Pregnant women are often considered a vulnerable population during disasters, both natural and chemical [1
], and for this reason, the effects of the Gulf oil spill on pregnant women are of particular concern. Although a large number of studies have examined the effect of disaster on birth outcomes, such as low birthweight or preterm birth [2
], and an additional line of research examines its effects on the infants [3
], relatively few studies have assessed how disaster might affect maternal health. In terms of major medical complications, gestational diabetes (GDM) and hypertensive disorders of pregnancy (including pre-eclampsia (PE) and pregnancy-induced hypertension (PIH)) have been examined in a few studies, with mixed results [4
]; some studies show an increase, others show no effect.
Any disaster could be hypothesized to trigger such complications via endocrine or behavioral pathways: stress is associated with increased blood pressure and glucose levels [9
]. Disaster may also change the availability of healthy foods and motivation available for healthy eating patterns, or cause shifts in smoking prevalence [12
]. When considering effects of an oil spill specifically, chemical exposures are also of concern [20
]. Again, evidence is limited, but some pollutants associated with the oil spill, including heavy metals and products of combustion, have been associated with GDM and PIH [21
]. Although few studies have considered nausea/vomiting for pregnancy specifically, studies of workers in the petrochemical industry [24
] and oil spill cleanup workers have reported nausea/vomiting (or dizziness) [25
In this analysis, we examine the association between self-reported exposure to the physical and social/economic effects of the Gulf oil spill, and pregnancy complications.
The study population was predominantly <30 years old, black, and with high BMI (Table 1
). Approximately half reported some sort of exposure to or effect of the oil spill, most often financial. GDM and PE were reported by 7–9%; hypertension by 21%, and nausea/vomiting by 70–75%.
Any exposure to the oil spill was associated with increased risk of GDM (aOR 1.84, 95% CI: 1.14–2.99; Table 2
), but no individual contributor could be identified as contributing strongly to that. No associations were found with hypertensive disorders (Table 3
). Overall, increased nausea/vomiting post-oil spill was found (aOR 1.60, 95% CI: 1.12–2.27; Table 4
) in the sample with both pre- and post-oil spill pregnancies, and particularly with income loss (aOR 1.75, 95% CI: 1.07–2.85).
Overall, few interactions were found between timing of pregnancy and oil spill exposure, suggesting that reported oil spill exposure did not more strongly predict these outcomes for pregnancies that occurred after the oil spill. In the cases where there was a suggestion of an interaction (p
< 0.15), effects were stronger for pregnancies prior to the oil spill for gestational diabetes (Table S1
). The relationship between contact with the oil and nausea/vomiting was statistically different, and stronger, for pregnancies after the spill, but was not statistically significant overall (pre-oil spill aOR 0.83, 95% CI: 0.53–1.29; post-oil spill, aOR 1.48, 95% CI: 0.81–2.69; p
for interaction = 0.05; Table S2
The medical records analysis did not indicate any associations with gestational diabetes (Table S3
). Hypertensive disorders were more common only in those reporting contact with oil (aOR 3.13, 95% CI: 1.05–9.35).
This analysis did not find evidence of strong associations between oil spill exposure and pregnancy complications, with what few associations there were largely being equally strong for pregnancies occurring prior to the oil spill as after. Few studies have previously assessed the association of maternal pregnancy complications with either chemical or natural disaster, and results are conflicting. While exposure to the 2010 Chile earthquake was associated with increased gestational diabetes if exposed in the first semester (OR 3.9, 95% CI: 1.0–15.5) [4
], the exposure to the 2003 Canberra Wildfires were not [4
]. An increase in eclampsia was noted after the 1997 Red River flood in North Dakota [7
], but a decline in eclampsia was noted after Hurricane Katrina [8
]. Individual differences may contribute to the risk: stress and certain coping styles in the aftermath of Hurricane Katrina were associated with gestational diabetes and pregnancy-induced hypertension [6
]. We are not aware of any studies specifically addressing nausea/vomiting during pregnancy; a study of pregnant women near the Hebei Spirit oil spill in South Korea found an increase in minor somatic symptoms, although not nausea/vomiting [30
]. Nausea/vomiting during pregnancy is associated with stress and psychological symptoms, although the direction of the association is not clear [31
]. Our results are not inconsistent with an increased risk, but do not demonstrate that definitively.
