA HA 1

Department of Obstetrics and Gynecology, 2Department of Clinical Chemistry, Women’s Clinic Laboratory, Helsinki University Central Hospital, Helsinki, Finland

Abstract Objective. To evaluate the possible association between prenatal buprenorphine exposure and compromised early neonatal outcome in view of markers of perinatal hypoxia. Design, setting and sample. The study group consisted of 27 full-term neonates exposed to buprenorphine prenatally and prospectively followed up at a special tertiary outpatient clinic for pregnant drug abusers. Serving as controls were 27 full-term neonates exposed prenatally to illicit substances other than opioids and 38 full-term neonates from uncomplicated pregnancies of healthy parturients. Methods and main outcome measures. Apgar scores, cord pH and base excess were recorded. Cord serum samples were collected at birth for analysis of biochemical markers of fetal hypoxic stress: erythropoietin (EPO; chronic hypoxia), cardiac troponin T (cardiac involvement) and S100 (neural damage). Results. All infants were born in good condition according to Apgar scores and pH of cord blood. No statistically significant differences were found between the three groups in cord serum concentrations of EPO (33.0 median, range: 9.0
476.0 U/L in the buprenorphine-exposed group vs 27.0, range: 8.0
114.0 U/L in substance-abusing controls vs 28.1, range: 11.6
260.0 U/L in healthy controls) or S100 (0.47, range: 0.25
0.91 mg/L vs 0.40, range: 0.12
1.22 mg/L vs 0.47, range: 0.20
2.15 mg/L). No significant differences existed in cardiac TnT levels (0.017, range: 0.010
0.072 U/L vs 0.010, range: 0.010
0.075 U/L vs 0.024, range: 0.010
0.075 U/L). Conclusions. While no significant differences in asphyxia markers were observed between the three groups, a tendency towards higher levels of EPO emerged in the buprenorphine-exposed group.

Key words: Cardiac troponin T, erythropoietin, prenatal buprenorphine, perinatal hypoxia, S100

Introduction Intrauterine exposure to addictive substances is the most significant preventable cause of developmental compromise among children in the developed world. Adverse effects related to substance abuse include poor intrauterine growth (especially as regards head circumference), intrauterine death, prematurity, perinatal asphyxia and sudden infant death (1,2). Subtle changes in brain structure and function have been shown in animal experiments and in humans (3
5), furthermore, the neurobehavioral outcome of infants exposed to drugs in utero is suboptimal (3,5,6). Buprenorphine is a lipophilic partial opioid agonist that is 25
40 times more potent than morphine.

Opioids and the partial agonist buprenorphine are central nervous system (CNS) depressants that can suppress maternal breathing (7,8), decrease umbilical blood flow (9) and produce fetal hypoxia (10), although buprenorphine has a dose-dependent ceiling effect for respiratory depression (7,11). Moreover, the adverse effects of narcotic withdrawal on blood pressure and on oxygen demand of the fetus may have an adverse impact on fetal well-being (12). Therefore, opioid replacement therapy with buprenorphine, or earlier mainly with methadone, has been recommended for co-operative drug addicts during pregnancy (11,13,14). However, the majority of infants born to opioid-dependent mothers will show signs of opioid withdrawal (11).

Correspondence: Hanna Kahila, Department of Obstetrics and Gynecology, Helsinki University Central Hospital, POB 140, FI-00029 HUS, Finland. E-mail: [email protected]

(Received 18 April 2008; accepted 6 September 2008) ISSN 0001-6349 print/ISSN 1600-0412 online # 2008 Informa UK Ltd. (Informa Healthcare, Taylor & Francis AS) DOI: 10.1080/00016340802460297

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Clinically, the neonatal abstinence syndrome (NAS) mimics hypoxic-ischemic encephalopathy. Hypoxic brain injury is a major cause of perinatal death and morbidity and is associated with later neurobehavioral disorders. Hypoxia may affect various fetal tissues, and, as a result, a spectrum of tissue-specific proteins is released into the fetal blood and amniotic fluid (15
19). Hypoxia and ischemia have been recognized as important driving forces of erythropoietin (EPO) expression in the brain. EPO has potent neuroprotective properties and appears to act in a dual way by directly protecting neurones from ischemic damage and by stimulating angiogenesis in the nervous system (20). The fetal liver produces EPO (20), and there is ample evidence that elevated concentrations of EPO in amniotic fluid and cord blood are associated with chronic fetal hypoxia regardless of its origin (15). This has been shown in newborns of pre-eclamptic and diabetic women (21,22), and also in infants exposed to maternal alcohol use (23). Cardiac troponin T (TnT) is expressed in fetal cardiac muscle cells (24), and elevated TnT levels in cord blood are markers of fetal cardiac injury. This is seen in hypoxic fetuses as a result of inadequate blood distribution to spare the fetal heart (25). A high concentration of TnT in cord blood is regarded as an indicator of severe chronic asphyxia, especially in cases with absent and/or reversed flow in the umbilical artery and in fetuses with abnormal venous return as a sign of severe placental insufficiency (25). S100 is a calcium-binding protein. ‘S100’ will be used here as a synonym for the brain-specific S100 subunits [alpha][beta] and [beta][beta], which are strongly and mainly expressed in CNS astroglial cells

