- Email: [email protected]
The impact of prenatal alcohol exposure on frontal cortex development in utero
The impact of prenatal alcohol exposure on frontal cortex development in utero Tara S. Wass, PhD,a Wayne H. Persutte, BS, RDMS,b and John C. Hobbins, MDb Denver, Colo OBJECTIVE: Whether prenatal alcohol exposure was associated with a reduction in the frontal cortex was examined. STUDY DESIGN: Pregnant women (n = 167) received multiple ultrasonographic assessments. During the assessment, brain structures were visualized and measured, including the distance from the posterior margin of the cavum to the calvarium, the distance from the posterior margin of the thalamus to the calvarium, the transcerebellar diameter, and the biparietal diameter. RESULTS: Regression analyses and odds ratios demonstrated that alcohol exposure was associated with a reduction in the frontal cortex, but not other brain structures. Strikingly, the percent of fetuses with a frontal cortex below the 10th percentile increased from 4% for nonexposed fetuses to 23% for heavily exposed fetuses. CONCLUSION: There was a relationship between frontal brain size and maternal alcohol consumption, suggesting that ultrasonography may be a sensitive tool for detecting alcohol-induced changes in the fetal brain. (Am J Obstet Gynecol 2001;185:737-42.)
Key words: Brain development, frontal cortex, prenatal alcohol exposure, ultrasonography
Alcohol use during pregnancy is teratogenic, with effects ranging from neuropsychologic deficits and physical malformations to fetal death.1 The most widely known outcome of drinking during pregnancy is the Fetal Alcohol Syndrome, which is characterized by growth retardation, facial dysmorphology, and central nervous system dysfunction.2 With the incidence of Fetal Alcohol Syndrome estimated at 1 case per 1000 live births, prenatal alcohol exposure is recognized as the leading preventable cause of mental retardation.3 Although warning labels have been attached to alcoholic beverage containers since 1989 and efforts have been directed at educating the public about the effects of drinking during pregnancy, its prevalence is not declining.4 Consequently, drinking during pregnancy remains a significant public health issue. Research suggests that early identification of alcoholexposed children fosters positive outcomes and reduces the likelihood of secondary disabilities.5 Unfortunately, even when women are known to abuse alcohol during From the Department of Psychology, University of Denver,a and the Department of Obstetrics and Gynecology, University of Colorado Health Sciences Center.b Supported by grant #AA05426 from the National Institute of Alcohol Abuse and Alcoholism and funding from the University of Colorado Perinatal Institute. Received for publication October 20, 2000; revised May 10, 2001; accepted May 31, 2001. Reprint requests: Tara S. Wass, PhD, University of Tennessee Child and Family Studies, Knoxville, TN 37996. E-mail: [email protected] Copyright © 2001 by Mosby, Inc. 0002-9378/2001 $35.00 + 0 6/1/117656 doi:10.1067/mob.2001.117656
their pregnancy, alcohol-related anomalies are frequently under-recognized during the neonatal period.6 Additionally, there are no published studies that have documented structural damage to specific brain areas in utero. Such studies could identify markers that could be used by physicians to identify children who should receive comprehensive diagnostic services, long-term follow-up, and intervention services after birth. The current study examined the effects of prenatal alcohol exposure on brain structures in utero. While prenatal alcohol exposure can cause microcephaly, it is relatively rare. In the absence of microcephaly, it is not known whether gross structural damage would be detectable in alcohol-exposed fetuses, although autopsy and magnetic resonance imaging studies suggest that quantifiable structural damage should be evident.7-9 Given the growing body of behavioral evidence suggesting that prenatal alcohol exposure results in deficits typically associated with damage to the frontal cortex,10, 11 and the suggestion that frontal lobe hypoplasia may be a precursor to microcephaly,12 we hypothesized that prenatal alcohol exposure would negatively impact the growth of the frontal cortex. Material and methods We studied 167 pregnant women between 12 and 42 weeks’ gestation. All women reviewed a written description of the study approved by the Institutional Review Board before consenting. Women were recruited from high- and low-risk prenatal clinics at 2 major hospitals in the Denver metropolitan area. Women who reported any alcohol consumption during pregnancy were invited to 737
738 Wass, Persutte, and Hobbins
participate. To ensure sufficient representation of heavy drinkers, women were also recruited from outpatient substance abuse facilities. Additional women who did not drink alcohol were recruited as control participants from the same prenatal clinics. Of the 167 women, 97 consumed little or no alcohol around the time of conception, while 70 consumed moderate to large amounts. Women received 1 to 6 ultrasonographic examinations, depending on their time of study entry and clinical indications. American Registry of Diagnostic Medical Sonographers certified sonographers, blinded to maternal alcohol consumption, performed all examinations with commercially available equipment with electronic calipers using linear dimensions. Four brain measurements were obtained: transcerebellar diameter (TCD), distance from the posterior margin of the thalamus to the inner calvarium (T2C), distance from the posterior margin of the cavum septum pellucidum to the inner surface of the calvarium (frontal lobe [FL]),13 and biparietal diameter (BPD). Interobserver and intraobserver reliability have previously been reported for each of the TCD and BPD measurements,14, 15 but not for FL or T2C. In an independent sample of 10 women with a mean gestational age of 22.8 weeks (range, 17.9 - 28.0 weeks), we found that the average intraobserver reliability was ±1.67 for FL and ±1.78 for T2C. Average interobserver reliability was ±1.83 for FL and ±2.17 for T2C. A measurement of at least 1 of the 3 key measurements (ie, TCD, T2C, FL) was obtained for 155 of the 167 women. None of the key structures could be visualized for the remaining 12 women. All data presented are for the 155 women with at least 1 measurement. Head circumference was also measured. It was highly correlated with BPD (r = .99, P < .001), so its inclusion in the analyses was redundant. Furthermore, no fetus had an extremely small head circumference and 4 of the 5 fetuses with a head circumference 1 or more standard deviations below the mean for their age were in the abstainer or low consumption group. Brain measurements were standardized for gestational age at assessment. The mean and SD of each brain structure were computed for each biweekly interval (0 to 20 biweekly intervals). The z scores were computed by using the biweekly mean and SD. Standard scores were not computed for gestational ages <15 weeks or >36 weeks because of insufficient data (<10 data points). The z scores were averaged across assessments to create an average standardized measure of each structure. Note that the inclusion of the alcohol-exposed fetuses in the construction of the standard scores caused the standard scores to be a conservative estimate of the effect of alcohol exposure. After each ultrasonographic examination, the quantityfrequency-variability method was used to interview women about their alcohol consumption.16 From these interviews, the average ounces of absolute alcohol consumed per day was computed (AA/d). As indicated, the
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time and number of ultrasonographic examinations varied widely across the sample. Consequently, the interval for which alcohol consumption was reported varied widely. We quantified alcohol consumption at conception (weeks 1-4) because data from that time period was available for all participants. At-conception drinking is highly correlated with cross-pregnancy drinking.17 Further, a small sample of the participants was interviewed post partum. The correlation between prenatal reports of drinking at conception and postnatal reports of drinking across the pregnancy was high (r = .67, P < .01), indicating that drinking at conception was a good predictor of overall pregnancy drinking. Women were asked to report the number of cigarettes smoked per day. For all other substances (marijuana, cocaine, methamphetamines, heroin, other illicit drugs), women were asked to report the number of times per week the substance was used. Few women used methamphetamines, heroin, or other illicit drugs; consequently, these data were dichotomously coded to indicate whether the woman used them. The use of cigarettes (n = 10), marijuana (n = 5), cocaine (n = 5), and other drugs (n = 5) could not be confirmed or refuted for some women. Results Data were analyzed by using SPSS 9.0. Mean AA/d was 2.07; however, the distribution was skewed. A categorical variable, reflecting alcohol consumption, was created (Table I). Women consuming <1.00 oz AA/d (<2 drinks/d) were placed into the abstainer/low consumption group. Women consuming 1.00 to 2.99 oz AA/d (25.99 drinks) were classified as moderate drinkers. Finally, women consuming ≥3.00 oz AA/d (≥6 drinks) were considered heavy drinkers. Sixty-seven percent of all women used substances other than alcohol. The likelihood of smoking varied by alcohol group: χ2(2, n = 145) = 12.62, P < .01. Women drinking moderate or heavy amounts of alcohol were more likely to smoke. Among all women who did smoke, the number of cigarettes smoked per day did not vary by alcohol group: F(2, 94) = 2.81, P > .07. The likelihood of using marijuana (χ2[2, n = 150] = 12.81, P < .01]) and cocaine (χ2[2, n = 150] = 10.00, P < .01) also varied by alcohol group. Women consuming heavy amounts of alcohol were more likely than the abstainer/low consumption group to use marijuana (χ2[1, n = 116] = 9.04, P < .01) and cocaine (χ2[1, n = 116] = 9.91, P < .01). Women consuming moderate amounts of alcohol were more likely to use marijuana (χ2[1, n = 122] = 8.70, P < .01), but not cocaine (χ2([1, n = 122] = .61) compared with the abstainer/low consumption group. Among women who used marijuana (F[2, 35] = .31, P > .74) or cocaine (F[2, 26] = .90, P > .42) the number of times it was used per week did not vary by alcohol group. The prevalence of other drug use did not vary by alcohol group.
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Table I. Descriptive statistics for maternal reports of alcohol consumption at conception
AA/d AA/d Abstainer/low Moderate Heavy
n
M
SD
Minimum
Maximum
Skew
155
2.07
5.36
0
58.56
8.12
92 34 29
.23 1.86 8.16
.33 .57 10.39
0 1.01 3.51
.99 2.88 58.56
1.10 .09 4.43
M, Mean; SD, standard deviation; AA/d, ounces of absolute alcohol consumed per day.
Table II. Sample demographic information Alcohol group Abstainer/low
Moderate
Maternal age* (y) 25.80 (5.58) 25.71 (5.05) Gravida† 2.68 (1.69) 2.94 (1.76) Parity‡ .91 (1.17) .79 (.95) Ethnicity (%) African American 4.35 5.90 American Indian 4.35 5.90 Asian 0.00 2.90 Caucasian 40.22 55.90 Hispanic 18.48 17.60 Other/unknown 32.61 11.80
Heavy 26.56 (6.16) 3.21 (2.13) 1.04 (1.23) 0.00 7.10 3.60 57.10 14.30 17.90
*n = 150. †n = 152. ‡n = 151.
