The Protective Effect of Pregnancy on Risk for Drug Abuse: A Population, Co-Relative, Co-Spouse, and Within-Individual Analysis

Abstract

Objective: The authors sought to determine whether pregnancy is an intrinsic motivator for cessation of drug abuse.

Method: The authors conducted prospective cohort, co-relative, co-spouse, and within-person analyses of registration for drug abuse during pregnancy among Swedish women born between 1980 and 1990 who gave birth between ages 20 and 35 (N=149,512). Drug abuse was assessed from medical, criminal, and pharmacy registries.

Results: In the population, rates of drug abuse were lower during pregnancy (unadjusted odds ratio=0.67, 95% CI=0.60, 0.74). Compared with population results, the negative association between pregnancy and drug abuse was moderately stronger in cousins (odds ratio=0.49, 95% CI=0.39, 0.62) and substantially stronger in siblings (odds ratio=0.35, 95% CI=0.24, 0.51) discordant for pregnancy. The estimated odds ratio for drug abuse in pregnancy-discordant monozygotic twins was even stronger, at 0.17 (95% CI=0.10, 0.31). Within individuals, the odds ratio for drug abuse while pregnant compared with an equivalent prepregnancy interval was similar to that seen in pregnancy-discordant monozygotic twins, at 0.22 (95% CI=0.19, 0.26). Compared with cohabiting fathers, mothers had a greater reduction in risk for drug abuse during pregnancy (odds ratio=0.40, 95% CI=0.34, 0.47). Pregnancy was more protective in women with low parental education and without a cohabiting, actively drug-abusing father. Compared with prepregnancy baseline, within-individual analyses indicate that risk for drug abuse is also substantially reduced in the postpartum period, for example, the odds ratio for postpartum days 0-242 was 0.13 (95% CI=0.11, 0.16).

Conclusions: Risk for drug abuse in women is substantially reduced during pregnancy. Multiple analyses suggest that this association is largely causal, suggesting that pregnancy is indeed a strong intrinsic motivator for drug abuse cessation. Similar strong protective effects may be present in the immediate postpartum period. Our results have implications for our etiologic models of drug abuse and especially for contingency management programs seeking to reduce drug abuse risk.

Keywords: Epidemiology; Psychoactive Substance Use Disorder.

Figure 1

The Association between Pregnancy and Risk for Drug Abuse – as assessed by an Odds Ratio (± 95% Confidence Intervals) – in the general population, cousins, siblings and monozygotic twins discordant for pregnancy, and within-individuals (comparing matched periods before and during pregnancy) for a first and second pregnancy. The odds ratios are all “raw’ – that is estimated from models without covariates.

Figure 2

Estimated Risk for Drug Abuse (DA) During the Control Periods and Pregnancy as a Function of Four Potential Moderators: Prior Crime, Parental Drug Abuse, Prior Drug Abuse (in the Pregnant mother) and Marital Status. These estimates are from logistic regression models with interaction terms (as seen in table 3).