Developmental outcomes of 3,4-methylenedioxymethamphetamine (ecstasy)-exposed infants in the UK

Recreational stimulant use, including 3,4-methylenedioxymethamphetamine (MDMA, "ecstasy"), is common among young adults worldwide, and a growing proportion of users are women of childbearing age. Earlier research has documented a range of psychological and physiological effects of MDMA in adults and animal evidence suggests prenatal MDMA exposure can impair memory and learning. In addition, maternal effects of MDMA use (for example hyperthermia, raised cortisol, appetite and sleep disruption) and a prior teratology signal in the UK raised concern that fetal MDMA exposure might affect neurodevelopment, particularly functions subserved by the serotonin system. Singer and colleagues set out to address a gap in human data by reporting findings from the first prospective longitudinal study of infants prenatally exposed to MDMA in the UK. The study tested the hypothesis that children exposed in utero to MDMA would show poorer developmental outcomes across the first 2 years of life than nonexposed children, after controlling for other drug exposures and relevant confounders.

The Drugs and Infancy Study was a prospective longitudinal cohort funded by the US National Institute on Drug Abuse and conducted in the UK between 2001 and 2005. Participants were volunteers recruited via midwives, clinic leaflets and advertisements for a study of recreational drug use in pregnancy; women with HIV, an intellectual disability (IQ < 70), severe psychiatric or medical illness, or infants with diagnosable illness at birth were excluded. Ninety-six mother–infant dyads were followed: 28 with maternal MDMA exposure and 68 without MDMA exposure. MDMA status and detailed patterns of use of MDMA, tobacco, cannabis, alcohol and cocaine were obtained by trained interviewers on three occasions during pregnancy or shortly after birth, using an adapted instrument that recorded lifetime use and trimester-specific use. Infants were assessed at 1, 4, 12, 18 and 24 months. Primary developmental measures included the Bayley Scales of Infant Development (Mental Development Index, MDI; Psychomotor Development Index, PDI; and Behavioural Rating Scales, BRS). