South African mothers' immediate and 5-year retrospective reports of drinking alcohol during pregnancy

Kodi B. Arfer, Mary J. O'Connor, Mark Tomlinson, and Mary Jane Rotheram-Borus
Created 23 Jan 2017 • Last modified 2 Sep 2017

Measuring prenatal drinking is usually accomplished with self-report, but it is unclear whether mothers give more accurate answers when asked while pregnant or some time after their pregnancy. There is also the question of whether to measure drinking in a dichotomous or continuous fashion. From a sample of 576 mothers around Cape Town, South Africa, we compared contemporaneous reports of prenatal drinking with 5-year retrospective reports, and dichotomous metrics (drinking or sober) with continuous metrics (fluid ounces of absolute alcohol drunk per day). Amounts increased over the 5-year period whereas dichotomous measures found mothers less likely to report drinking later. All four measures were weakly correlated with birth weight, birth height, child head circumference soon after birth, and child intelligence at age 5. Our results point to problems with self-report, particularly with this population, but suggest that investigators should choose between contemporaneous and retrospective report depending on whether they are concerned with amounts drunk or with total sobriety.

Acknowledgments: This study was funded by the National Institute on Alcohol Abuse and Alcoholism (1R01AA017104), the National Institute of Mental Health (T32MH109205), the UCLA Center for HIV Identification, Prevention and Treatment Services (P30MH58107), the UCLA Clinical and Translational Science Institute (UL1TR000124), and the UCLA Center for AIDS Research (P30AI028697).

Introduction

Drinking during pregnancy can lead to fetal alcohol spectrum disorder (FASD), which comprises a wide variety of detrimental consequences for the health of a child (Williams & Smith, 2015). Thus, measuring how much expectant mothers drink is important for public health, but mothers may be reluctant to admit their drinking to investigators. FASD is particularly common in the Western Cape Province of South Africa, with about 15% of children affected (May et al., 2013). We studied self-reports of drinking among mothers in this region, asked during pregnancy and 5 years after birth.

One strategy that might be expected to elicit more honest replies is to ask mothers about prenatal drinking long after the child is born, rather than while they are still pregnant. Mothers may feel less shame about past events, or less able to effectively deceive researchers when they have a child with obvious signs of FASD. On the other hand, mothers' memories of their drinking behavior should become less accurate over time, and their shame may be more acute once they have a visibly unhealthy child. Hence, it is not obvious whether mothers will be more honest, or will say they drink more, when asked contemporaneously or retrospectively.

Studies from Cleveland and Detroit hospitals asking mothers about prenatal drinking both during pregnancy and from 1 to 14 years after birth have found that mothers' reports of how much they drink are much more likely to increase than decrease (Ernhart, Morrow-Tlucak, Sokol, & Martier, 1988; Jacobson, Chiodo, Sokol, & Jacobson, 2002; Hannigan et al., 2010). In other words, within subjects, mothers report drinking more when interviewed retrospectively. However, past results are less consistent when drinking data is dichotomized into any drinking versus no drinking, rather than represented as ounces of alcohol. Comparing the sober consistency rate (the proportion of mothers who said they abstained retrospectively, among those who had also said they abstained contemporaneously) to the drinking consistency rate, one study (Hannigan et al., 2010) found greater sober consistency (80% vs. 70%), another (Ernhart et al., 1988) found greater drinking consistency (61% vs. 78%), and another (Jacobson et al., 2002) found very similar rates (78% vs. 80%). It is thus unclear whether retrospective report makes mothers more or less likely to admit drinking during pregnancy. Furthermore, it is unclear how well these results generalize outside the United States.

Why would one use a dichotomous measure of prenatal drinking rather than a continuous one? A dichotomous measure is easy to administer: it requires no prop beverage containers, definition of a standard drink, distinction between types of beverages because of their different concentrations of alcohol, or discernment of mothers' drinking patterns. Besides reducing potential variability in how mothers interpret questions, a dichotomous measure is less dependent on memory. A priori, people seem likely to misremember exactly how much, when, or what they drank, but should have little trouble remembering whether they drank at all. Finally, while there are certainly dose-dependent effects of alcohol on feti, the consensus of researchers is that no amount of alcohol during pregnancy is safe (Williams & Smith, 2015), so preventing prenatal drinking entirely, rather than merely reducing frequencies or amounts to a known nonzero safe level, is typically the goal of interventions.

In this study, we compare contemporaneous reports of prenatal drinking with 5-year retrospective reports among mothers in the Western Cape. We also compare dichotomous to continuous measures of drinking. Finally, we compare how these various ways of measuring drinking (contemporaneously or retrospectively, and dichotomously or continuous) are associated with child health. The overall goal is to better understand the strengths and weaknesses of these strategies, for the benefit of future investigation into prenatal drinking.

Method

We use data from a cluster-randomized controlled trial of a mentor intervention for new mothers and their babies in the area of Cape Town, South Africa (see le Roux et al., 2013; ClinicalTrials.gov registration number NCT00972699). Mothers in both conditions received comprehensive healthcare at clinics. Mothers in the experimental condition additionally received regular home visits from another mother who was a trained community health worker and a positive deviant, having had a healthy baby herself. Conditions were randomly assigned per neighborhood. In this paper, because we do not wish our results to be affected by the experimental intervention, we consider only the mothers in the control group.

Our analysis draws primarily from assessments at two timepoints, baseline and 5 years after birth. At the time of the baseline assessment (T1), mothers were 3 to 40 weeks pregnant (mean 26 weeks). Mothers were asked "How often did you use alcohol in the month before you found out you were pregnant?" and "During the month before you found out you were pregnant, counting all types of alcohol combined, how many drinks did you USUALLY have on days when you drank alcohol?". (The second question was skipped if the answer to the first was "Never". We asked mothers about the month before they recognized their pregnancy because we expected they would be more candid about this period, and that they would notice their pregnancies relatively late. We also asked mothers about drinking after they had recognized their pregnancy, but those questions are not analyzed here.) At the 5-year follow-up (T2), mothers were asked the same questions, except the word "pregnant" was replaced with "pregnant with" followed by the child's name. To define for the mother how large a drink was, the interviewer showed prop beverage containers including a beer bottle, a 250-mL wine glass, and a shot glass; we aimed to represent the American standard drink of 0.6 fl oz (14 g) of ethanol. Table 1 shows the response options for the two questions and how they are coded. For a dichotomous measure of drinking, we code mothers as sober if they answered "Never" and drinking otherwise. To compute fluid ounces of absolute alcohol drunk per day (AA/day), a measure we chose to aid comparison with previous research, we multiply 0.6 by the numeric frequency code by the numeric amount code.

Mothers were also asked questions about drinking during pregnancy at another timepoint T1.5, between T1 and T2, after birth and before the children were more than 4 months old. These questions, however, asked about "the last month, before your baby was born". Because they are not directly comparable to the T1 and T2 questions analyzed here, we exclude them from analysis.

Table 1. The response options for the two drinking questions, and how we represent them as numeric codes.
Response option Code
Drinking frequency  
     Never 0.00
     Less than once a month 0.02
     Once a month 0.05
     2 to 3 times a month 0.10
     Once a week 0.20
     2 times a week 0.50
     3 to 4 times a week 0.50
     Nearly every day 0.70
     Every day 1.00
Number of drinks  
     1 or 2 1.50
     3 or 4 3.50
     5 or 6 5.50
     7,8 or 9 8.00
     10 or more 10.00

We consider four outcomes. At T1.5, mothers reported the weight and height of their children at birth, which we mean-center within child sex for analysis. We measured the current circumference of children's heads, and calculated their sex- and age-specific z-scores using WHO norms. At T2, children were administered the Kaufman Assessment Battery for Children (Lichtenberger & Kaufman, 2010). Our analyses use the Mental Processing Index (MPI), which measures general mental processing ability (i.e., intelligence) and excludes an assessment of acquired knowledge. Like traditional intelligence measures, the MPI is normed to have a mean of 100 and an SD of 15.

Results

Data-analysis code can be found at http://arfer.net/projects/philani.

Table 2. Mothers' reports of drinking at the two timepoints, baseline (T1) and 5 years after the child's birth (T2). Mothers who are "consistent" are those who gave the same dichotomous answers at the two timepoints. AA/day = fluid ounces of absolute alcohol per day, CI = confidence interval
Dichotomous (drinking vs. sober)  
     Mothers reporting, either timepoint 576
          Percent drinking, T1 26%
          Percent drinking, T2 21%
     Mothers reporting, both timepoints 366
          Percent consistent, among sober at T1 92%
               95% Jeffreys CI [88%, 95%]
          Percent consistent, among drinking at T1 63%
               95% Jeffreys CI [53%, 72%]
Continuous (AA/day)  
     Mothers reporting, either timepoint 576
          Mean, T1 0.10
          Mean, T2 0.19
          Maximum, T1 3.00
          Maximum, T2 3.36
     Mothers reporting, both timepoints 365
          Percent increasing from T1 to T2 18%
          Percent decreasing from T1 to T2 12%
          Mean change 0.12
               95% bootstrap CI [0.07, 0.18]
          Mean absolute change 0.19

Table 2 compares reports of drinking at T1 and T2. Coding drinking dichotomously, we see that mothers reported drinking at a slightly higher rate at T1 than T2, and mothers who stated they were sober at T1 were much more likely to repeat their answer at T2 than mothers who stated they drank at T1. By contrast, when we code drinking in terms of AA/day, means are higher at T2 than T1, and mothers were slightly more likely to increase their reported amount of drinking than decrease it; the mean change was positive, at .12 AA/day. The near-doubling of between-subjects means (.10 to .19 AA/day) is mirrored by a fourfold increase in the proportion of mothers who report drinking at least 3 drinks/day (1.8 AA/day), from 0.8% (4 mothers) to 3.4% (15 mothers).

Table 3. Kendall correlations of drinking measures with birth characteristics, head circumference after birth (WHO z-score for age and sex) and year-5 child intelligence (Kaufman mental processing index). Measures of drinking during pregnancy were taken at baseline (T1) or 5 years after the child's birth (T2), and used dichotomous (drinking or not drinking) or continuous (fluid ounces of absolute alcohol per day) coding. Confidence intervals (95%) are computed with the bias-corrected accelerated non-parametric bootstrap (Efron & Tibshirani, 1993).
Model Birth weight Birth height Head circumference Intelligence
(Sample size) 338 214 364 284
T1, dichotomous -.0441 [-.13, +.04] -.0323 [-.14, +.07] -.0824 [-.16,  .00] -.0538 [-.15, +.04]
T1, continuous -.0494 [-.13, +.03] -.0332 [-.13, +.06] -.0817 [-.16,  .00] -.0504 [-.14, +.04]
T2, dichotomous -.0602 [-.14, +.03] -.0045 [-.11, +.10] -.0616 [-.15, +.02] -.0711 [-.16, +.03]
T2, continuous -.0613 [-.14, +.02] -.0015 [-.10, +.10] -.0673 [-.15, +.02] -.0668 [-.16, +.03]

Table 3 shows how retrospective versus contemporaneous reports and dichotomous versus continuous coding affect the correlation of drinking with child health. The correlations are all negative, as expected, but small. The most-correlated measure differs by outcome, but the differences within outcomes are very small, and all the confidence intervals are largely overlapping. We also examined how well the four drinking measures could predict outcomes with linear regression models, evaluated with cross-validated mean square error. None of the estimates of predictive accuracy meaningfully improved upon baseline. We omit details for brevity.

Discussion

We find that among mothers in the Western Cape, as in other populations (Ernhart et al., 1988; Jacobson et al., 2002; Hannigan et al., 2010), mothers report drinking greater amounts prenatally when questioned after rather than during their pregnancy. By contrast, when answers are coded dichotomously as drinking or sober, mothers are more likely to say they drank when interviewed contemporaneously. These findings suggest that the question of when to ask mothers about prenatal drinking depends on the details of how drinking is measured. One possible explanation for this discrepancy is that women interviewed retrospectively tend to round small amounts to 0 and other amounts upwards, perhaps because of memory errors. Such an effect would be a sort of opposite of the finding in decision-making research that people overweight probabilities slightly more than 0 and underweight probabilities slightly less than 1 (Rottenstreich & Hsee, 2001).

The weak correlations of prenatal drinking reports with child outcomes are puzzling. They could indicate that these mothers' reports about prenatal drinking are highly inaccurate, but there could just as well be other, much larger sources of variation in body size and intelligence obscuring the true relationships. Ultimately, the only way to judge the accuracy of drinking reports is to compare them to some other measure of drinking, such as direct observation, informant report, or biomarkers. We found in a study of young men in nearby Cape Town (Arfer et al., 2017) that only 61% of men who drank in the last three days, according to a urine test, admitted as much in an interview. Still less accurate self-report might be expected for the more dangerous and stigmatized activity of drinking while pregnant. Overall, while our results suggest that contemporaneous report is better for dichotomous measures and retrospective report for continuous measures, they also suggest that self-report is simply not accurate enough for this population.

One might suspect that retrospective reports of prenatal drinking are determined mostly by current drinking (Jacobson et al., 2002). That is, mothers report that they drank prenatally however much they are drinking at the time they are asked. However, we found in an American sample (O'Connor & Paley, 2006) that retrospective reports of prenatal drinking were more correlated with child head circumference (r = −.44) and number of physical anomalies (r = .39) than reports of current drinking were correlated with the same outcomes (rs = .21, −.14). Hence, retrospective reports do not seem to be reflections of current drinking habits alone.

Although our sample is large overall, we did not specifically recruit mothers who reported high drinking levels during pregnancy. Hence, among mothers who reported any drinking, we observed means of only .38 AA/day at T1 and .92 AA/day at T2, and only a few mothers reported heavy prenatal drinking (e.g., only 4 mothers at T1 and 15 mothers at T2 reported drinking at least 3 standard drinks or 1.8 AA/day). It follows that our findings do not say much about heavier prenatal drinkers. Another possible limitation is that we measured drinking with a few short questions rather than a detailed interview or timeline follow-back procedure, which may have aggravated underreporting of drinking.

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