(16). The S100 protein content in cord blood is related to the mode of delivery (26). In addition, S100 concentrations in umbilical cord blood and gestational age have been shown to have a correlation (16), and S100 concentrations are increased in amniotic fluid and in cord blood of fetuses with brain damage (16). The aim of this study was to evaluate the early neonatal outcome of newborns exposed to buprenorphine in utero by studying the levels of EPO, cardiac TnT and S100 in cord blood as markers of perinatal hypoxic stress. Materials and methods The study group consisted of 27 pregnant buprenorphine-dependent women prospectively followed up at a special outpatient clinic for pregnant drug abusers, the tertiary antenatal clinic of the Department of Obstetrics and Gynecology, Helsinki University Central Hospital, from a median of 13 weeks3 days (range: 7
27 weeks) of gestation until the end of pregnancy. All subjects smoked tobacco. Serving as controls were 27 pregnant women who abused illicit substances other than opioids, and 38 healthy parturients. There were no preterm or multiple deliveries or other pregnancy complications in these groups. Clinical characteristics of pregnancies and deliveries are shown in Table I. Three subjects were enrolled in a buprenorphine maintenance program before the onset of pregnancy. The rest started buprenorphine replacement therapy during pregnancy at a median of 18 weeks4 days of gestation (range: 6
35 weeks). Ten subjects abused additional street buprenorphine and other substances

Table I. Clinical characteristics of the subjects (n27), substance-abusing controls (n27) and healthy controls (n38). Subjects (n27) Age (years) Hepatitis C antibodies Human Immunodeficiency Virus antibodies Proportion having previous deliveries Smoking 5 cigarettes/day during second trimester Gestational age at delivery (weeks) Vaginal delivery

24.494.2 (range: 18
34)* 21 (78%)* 0

Substance-abusing controls (n 27) 24.696.0 (range 17
42)* 11 (41%)* 1 (4%)

Healthy controls (n 38) 32.195.6 (range: 19
42) 0 0

4 (15%)**

8 (30%)

21 (55%)

27 (100%)*

22 (81%)*

3 (8%)

40.191.6 (range: 35.3
42.2) 24 (89%)

40.193.2 (range 35.0
42.4) 23 (85%)

40.391.0 (range: 37.9
42.1) 38 (100%)

Data are expressed as mean9SD (range) and n (percentage) as appropriate. Comparisons were conducted by analysis of variance, Dunnett’s t-test or Chi-square test. *pB0.0001 compared with healthy controls. **pB0.005 compared with healthy controls.

Prenatal buprenorphine and hypoxia markers

using an Elecsys 2010 analyzer (Roche Diagnostics, Mannheim, Germany). The S100 assay specifically detects the [alpha][beta] and [beta][beta] isoforms of the protein. Our intra-assay CV for serum TnT was B2.4% and total CV B6.3% (tested range: 0.11-2.90 ug/L). For serum S100, the intra-assay and interassay CVs were B3.1% (range: 0.036-4.71 ug/L) and B6.2% (0.22-2.59 ug/L), respectively. The assays were linear up to a concentration of 30 ug/L. Statistical software from SPSS (SPSS Inc., Chicago, IL, USA) was used for data analysis. Comparisons were conducted using analysis of variance, Dunnett’s t-test or the Chi-square test, as appropriate. Spearman correlation coefficients were calculated to examine bivariate relationships. The results are presented as medians (range) unless otherwise stated. A p value B0.05 was considered statistically significant. The Helsinki University Women’s Hospital ethics committee approved the study protocol. All participants gave their informed consent.