Demographic information is presented in Table II. Gravida and parity were not significantly correlated with alcohol group, drug use (Table III), or the standardized brain measurements. Demographic variables were evaluated as predictors of brain structure, but were never significant, and therefore not mentioned later in the article. Descriptive information for the brain measurements is presented in Table IV. Correlations between brain measurements and alcohol and drug consumption are shown in Table V. Univariate correlations indicated that only FL and T2C were related to alcohol consumption. Other drug exposure (ie, cigarettes, marijuana, cocaine, methamphetamines) was not related to any of the brain measurements. These variables were evaluated as predictors of brain structure, but were not significant and therefore not mentioned later in the article. The significant correlations between alcohol consumption, FL, and T2C were followed up with regression analyses. Cigarette exposure and the interaction between cigarette use (no. per day) and alcohol group were also entered into the regression models because there was pervasive use of cigarettes across the sample. The regression analyses examined whether there was a disproportionate effect of alcohol exposure on the frontal cortex, which would suggest the frontal cortex has an increased vulnerability to the teratogenic effects of alcohol. Relationship between FL and alcohol consumption. Alcohol group, TCD, BPD, T2C, the number of cigarettes
smoked per day, and the cigarette by alcohol group interaction were entered into a stepwise regression analysis to determine the best predictors of FL. One multivariate outlier, the fetus of the woman reporting 58.56 oz AA/d at conception, was identified and excluded. T2C, TCD, alcohol group, and the alcohol by cigarette interaction were significant predictors, accounting for 25.4% of the variance in FL (F[4, 111] = 9.47, P < .001 (Table VI). Thus, even after including the size of other brain structures, alcohol consumption still accounted for a significant amount of the variance in FL. Although regression models are useful, assessing their clinical significance can be difficult. To explore the impact of alcohol exposure on the growth of the frontal lobe, we chose the 25th (FL25 ) and 10th (FL10) percentiles as criteria indicative of heightened risk. χ2 analyses indicated that the rates of an FL below the criterion increased significantly with alcohol exposure (Table VII). Previous research18, 19 has suggested that the neurobehavioral effects of prenatal alcohol exposure may be heightened if maternal age is >30 years. To explore this possibility, we examined the moderate and heavily exposed cases, all of whom were exposed to at least 1 oz AA/d at conception, to determine whether the risk of an FL below the 25th or 10th percentiles increased if maternal age was ≥30 years. χ2 analyses indicated that in alcohol-exposed fetuses, maternal age ≥30 years increased the risk of an FL below the 25th percentile, (χ2[1, n = 55] = 5.91; P < .02; odds ratio, 4.5). Maternal age ≥30 years marginally increased the risk of an FL below the 10th percentile, (χ 2[1, n = 55] = 3.18; P < .07; odds ratio, 3.5). These odds ratios demonstrate a substantial interactive risk. While alcohol exposure in isolation was associated with reductions in the size of the frontal cortex, this effect was heightened when maternal age was ≥30 years. Relationship between T2C and alcohol consumption. Alcohol group, FL, TCD, BPD, and the alcohol by cigarette exposure interaction were entered into a stepwise regression analysis to determine the best predictors of T2C (Table VI). BPD and FL entered the model accounting for 15.7% of the variance in T2C: F(2, 114) = 10.62, P < .001. Alcohol exposure and the alcohol by cigarette exposure interaction were not significant predictors. χ2 analyses examined whether the risk of a reduction in the size of the T2C increased with alcohol exposure. The
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Table III. Pearson correlations between maternal demographic variables and drug and alcohol exposure
Maternal age Gravida Parity Cigarette Marijuana Cocaine Alcohol group
Maternal age
Gravida
Parity
Cigarette
Marijuana
Cocaine
Alcohol group
— .406* .405* .071 –.033 .007 .043
— .710* .099 –.030 .118 .117
— .049 –.080 .061 .025
— .180† .171† .309*
— .398* .215*
— .172†
—
*P < .01. †P < .05.
Table IV. Descriptive statistics for average standardized TCD, T2C, FL, and BPD measurements by alcohol group n TCD Abstainer/low Moderate Heavy T2C Abstainer/low Moderate Heavy FL Abstainer/low Moderate Heavy BPD Abstainer/low Moderate Heavy
M*
Table V. Pearson correlations between standardized brain measurements and drug and alcohol exposure TCD
T2C
FL
BPD
— .267* .266* .167† –.062 .079 .115 –.040
— .339* .295* –.093 –.079 .021 –.139†
— .060 .043 –.035 –.014 –.281*
— .049 .073 .047 –.027
SD
86 32 27
.08 .02 .01
.81 .64 .72
86 31 26
.12 –.15 –.12
.82 .81 .75
86 31 26
.17 .04 –.68
.97 1.04 1.15
86 31 26
.06 .05 .00
.76 .84 .65
Sample sizes reflect the number of women per group for whom at least 1 measurement of a given structure could be obtained. TCD, Transcerebellar diameter; T2C, thalamus to inner calvarium; FL, frontal lobe; BPD, biparietal diameter; M, mean; SD, standard deviation. *Z scores are presented. Negative scores indicate that the average standardized length of the structure is shorter than expected.
likelihood of a T2C below the 25th or 10th percentile did not increase as a function of alcohol exposure. Thus, the area between the back of the thalamus and the frontal cortex was not as sensitive to the effects of prenatal alcohol exposure as the frontal cortex alone. The T2C measure may be less sensitive to the effects of alcohol exposure because it included the length of multiple structures, such as the thalamic nuclei, the cerebral peduncles, and the hippocampus, each of which could vary in their sensitivity to the effects of prenatal alcohol exposure. Comment Data from this study represent the first time that ultrasonographically identifiable alcohol-related structural differences have been documented during pregnancy in living human fetuses. Previous studies on alcohol effects have used spontaneously aborted fetuses that were likely to be more severely affected because they were not viable.
TCD T2C FL BPD Cigarettes Marijuana Cocaine Alcohol group
TCD, Transcerebellar diameter; T2C, thalamus to inner calvarium; FL, frontal lobe; BPD, biparietal diameter. *P < .01. †P < .10.
Table VI. Summary of stepwise regression analyses predicting FL and T2C Dependent variable FL
T2C
Variable entered Constant T2C Alcohol group Alcohol group × cigarette TCD Constant BPD FL
B
SE B
β
.636 .404 –.497 .001
.203 .109 .136 .004
— .314 –.376 .246
.267 –.080 .306 .186
.116 .069 .100 .064
.194 — .266 .254
FL, Frontal lobe; T2C, thalamus to inner calvarium; B, unstandardized regression coefficient; SE B, standard error of B; , standardized regression coefficient. TCD, transcerebellar diameter; BPD, biparietal diameter.
Further, imaging studies have only used severely affected children. Most of the children in earlier imaging studies had microcephaly and intelligence scores in the mental retardation range, indicating they were on the severe end of the spectrum. The current sample did not appear to be as severely affected; the alcohol-exposed fetuses were not microcephalic. If microcephaly were present, one would expect a negative relationship between alcohol exposure and the size of the BPD and the TCD, because both are typically highly correlated with gestational age and head circumference. These negative relationships were not found.
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Table VII. Descriptive statistics for the percent of cases with FL below 25th or 10th percentiles Criteria 25th Percentile
10th Percentile
Alcohol group FL25 Abstainer/low Moderate Heavy FL10 Abstainer/low Moderate Heavy
Cases below criteria (%)
Odds ratio*
χ2 χ2(2, n = 143) = 7.52, P < .03
19.77 22.58 46.15
1.18 3.48
4.65 12.90 23.08
3.04 6.15
χ2(2, n = 143) = 8.11, P < .02
FL, Frontal lobe. *Odds ratios were calculated by comparing the moderate and heavy exposure groups individually to the abstainer/low group.
