Objective
Marijuana use is becoming increasingly common in the obstetric population; however, it is unknown whether it is associated with poor neonatal outcomes. We sought to determine the prevalence and risk factors for marijuana use in pregnancy and to evaluate whether marijuana use is independently associated with poor neonatal outcomes.
Study Design
This was a retrospective cohort study of all consecutive, nonanomalous, term deliveries at 1 institution over a 4-year study period. Women with marijuana use during pregnancy, either by self-report or positive urine drug screen, were compared with women who did not use marijuana. The primary outcome was a composite neonatal morbidity including birthweight less than 2500 g, neonatal intensive care unit admission, 5-minute Apgar score less than 7, and umbilical artery pH less than 7.10. Univariate, bivariate, and multiple logistic regression analyses were performed.
Results
Among the 8138 women in the cohort, 680 (8.4%) used marijuana during pregnancy. Women who used marijuana were younger; more likely to be of African American race; have inadequate prenatal care; and use tobacco, alcohol, and other drugs. Medical comorbidities did not differ between groups. After adjusting for smoking, other drug use, and African American race, the composite and all individual markers of poor neonatal outcome were not significantly higher among women who used marijuana during pregnancy.
Conclusion
Marijuana use is common in pregnancy but may not be an independent risk factor for poor neonatal outcomes in term pregnancies.
Marijuana is the most common illicit drug used during pregnancy. In the literature, the prevalence of marijuana use in pregnancy ranges from 2% to 27%, depending on the population studied and method of detection. Societal views of marijuana use are changing, and therefore, the rates of marijuana use are projected to increase further. Although still considered an illegal drug in most locations in the United States, marijuana use is now legal in a handful of states, with legislature pending in many others. However, surprisingly little is known about the effects of marijuana on neonatal outcomes in pregnancy.
The main chemical compound found in marijuana, delta 9 tetrahydrocannabinol (THC) readily crosses the placenta and is found in breast milk. Importantly, the THC potency in marijuana has increased 6- to 7-fold in the past 40 years. But the main metabolite of THC, 11-nor-9-carboxy-THC, does not cross the placenta. In addition, marijuana can be detected in the body for 30 days after use, potentially exposing the fetus for a prolonged period of time after a single use. Cannabinoid receptors are found in the brain and in the uterine decidua. Aside from the potential chemical effects of THC on the fetus, the effects on maternal respiratory and gas exchange physiology may be harmful to the fetus. Marijuana is usually smoked and inhaled and has been shown to lead to a 5-fold higher carbon monoxide level compared with smoking tobacco.
Prior studies have investigated selected obstetric and fetal outcomes such as preterm delivery, low birthweight, and stillbirth. In the current literature, the results regarding fetal and neonatal outcomes are conflicting. Many of the studies reporting association between marijuana and poor neonatal outcomes are confounded by other factors such as tobacco or drug use. Therefore, we sought to determine the effects of maternal marijuana use on neonatal morbidity, focusing on term infants, and adjusting for confounding factors.
Materials and Methods
We performed a retrospective cohort study of all consecutive term deliveries occurring over a 4-year student period from 2004 to 2008 at Washington University in St Louis Medical Center. Prior to initiating the study, approval was obtained from the Washington University Human Research Protection Board.
Inclusion criteria consisted of all women with term, nonanomalous, live, singleton pregnancies who underwent delivery at this tertiary care facility during the study period. Exclusion criteria were met for women with preterm deliveries, known fetal congenital anomalies, or multiple gestations.
For all women in the cohort, detailed demographic information was extracted from the medical record by trained obstetric research nurses. Data obtained included patient medical and surgical history, obstetric and gynecological history, prenatal history, antepartum records, delivery records, and postpartum records.
Marijuana use was defined as women who used marijuana at least once during pregnancy and was identified through self-report or positive urine drug screen. Two groups were defined: women who used marijuana during pregnancy and those who did not.