according to urine toxicology tests. The median daily buprenorphine doses used are shown in Figure 1. The substance-abusing controls used alcohol (33%), amphetamines (11%), cannabis (33%) or benzodiazepines (4%) based on the results of urine toxicology tests. Twenty-five (93%) of these controls also smoked tobacco. They were followed up starting from a median of 13 gestational weeks (range: 116 to 29 weeks). The pregnancies of the subjects and the substance-abusing controls were followed up every four weeks with fetal biophysical profile and growth, and non-stress tests were performed weekly after 28 gestational weeks. A urine sample for toxicology analysis was requested at every visit. The unexposed pregnancies were followed up according to national guidelines in primary care. Three (8%) of the 38 unexposed controls smoked tobacco, but none abused alcohol or other substances during pregnancy. The clinical data of newborns are shown in Table II. Laboratory analyses of pH, EPO, cardiac TnT and S100 were carried out on cord artery serum samples obtained at delivery, which were then frozen at
188C and later analyzed in the same batch. Serum EPO concentrations were quantified by using an immunochemiluminometric assay in an IMMULITE analyzer (DPC, Los Angeles, CA, USA). The detection limit of the assay is 0.2 U/L. The within-run and total coefficient of variation (CV) was B9% in the concentration range of 7-148 U/L. Serum levels of TnT and S100 were measured by electrochemiluminescence immunoassays (ECLIA)

Results Buprenorphine users were significantly younger and more often nulliparous smokers ( pB0.0001) than the unexposed controls (Table I). The buprenorphine-exposed newborns were approximately 300 g heavier ( pB0.05) than the newborns of the substance-abusing controls (Table II). NAS was diagnosed in 26 (96%) of the buprenorphine-exposed newborns, but in none of the control infants. Because of NAS, the buprenorphine-exposed infants

Buprenorphine dose used (mg) At day of labor

At 36 weeks of gestation

At 30 weeks of gestation

At 24 weeks of gestation

At 18 weeks of gestation

Before 18 weeks of gestation

0

1215

10

20

min -[ lower quartile - median - upper quartile ]- max Figure 1. Daily dose (mg) of buprenorphine used during pregnancy.

30

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H. Kahila et al.

Table II. Characteristics of newborns of subjects (n 27), substance-abusing controls (n27) and healthy controls (n 38). Subjects (n27) Weight of newborn (g) Weight B2 SD for gestational age according to national growth curves Weight of placenta (g) Apgar score at 5 min B7 Umbilical artery pH B7.20 Umbilical artery base excess (BE) B10 Admission to neonatal care unit

Substance-abusing controls (n27)

3,6409303 (range: 1,900
3,900)* 3 (11%)

3,3489455 (range: 2,430
4,070) 1 (4%)

589975# 1 (4%) 9 (33%)#### 2 (7%)####

550982*,## 0 5 (19%)### 0#####

27 (100%)**

5 (19%)

Healthy controls (n38) 3,6119457 (range: 2,550
4,520) 1 (3%) 6389150### 0 9 (24%) 1 (3%) 3 (8%)

Data are expressed as mean9SD (range) and n (percentage), as appropriate. Comparisons were conducted by analysis of variance, Dunnett’s t-test or Chi-square test. *pB0.05 compared with substance-abusing controls. **pB0.0001 compared with both control groups. #One piece of data missing, ##three pieces of data missing, ###six pieces of data missing, ####four pieces of data missing, #####five pieces of data missing.

were admitted more often to the neonatal care unit ( pB0.0001). The newborns in all three groups were born in good condition as defined by Apgar scores, cord pH and base excess values (Table II). No significant differences were present in cord serum EPO levels between the buprenorphineexposed group, substance-abusing controls and unexposed controls, although the overall levels were higher in the buprenorphine-exposed group (Figure 2). In all study groups, a negative correlation ( r0.285) existed between umbilical artery pH and EPO levels, and a positive correlation ( r0.455) between EPO levels and gestational age. No correlation existed between EPO levels and birthweight or between EPO levels and placental weight. Cardiac TnT levels were significantly lower for the substance-abusing controls ( pB0.0001) (Figure 3). There were no correlations between cardiac TnT levels and birthweight, placental weight, pH or gestational age.