Although the current sample appears to be less severely affected, one could still be concerned that the findings were driven primarily by 1 or more overly influential cases. There was 1 participant who reported an excessively high level of alcohol consumption at conception. It is possible that the woman over-reported her alcohol consumption. However, her fetus was the most severely impacted, as it had the smallest average standardized FL measurement of any fetus (z score = –4.20). Obviously, this case had the potential to be overly influential. However, this case was the multivariate outlier identified and eliminated in the regression analyses and therefore had no influence on the findings. On the basis of the findings, it appears that there was a disproportionate effect of alcohol on the frontal cortex rather than a global effect on the brain. Surprisingly, 46% of heavily exposed fetuses had a frontal cortex length below the 25th percentile. In contrast, only 20% of nonexposed fetuses were below this criterion. When the 10th percentile was used as a criterion, the results were just as striking. The finding that reductions in specific brain structures, but not global brain size, were associated with prenatal alcohol exposure was not entirely surprising. Microcephaly is observed only in the most severely affected children. It would be surprising if there were no effect on the brain except when microcephaly occurs. Recently, Persutte12 argued that a shortening of the frontal cortex during gestation might be a precursor to microcephaly. Reductions in the frontal cortex observed in this sample were consistent with neuropsychologic10 and anecdotal reports20 of executive functioning deficits in alcoholexposed children. Executive functioning problems include difficulties updating and manipulating information in working memory, inhibiting information and actions, and sustaining attention.21 Executive functioning problems can disrupt the child’s functioning within family, school, and peer settings. These types of deficits are present in a variety of developmental disorders, such as attention deficit-hyperactivity disorder, autism, and early treated phenylketonuria.21-23 Further, executive functioning deficits can cause significant difficulties even when the child has an IQ score within the normal range.
While alcohol exposure was predictive of the length of the frontal cortex, a relatively small amount of variance was accounted for in the regression model. Although one would not expect to see a large correlation between exposure and the size of brain structures, it is possible that the relationship was limited by the measures of alcohol consumption used. We reported alcohol consumption at conception because consumption across the duration of the pregnancy could not be quantified for many participants. Alcohol consumption limited to the at-conception period is unlikely to cause a reduction in size specific to the frontal cortex because individual brain structures are not differentiated at that time. Although drinking at conception is correlated with drinking during the pregnancy, solely using at-conception drinking limits our ability to examine the effects of prenatal alcohol exposure at different times throughout the pregnancy. For example, it is not known how many of the women continued to consume alcohol through the third trimester brain growth spurt. It is likely that consumption during the third trimester would result in the most profound reductions in brain size. In contrast, if a woman consumed alcohol early in pregnancy, but abstained from drinking later in pregnancy, it is possible that the brain could compensate. Several studies provide indirect support for this hypothesis by showing that the magnitude of neurologic and neurobehavioral deficits is reduced if women do not drink during the third trimester.24, 25 Further studies need to examine whether the fetal brain can compensate for early exposure if maternal consumption ceases during pregnancy. If it can be demonstrated that both alcohol-induced structural changes and neuronal compensation after the cessation of drinking can be detected, ultrasonography could become a powerful primary intervention tool for physicians to concretely demonstrate the effects of pregnancy drinking and to encourage women who drink during pregnancy to seek treatment. The current study demonstrated that ultrasonography can be used to document in utero reductions in specific brain structures associated with alcohol exposure. It is not known whether these findings will be predictive of later
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development. We do not know whether the alcohol-related changes in frontal lobe development will translate into meaningful differences in neurobehavioral functioning. If it can be demonstrated that alcohol-related changes in brain structure are predictive of postnatal development of the child, ultrasonography could become a powerful tool not only in the prenatal diagnosis of teratogeninduced disorders, but also in examining the link between brain development and behavior during the early formative years. We thank Dr Marshall Haith, Dr Sandra Jacobson, and Dr Joseph Jacobson who contributed much toward the successful completion of this research.
REFERENCES
1. Mattson SN, Riley EP. A review of the neurobehavioral deficits in children with fetal alcohol syndrome or prenatal exposure to alcohol. Alcohol Clin Exp Res 1998;22:279-94. 2. Institute of Medicine (US). Fetal alcohol syndrome: diagnosis, epidemiology, prevention, and treatment. Washington, DC: National Academy Press; 1996. 3. Abel EL. An update on incidence of FAS: FAS is not an equal opportunity birth defect. Neurotoxicol Teratol 1995;17:437-43. 4. Ebrahim SH, Luman ET, Floyd RL, Murphy CC, Bennett EM, Boyle CA. Alcohol consumption by pregnant women in the United States during 1988-1995. Obstet Gynecol 1998;92:187-92. 5. Streissguth AP, Barr HM, Kogan J, Bookstein FL. Understanding the occurrence of secondary disabilities in clients with fetal alcohol syndrome and fetal alcohol effects. Seattle: University of Washington Publication Services. 1996. 6. Stoler JM, Holmes LB. Under-recognition of prenatal alcohol effects in infants of known alcohol abusing women. J Pediatr 1999;135:430-6. 7. Roebuck TM, Mattson SN, Riley EP. A review of the neuroanatomical findings in children with fetal alcohol syndrome or prenatal exposure to alcohol. Alcohol Clin Exp Res 1998;22:339-44. 8. Clarren SK, Alvord EC Jr, Sumi SM, Streissguth AP, Smith DW. Brain malformations related to prenatal exposure to ethanol. J Pediatr 1978;92:64-7. 9. Wisniewski K, Dambska M, Sher JH, Qazi Q. A clinical neuropathological study of the fetal alcohol syndrome. Neuropediatr 1983;14:197-201.