The primary outcome measures were composite neonatal morbidity and its individual components. Measures of neonatal morbidity included birthweight less than 2500 g, neonatal intensive care (NICU) admission, 5-minute Apgar score less than 7, and umbilical artery pH less than 7.10. Individual components of the composite were chosen for their clinical relevance as markers for morbidity in a term neonate. Infants with 1 or more morbidities were considered positive for neonatal composite morbidity. Infants with more than 1 criterion for neonatal morbidity were counted only once in the composite. Apgar scores were assigned clinically by the physician or nurse practitioner attending the delivery. Umbilical arterial blood gases were universally obtained immediately after delivery from an umbilical cord segment.
Baseline characteristics were compared between the study groups using a χ 2 or Fisher exact test for categorical variables and Student t or Mann-Whitney U test for continuous variables as appropriate. Normal distribution of continuous variables was tested by examination of the histogram as well as the Kolmogorov-Smirnov test.
Bivariate analyses were then performed to identify potentially confounding variables. Prevalence, relative risks, and 95% confidence intervals (CIs) were calculated for each of the primary outcomes. Multivariate logistic regression analyses were performed in a backward stepwise fashion controlling for potential confounding variables identified through the univariable and bivariate analysis. Only variables that were statistically significant were included in the final models. All statistical analyses were completed using STATA software package, version 12 (StataCorp, College Station, TX). Tests with P < .05 were considered significant.
Results
During the study period, 8138 women met all inclusion criteria. Among these women, 680 (8.4%) were found to use marijuana during pregnancy. When baseline characteristics were compared, women who used marijuana were younger, more likely to be of African American race, and have inadequate prenatal care. Additionally, marijuana users were also more likely to use tobacco, alcohol, and other drugs during pregnancy. More than 58% of marijuana users also used tobacco compared with 14.3% of the patients who did not use marijuana. Similarly, 10% of marijuana users concomitantly used other drugs, and 7.6% used alcohol. Medical comorbidities including hypertension and preeclampsia did not differ between the groups. Marijuana users had a slightly lower body mass index, although still in the obese range, and a lower rate of diabetes ( Table 1 ).
| Characteristic | Marijuana use (n = 680) | No marijuana use (n = 7458) | P value |
|---|---|---|---|
| Age | 24.0 ± 5.3 | 25.0 ± 6.1 | < .001 |
| African American race (n = 5863) | 87.1% | 70.7% | < .001 |
| BMI | 32.1 ± 7.2 | 32.7 ± 7.6 | .04 |
| Nulliparity (n = 3012) | 33.3% | 37.3% | .04 |
| Tobacco use (n = 1465) | 58.1% | 14.3% | < .001 |
| Alcohol use (n = 111) | 7.6% | 0.8% | < .001 |
| Other drug use (n = 220) | 10.0% | 2.0% | < .001 |
| Private insurance (n = 1255) | 2.5% | 16.6% | < .001 |
| Inadequate prenatal care (≤5 visits) (n = 1472) | 29.6% | 17.0% | < .001 |
| Hypertension (n = 945) | 11.9% | 11.6% | .80 |
| Preeclampsia (n = 505) | 6.2% | 6.2% | .97 |
| Diabetes (n = 418) | 3.1% | 5.3% | .01 |
A total of 674 patients (8.3%) had the composite outcome. The composite of neonatal morbidity was found in 11.6% of women who used marijuana compared with 8.0% of women who did not. In the unadjusted analysis, women who used marijuana had a 50% increased risk for the composite of neonatal morbidity (11.6% vs 8.0%; relative risk, 1.5; 95% CI, 1.2–1.8). However, after adjusting for smoking tobacco, other drug use, and African American race (maternal age, alcohol use, and diabetes did not contribute significantly to the explanatory model and were therefore not included in the final model), the composite neonatal morbidity was not significantly different between women who used marijuana during pregnancy and those who did not (composite adjusted odds ratio, 1.3; 95% CI, 0.96–1.6; P = .10).
Rates of individual components of the composite including birthweight less than 2500 g, neonatal intensive care admission, 5-minute Apgar less than 7, and umbilical artery pH less than 7.10 were not significantly different between groups ( Table 2 ).