S100 levels between study groups did not differ significantly (Figure 4). No correlations were present between S100 levels and birthweight, placental weight, pH or gestational age. In all infants together or in each group separately, no correlations were found between cord serum concentrations of EPO, TnT and S100. Discussion To our knowledge, this is the first study determining both standard clinical parameters of perinatal wellbeing (umbilical pH, Apgar score, admission to NICU) and three biochemical parameters of perinatal hypoxia (EPO, TnT, S100) in newborns exposed prenatally to opioids and/or to buprenorphine. A combination of a low 5-minute Apgar score, need for intubation immediately after delivery and low cord blood pH identifies infants with perinatal asphyxia and those at highest risk of developing

Erythropoietin levels in cord blood

500.0 450.0 400.0

U/L

350.0

Buprenorphine-exposed

300.0 250.0

Controls exposed to substances other than opioids

200.0

"Healthy" controls

150.0 100.0 50.0 0.0

0

5

10

15

20

25

30

Study subjects Figure 2. Erythropoietin levels (U/L) in cord blood in different groups.

35

40

Prenatal buprenorphine and hypoxia markers

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Cardiac troponin-t levels in cord blood

0.0800 0.0700 0.0600

Buprenorphine-exposed

U/L

0.0500 0.0400

Controls exposed to substances other than opioids

0.0300

"Healthy" controls

0.0200 0.0100 0.0000 0

5

10

15

20

25

30

35

40

Study subjects

Figure 3. Cardiac troponin T levels (U/L) in cord blood in different groups.

secondary seizures (17). Recently, several biochemical markers of perinatal asphyxia have been proposed as additional parameters to determine timing and severity of perinatal hypoxia (15,17,18,24); elevated levels of these markers are often seen in newborns with perinatal asphyxia either in utero or intra-partum (19,25). EPO can be used as an indicator of subacute asphyxia because within four hours its levels rise from normal (B50 U/L) to hundreds of units per liter when fetal welfare is compromised (27). We found no signs of asphyxia as defined by high cord blood EPO levels in infants exposed to buprenorphine, although their concentrations showed a tendency towards higher, albeit not statistically significant, levels. Maternal smoking is known to correlate with high cord plasma EPO levels, and in a study of pregnant smokers, cord EPO levels were significantly higher than in non-smokers (28). Most of our buprenorphine users were smokers, which could partly explain the elevated EPO levels in the buprenorphine group, but we cannot definitively state that buprenorphine has an effect on cord EPO levels. We found no correlation between the concentrations of cord serum EPO and TnT or between fetal buprenorphine exposure and cardiac TnT levels.

High TnT concentrations indicate myocardial cell damage (24), but such concentrations were not seen in our subjects. The reason for this could be connected to our co-operative although drug-addicted study population with no major pregnancy or labor complications. There is, however, a case report of a severely opioid- and benzodiazepine-exposed preterm newborn whose drug withdrawal after birth resulted in myocardial ischemia and significantly elevated levels of cardiac enzymes (29). Whether this fetal complication could emerge in association with antenatal drug withdrawal by the mother is not known, as none of our subjects tried to quit buprenorphine use immediately before labor. On the other hand, TnT levels were lower for the substance-abusing controls, although some of the substances abused might be cardiotoxic. The small sample size could have biased this result. The protein S100 may offer an alternative and direct indicator of cell damage in the nervous system when clinical and radiologic assessments are still silent, and it has the additional advantage of providing a quantitative indicator of the extent of brain lesions. It has a good prognostic value in connection with neurodevelopmental outcome after hypoxic-ischemic birth injury (16,19). The infants in this study were

S100 levels in cord blood

2.50

2.00 Buprenorphine-exposed

ug/l

1.50 Controls exposed to substances other than opioids

1.00

"Healthy" controls

0.50

0.00 0

5

10

15

20

25

Study subjects Figure 4. S100 levels (mg/L) in cord blood in different groups.

30

35

40

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born in good condition and had normal S100 levels, although 26/27 of the buprenorphine-exposed subjects developed NAS. Thus, we can only say that despite subsequent NAS, the CNS parameter S100 showed no elevation in these newborns. It is possible, however, that in animal experiments a larger exposure to buprenorphine might result in changes in the concentrations of S100, as was the case in an animal study with ethanol (30). The heterogeneous nature of the substances used by our substance-abusing controls limits the biochemical value of this work, but the substanceabusing control group potentially counteracts the confounding effects of social class and life circumstances on pregnancy outcome. In conclusion, while no significant differences in asphyxia markers were observed between the three groups, a tendency towards higher levels of EPO emerged in the buprenorphine-exposed group.

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Acknowledgements

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Reagents for assay of S100 and TnT were kindly donated by Roche Diagnostics Scandinavia AB (Arsi Itkonen, PhD).

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Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.

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