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10. Mattson SN, Goodman AM, Caine C, Delis DC, Riley EP. Executive functioning in children with heavy prenatal alcohol exposure. Alcohol Clin Exp Res 1999;23:1808-15. 11. Olson HC, Feldman JJ, Streissguth AP, Sampson PD, Bookstein FL. Neuropsychological deficits in adolescents with fetal alcohol syndrome: clinical findings. Alcohol Clin Exp Res 1998;22:19982012. 12. Persutte WH. Microcephaly—no small deal. Ultrasound Obstet Gynecol 1998;11:317-8. 13. Persutte WH, Coury A, Hobbins JC. Correlation of fetal frontal lobe and transcerebellar diameter measurements: the utility of a new prenatal sonographic technique. Ultrasound Obstetr Gynecol 1997;10:94-7. 14. Kiserud T, Saito T, Ozaki T, Rasmussen S, Hanson MA. Validations of diameter measurements by ultrasound: intraobserver and interobserver variations assessed in vitro and in fetal sheep. Ultrasound Obstet Gynecol 1999;13:52-7. 15. Harstad TW, Buschang PH, Little BB, Santos-Ramos R, Twickler D, Brown CE. Ultrasound anthropometric reliability. J Clin Ultrasound 1994;22:531-4. 16. Streissguth AP, Barr HM, Sampson PD, Darby BL, Martin DC. IQ at age 4 in relation to maternal alcohol use and smoking during pregnancy. Dev Psychol 1989;25:3-11. 17. Jacobson SW, Jacobson JL, Sokol RJ, Martier SS, Ager JW, Kaplan MG. Maternal recall of alcohol, cocaine, and marijuana use during pregnancy. Neurotoxicol Teratol 1991;13:535-40. 18. Jacobson JL, Jacobson SW, Sokol RJ, Ager JW Jr. Relation of maternal age and pattern of pregnancy drinking to functionally significant cognitive deficit in infancy. Alcohol Clin Exp Res 1998;22:345-51. 19. Jacobson JL, Jacobson SW, Sokol RJ. Increased vulnerability to alcohol-related birth defects in the offspring of mothers over 30. Alcohol Clin Exp Res 1996;20:359-63. 20. Streissguth AP, Kanter J. The challenge of fetal alcohol syndrome: overcoming secondary disabilities. Seattle: University of Washington Press; 1997. 21. Pennington BF, Ozonoff S. Executive functions and developmental psychopathology. J Child Psychol Psychiatry 1996;37:51-87. 22. Welsh MC, Pennington BF, Ozonoff S, Rouse B, McCabe ERB. Neuropsychology of early-treated phenylketonuria: specific executive functioning deficits. Child Dev 1990;61:1697-1713. 23. Welsh MC, Pennington BF. Assessing frontal lobe functioning in children: views from developmental psychology. Dev Neuropsychol 1988;4:199-230. 24. Coles CD, Smith I, Fernhoff PM, Falek A. Neonatal neurobehavioral characteristics as correlates of maternal alcohol use during gestation. Alcohol Clin Exp Res 1985;9:454-60. 25. Coles CD, Brown RT, Smith IE, Platzman KA, Erickson S, Falek A. Effects of prenatal alcohol exposure at school age. I. Physical and cognitive development. Neurotoxicol Teratol 1991;13:357-67.
Key words: Brain development, frontal cortex, prenatal alcohol exposure, ultrasonography
Alcohol use during pregnancy is teratogenic, with effects ranging from neuropsychologic deficits and physical malformations to fetal death.1 The most widely known outcome of drinking during pregnancy is the Fetal Alcohol Syndrome, which is characterized by growth retardation, facial dysmorphology, and central nervous system dysfunction.2 With the incidence of Fetal Alcohol Syndrome estimated at 1 case per 1000 live births, prenatal alcohol exposure is recognized as the leading preventable cause of mental retardation.3 Although warning labels have been attached to alcoholic beverage containers since 1989 and efforts have been directed at educating the public about the effects of drinking during pregnancy, its prevalence is not declining.4 Consequently, drinking during pregnancy remains a significant public health issue. Research suggests that early identification of alcoholexposed children fosters positive outcomes and reduces the likelihood of secondary disabilities.5 Unfortunately, even when women are known to abuse alcohol during From the Department of Psychology, University of Denver,a and the Department of Obstetrics and Gynecology, University of Colorado Health Sciences Center.b Supported by grant #AA05426 from the National Institute of Alcohol Abuse and Alcoholism and funding from the University of Colorado Perinatal Institute. Received for publication October 20, 2000; revised May 10, 2001; accepted May 31, 2001. Reprint requests: Tara S. Wass, PhD, University of Tennessee Child and Family Studies, Knoxville, TN 37996. E-mail: [email protected] Copyright © 2001 by Mosby, Inc. 0002-9378/2001 $35.00 + 0 6/1/117656 doi:10.1067/mob.2001.117656
their pregnancy, alcohol-related anomalies are frequently under-recognized during the neonatal period.6 Additionally, there are no published studies that have documented structural damage to specific brain areas in utero. Such studies could identify markers that could be used by physicians to identify children who should receive comprehensive diagnostic services, long-term follow-up, and intervention services after birth. The current study examined the effects of prenatal alcohol exposure on brain structures in utero. While prenatal alcohol exposure can cause microcephaly, it is relatively rare. In the absence of microcephaly, it is not known whether gross structural damage would be detectable in alcohol-exposed fetuses, although autopsy and magnetic resonance imaging studies suggest that quantifiable structural damage should be evident.7-9 Given the growing body of behavioral evidence suggesting that prenatal alcohol exposure results in deficits typically associated with damage to the frontal cortex,10, 11 and the suggestion that frontal lobe hypoplasia may be a precursor to microcephaly,12 we hypothesized that prenatal alcohol exposure would negatively impact the growth of the frontal cortex. Material and methods We studied 167 pregnant women between 12 and 42 weeks’ gestation. All women reviewed a written description of the study approved by the Institutional Review Board before consenting. Women were recruited from high- and low-risk prenatal clinics at 2 major hospitals in the Denver metropolitan area. Women who reported any alcohol consumption during pregnancy were invited to 737
738 Wass, Persutte, and Hobbins