Biological and behavioral pathways for an effect on pregnancy complications can be hypothesized. Disaster has been associated with changes in glucose levels, both in diagnosed diabetics [34
] and undiagnosed or unaffected people [10
]. Work in the petrochemical industry has also been associated with higher blood glucose [37
]. Some studies have also found increased blood pressure with exposure to disaster stress or exposure to petroleum or related products [38
]. We did find an increase in recorded hypertensive disorders in the medical records of the pregnant women among those who reported contact with oil, although not with other oil spill exposures. This association should be investigated in more detail in studies with more detailed exposure and outcome measures. A less regulated diet, less physical activity, and weight gain—strong risk factors for GDM and PIH—are plausible consequences of social and economic stress. A lack of effect is also plausible. Women in this study were interviewed largely two to four years after the oil spill itself, so short-term symptoms such as nausea may not have been accurately remembered. Nausea is quite common during pregnancy in any case; the oil spill may not have had a strong enough effect to distinguish it from the background levels, and we did not ask about severity. Most women did not live near enough to the oil spill to smell it, which has been associated with reporting physical symptoms [42
]. Truly assessing whether an oil spill was exacerbating mild cases of nausea would probably require detailed, prospective data collection.
Strengths of the study include a relatively unselected population, with no particular reason to over or under-report exposures and outcomes; a reasonably large sample size; and the opportunity for examining pregnancies that occurred prior to the oil spill as a negative control. We performed as systematic and thorough an assessment of outcomes and exposures as possible within the study design; still, measurement error is likely present. Pregnancy complications are difficult to measure. Previous studies often use vital records data, which usually under-reports complications and has limited information on some important complications, like pre-eclampsia (only eclampsia—quite rare—is reported on the standard birth certificate. Pre-eclampsia is combined with pregnancy-induced hypertension [43
]). Complications in this analysis were measured primarily via self-report. Previous studies have found maternal self-report to be accurate for reports of gestational diabetes (GDM) (specificity = 98%, sensitivity = 92%) [44
] and highly specific (>90%) for hypertensive disorders [45
]. Nonetheless, self-report is unlikely to overlap completely with medical diagnosis. Besides simply mistaken or misunderstood recall of complications, women who had hypertension prior to the pregnancy, or who were told that their blood pressure seemed a little high at a prenatal visit, or who were asked to come back after glucose tolerance screening but were not diagnosed with diabetes, might have correctly answered yes to the questions as posed. In most cases, women were interviewed during pregnancy prior to likely onset of GDM or hypertensive complications (thus, those pregnancies are omitted from those analyses). Nausea and vomiting, unless severe enough to require hospitalization, have no other plausible source of information beyond self-report. In certain types of disaster, disruption of the health care system or over-diagnosis could be causes for bias; these are unlikely for this particular topic. Still, recall bias, or reporting error, is possible. If not connected with exposure, the most likely consequence of this error is bias towards the null.
Other limitations of the study include the fact that the post-oil spill and pre- and post-samples are different, most obviously by conditioning on gravidity, and the age and gravidity at a second pregnancy is by definition larger than at the first. Thus, the earlier pregnancies are an imperfect control and residual confounding is possible, although previous analysis of ours found no association between oil spill exposure and fertility [46
]. Similarly, oil spill exposure is self-reported, which likely leads to misclassification or, at least, inexactness in measurement; the most likely consequence of this is bias towards the null. Too few women were pregnant during the spill to examine timing of exposure relative to the pregnancies. Likewise, many analyses were conducted in the course of this study, and chance findings are a possibility. Similarly, the sample size was insufficient to detect weaker associations.