participate. To ensure sufficient representation of heavy drinkers, women were also recruited from outpatient substance abuse facilities. Additional women who did not drink alcohol were recruited as control participants from the same prenatal clinics. Of the 167 women, 97 consumed little or no alcohol around the time of conception, while 70 consumed moderate to large amounts. Women received 1 to 6 ultrasonographic examinations, depending on their time of study entry and clinical indications. American Registry of Diagnostic Medical Sonographers certified sonographers, blinded to maternal alcohol consumption, performed all examinations with commercially available equipment with electronic calipers using linear dimensions. Four brain measurements were obtained: transcerebellar diameter (TCD), distance from the posterior margin of the thalamus to the inner calvarium (T2C), distance from the posterior margin of the cavum septum pellucidum to the inner surface of the calvarium (frontal lobe [FL]),13 and biparietal diameter (BPD). Interobserver and intraobserver reliability have previously been reported for each of the TCD and BPD measurements,14, 15 but not for FL or T2C. In an independent sample of 10 women with a mean gestational age of 22.8 weeks (range, 17.9 - 28.0 weeks), we found that the average intraobserver reliability was ±1.67 for FL and ±1.78 for T2C. Average interobserver reliability was ±1.83 for FL and ±2.17 for T2C. A measurement of at least 1 of the 3 key measurements (ie, TCD, T2C, FL) was obtained for 155 of the 167 women. None of the key structures could be visualized for the remaining 12 women. All data presented are for the 155 women with at least 1 measurement. Head circumference was also measured. It was highly correlated with BPD (r = .99, P < .001), so its inclusion in the analyses was redundant. Furthermore, no fetus had an extremely small head circumference and 4 of the 5 fetuses with a head circumference 1 or more standard deviations below the mean for their age were in the abstainer or low consumption group. Brain measurements were standardized for gestational age at assessment. The mean and SD of each brain structure were computed for each biweekly interval (0 to 20 biweekly intervals). The z scores were computed by using the biweekly mean and SD. Standard scores were not computed for gestational ages <15 weeks or >36 weeks because of insufficient data (<10 data points). The z scores were averaged across assessments to create an average standardized measure of each structure. Note that the inclusion of the alcohol-exposed fetuses in the construction of the standard scores caused the standard scores to be a conservative estimate of the effect of alcohol exposure. After each ultrasonographic examination, the quantityfrequency-variability method was used to interview women about their alcohol consumption.16 From these interviews, the average ounces of absolute alcohol consumed per day was computed (AA/d). As indicated, the
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time and number of ultrasonographic examinations varied widely across the sample. Consequently, the interval for which alcohol consumption was reported varied widely. We quantified alcohol consumption at conception (weeks 1-4) because data from that time period was available for all participants. At-conception drinking is highly correlated with cross-pregnancy drinking.17 Further, a small sample of the participants was interviewed post partum. The correlation between prenatal reports of drinking at conception and postnatal reports of drinking across the pregnancy was high (r = .67, P < .01), indicating that drinking at conception was a good predictor of overall pregnancy drinking. Women were asked to report the number of cigarettes smoked per day. For all other substances (marijuana, cocaine, methamphetamines, heroin, other illicit drugs), women were asked to report the number of times per week the substance was used. Few women used methamphetamines, heroin, or other illicit drugs; consequently, these data were dichotomously coded to indicate whether the woman used them. The use of cigarettes (n = 10), marijuana (n = 5), cocaine (n = 5), and other drugs (n = 5) could not be confirmed or refuted for some women. Results Data were analyzed by using SPSS 9.0. Mean AA/d was 2.07; however, the distribution was skewed. A categorical variable, reflecting alcohol consumption, was created (Table I). Women consuming <1.00 oz AA/d (<2 drinks/d) were placed into the abstainer/low consumption group. Women consuming 1.00 to 2.99 oz AA/d (25.99 drinks) were classified as moderate drinkers. Finally, women consuming ≥3.00 oz AA/d (≥6 drinks) were considered heavy drinkers. Sixty-seven percent of all women used substances other than alcohol. The likelihood of smoking varied by alcohol group: χ2(2, n = 145) = 12.62, P < .01. Women drinking moderate or heavy amounts of alcohol were more likely to smoke. Among all women who did smoke, the number of cigarettes smoked per day did not vary by alcohol group: F(2, 94) = 2.81, P > .07. The likelihood of using marijuana (χ2[2, n = 150] = 12.81, P < .01]) and cocaine (χ2[2, n = 150] = 10.00, P < .01) also varied by alcohol group. Women consuming heavy amounts of alcohol were more likely than the abstainer/low consumption group to use marijuana (χ2[1, n = 116] = 9.04, P < .01) and cocaine (χ2[1, n = 116] = 9.91, P < .01). Women consuming moderate amounts of alcohol were more likely to use marijuana (χ2[1, n = 122] = 8.70, P < .01), but not cocaine (χ2([1, n = 122] = .61) compared with the abstainer/low consumption group. Among women who used marijuana (F[2, 35] = .31, P > .74) or cocaine (F[2, 26] = .90, P > .42) the number of times it was used per week did not vary by alcohol group. The prevalence of other drug use did not vary by alcohol group.
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Table I. Descriptive statistics for maternal reports of alcohol consumption at conception
AA/d AA/d Abstainer/low Moderate Heavy
n
M
SD
Minimum
Maximum
Skew
155
2.07
5.36
0
58.56
8.12
92 34 29
.23 1.86 8.16
.33 .57 10.39
0 1.01 3.51
.99 2.88 58.56
1.10 .09 4.43
M, Mean; SD, standard deviation; AA/d, ounces of absolute alcohol consumed per day.
Table II. Sample demographic information Alcohol group Abstainer/low
Moderate
Maternal age* (y) 25.80 (5.58) 25.71 (5.05) Gravida† 2.68 (1.69) 2.94 (1.76) Parity‡ .91 (1.17) .79 (.95) Ethnicity (%) African American 4.35 5.90 American Indian 4.35 5.90 Asian 0.00 2.90 Caucasian 40.22 55.90 Hispanic 18.48 17.60 Other/unknown 32.61 11.80
Heavy 26.56 (6.16) 3.21 (2.13) 1.04 (1.23) 0.00 7.10 3.60 57.10 14.30 17.90
*n = 150. †n = 152. ‡n = 151.
Demographic information is presented in Table II. Gravida and parity were not significantly correlated with alcohol group, drug use (Table III), or the standardized brain measurements. Demographic variables were evaluated as predictors of brain structure, but were never significant, and therefore not mentioned later in the article. Descriptive information for the brain measurements is presented in Table IV. Correlations between brain measurements and alcohol and drug consumption are shown in Table V. Univariate correlations indicated that only FL and T2C were related to alcohol consumption. Other drug exposure (ie, cigarettes, marijuana, cocaine, methamphetamines) was not related to any of the brain measurements. These variables were evaluated as predictors of brain structure, but were not significant and therefore not mentioned later in the article. The significant correlations between alcohol consumption, FL, and T2C were followed up with regression analyses. Cigarette exposure and the interaction between cigarette use (no. per day) and alcohol group were also entered into the regression models because there was pervasive use of cigarettes across the sample. The regression analyses examined whether there was a disproportionate effect of alcohol exposure on the frontal cortex, which would suggest the frontal cortex has an increased vulnerability to the teratogenic effects of alcohol. Relationship between FL and alcohol consumption. Alcohol group, TCD, BPD, T2C, the number of cigarettes
smoked per day, and the cigarette by alcohol group interaction were entered into a stepwise regression analysis to determine the best predictors of FL. One multivariate outlier, the fetus of the woman reporting 58.56 oz AA/d at conception, was identified and excluded. T2C, TCD, alcohol group, and the alcohol by cigarette interaction were significant predictors, accounting for 25.4% of the variance in FL (F[4, 111] = 9.47, P < .001 (Table VI). Thus, even after including the size of other brain structures, alcohol consumption still accounted for a significant amount of the variance in FL. Although regression models are useful, assessing their clinical significance can be difficult. To explore the impact of alcohol exposure on the growth of the frontal lobe, we chose the 25th (FL25 ) and 10th (FL10) percentiles as criteria indicative of heightened risk. χ2 analyses indicated that the rates of an FL below the criterion increased significantly with alcohol exposure (Table VII). Previous research18, 19 has suggested that the neurobehavioral effects of prenatal alcohol exposure may be heightened if maternal age is >30 years. To explore this possibility, we examined the moderate and heavily exposed cases, all of whom were exposed to at least 1 oz AA/d at conception, to determine whether the risk of an FL below the 25th or 10th percentiles increased if maternal age was ≥30 years. χ2 analyses indicated that in alcohol-exposed fetuses, maternal age ≥30 years increased the risk of an FL below the 25th percentile, (χ2[1, n = 55] = 5.91; P < .02; odds ratio, 4.5). Maternal age ≥30 years marginally increased the risk of an FL below the 10th percentile, (χ 2[1, n = 55] = 3.18; P < .07; odds ratio, 3.5). These odds ratios demonstrate a substantial interactive risk. While alcohol exposure in isolation was associated with reductions in the size of the frontal cortex, this effect was heightened when maternal age was ≥30 years. Relationship between T2C and alcohol consumption. Alcohol group, FL, TCD, BPD, and the alcohol by cigarette exposure interaction were entered into a stepwise regression analysis to determine the best predictors of T2C (Table VI). BPD and FL entered the model accounting for 15.7% of the variance in T2C: F(2, 114) = 10.62, P < .001. Alcohol exposure and the alcohol by cigarette exposure interaction were not significant predictors. χ2 analyses examined whether the risk of a reduction in the size of the T2C increased with alcohol exposure. The
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Table III. Pearson correlations between maternal demographic variables and drug and alcohol exposure
Maternal age Gravida Parity Cigarette Marijuana Cocaine Alcohol group
Maternal age
Gravida
Parity
Cigarette
Marijuana
Cocaine
Alcohol group
— .406* .405* .071 –.033 .007 .043
— .710* .099 –.030 .118 .117
— .049 –.080 .061 .025
— .180† .171† .309*
— .398* .215*
— .172†
—
*P < .01. †P < .05.
Table IV. Descriptive statistics for average standardized TCD, T2C, FL, and BPD measurements by alcohol group n TCD Abstainer/low Moderate Heavy T2C Abstainer/low Moderate Heavy FL Abstainer/low Moderate Heavy BPD Abstainer/low Moderate Heavy
M*
Table V. Pearson correlations between standardized brain measurements and drug and alcohol exposure TCD
T2C
FL
BPD
— .267* .266* .167† –.062 .079 .115 –.040
— .339* .295* –.093 –.079 .021 –.139†
— .060 .043 –.035 –.014 –.281*
— .049 .073 .047 –.027
SD
86 32 27
.08 .02 .01
.81 .64 .72
86 31 26
.12 –.15 –.12
.82 .81 .75
86 31 26
.17 .04 –.68
.97 1.04 1.15
86 31 26
.06 .05 .00
.76 .84 .65
Sample sizes reflect the number of women per group for whom at least 1 measurement of a given structure could be obtained. TCD, Transcerebellar diameter; T2C, thalamus to inner calvarium; FL, frontal lobe; BPD, biparietal diameter; M, mean; SD, standard deviation. *Z scores are presented. Negative scores indicate that the average standardized length of the structure is shorter than expected.
likelihood of a T2C below the 25th or 10th percentile did not increase as a function of alcohol exposure. Thus, the area between the back of the thalamus and the frontal cortex was not as sensitive to the effects of prenatal alcohol exposure as the frontal cortex alone. The T2C measure may be less sensitive to the effects of alcohol exposure because it included the length of multiple structures, such as the thalamic nuclei, the cerebral peduncles, and the hippocampus, each of which could vary in their sensitivity to the effects of prenatal alcohol exposure. Comment Data from this study represent the first time that ultrasonographically identifiable alcohol-related structural differences have been documented during pregnancy in living human fetuses. Previous studies on alcohol effects have used spontaneously aborted fetuses that were likely to be more severely affected because they were not viable.
TCD T2C FL BPD Cigarettes Marijuana Cocaine Alcohol group
TCD, Transcerebellar diameter; T2C, thalamus to inner calvarium; FL, frontal lobe; BPD, biparietal diameter. *P < .01. †P < .10.
Table VI. Summary of stepwise regression analyses predicting FL and T2C Dependent variable FL
T2C
Variable entered Constant T2C Alcohol group Alcohol group × cigarette TCD Constant BPD FL
B
SE B
β
.636 .404 –.497 .001
.203 .109 .136 .004
— .314 –.376 .246
.267 –.080 .306 .186
.116 .069 .100 .064
.194 — .266 .254
FL, Frontal lobe; T2C, thalamus to inner calvarium; B, unstandardized regression coefficient; SE B, standard error of B; , standardized regression coefficient. TCD, transcerebellar diameter; BPD, biparietal diameter.
Further, imaging studies have only used severely affected children. Most of the children in earlier imaging studies had microcephaly and intelligence scores in the mental retardation range, indicating they were on the severe end of the spectrum. The current sample did not appear to be as severely affected; the alcohol-exposed fetuses were not microcephalic. If microcephaly were present, one would expect a negative relationship between alcohol exposure and the size of the BPD and the TCD, because both are typically highly correlated with gestational age and head circumference. These negative relationships were not found.
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Table VII. Descriptive statistics for the percent of cases with FL below 25th or 10th percentiles Criteria 25th Percentile
10th Percentile
Alcohol group FL25 Abstainer/low Moderate Heavy FL10 Abstainer/low Moderate Heavy
Cases below criteria (%)
Odds ratio*
χ2 χ2(2, n = 143) = 7.52, P < .03
19.77 22.58 46.15
1.18 3.48
4.65 12.90 23.08
3.04 6.15
χ2(2, n = 143) = 8.11, P < .02
FL, Frontal lobe. *Odds ratios were calculated by comparing the moderate and heavy exposure groups individually to the abstainer/low group.
Although the current sample appears to be less severely affected, one could still be concerned that the findings were driven primarily by 1 or more overly influential cases. There was 1 participant who reported an excessively high level of alcohol consumption at conception. It is possible that the woman over-reported her alcohol consumption. However, her fetus was the most severely impacted, as it had the smallest average standardized FL measurement of any fetus (z score = –4.20). Obviously, this case had the potential to be overly influential. However, this case was the multivariate outlier identified and eliminated in the regression analyses and therefore had no influence on the findings. On the basis of the findings, it appears that there was a disproportionate effect of alcohol on the frontal cortex rather than a global effect on the brain. Surprisingly, 46% of heavily exposed fetuses had a frontal cortex length below the 25th percentile. In contrast, only 20% of nonexposed fetuses were below this criterion. When the 10th percentile was used as a criterion, the results were just as striking. The finding that reductions in specific brain structures, but not global brain size, were associated with prenatal alcohol exposure was not entirely surprising. Microcephaly is observed only in the most severely affected children. It would be surprising if there were no effect on the brain except when microcephaly occurs. Recently, Persutte12 argued that a shortening of the frontal cortex during gestation might be a precursor to microcephaly. Reductions in the frontal cortex observed in this sample were consistent with neuropsychologic10 and anecdotal reports20 of executive functioning deficits in alcoholexposed children. Executive functioning problems include difficulties updating and manipulating information in working memory, inhibiting information and actions, and sustaining attention.21 Executive functioning problems can disrupt the child’s functioning within family, school, and peer settings. These types of deficits are present in a variety of developmental disorders, such as attention deficit-hyperactivity disorder, autism, and early treated phenylketonuria.21-23 Further, executive functioning deficits can cause significant difficulties even when the child has an IQ score within the normal range.
While alcohol exposure was predictive of the length of the frontal cortex, a relatively small amount of variance was accounted for in the regression model. Although one would not expect to see a large correlation between exposure and the size of brain structures, it is possible that the relationship was limited by the measures of alcohol consumption used. We reported alcohol consumption at conception because consumption across the duration of the pregnancy could not be quantified for many participants. Alcohol consumption limited to the at-conception period is unlikely to cause a reduction in size specific to the frontal cortex because individual brain structures are not differentiated at that time. Although drinking at conception is correlated with drinking during the pregnancy, solely using at-conception drinking limits our ability to examine the effects of prenatal alcohol exposure at different times throughout the pregnancy. For example, it is not known how many of the women continued to consume alcohol through the third trimester brain growth spurt. It is likely that consumption during the third trimester would result in the most profound reductions in brain size. In contrast, if a woman consumed alcohol early in pregnancy, but abstained from drinking later in pregnancy, it is possible that the brain could compensate. Several studies provide indirect support for this hypothesis by showing that the magnitude of neurologic and neurobehavioral deficits is reduced if women do not drink during the third trimester.24, 25 Further studies need to examine whether the fetal brain can compensate for early exposure if maternal consumption ceases during pregnancy. If it can be demonstrated that both alcohol-induced structural changes and neuronal compensation after the cessation of drinking can be detected, ultrasonography could become a powerful primary intervention tool for physicians to concretely demonstrate the effects of pregnancy drinking and to encourage women who drink during pregnancy to seek treatment. The current study demonstrated that ultrasonography can be used to document in utero reductions in specific brain structures associated with alcohol exposure. It is not known whether these findings will be predictive of later
742 Wass, Persutte, and Hobbins
development. We do not know whether the alcohol-related changes in frontal lobe development will translate into meaningful differences in neurobehavioral functioning. If it can be demonstrated that alcohol-related changes in brain structure are predictive of postnatal development of the child, ultrasonography could become a powerful tool not only in the prenatal diagnosis of teratogeninduced disorders, but also in examining the link between brain development and behavior during the early formative years. We thank Dr Marshall Haith, Dr Sandra Jacobson, and Dr Joseph Jacobson who contributed much toward the successful completion of this research.
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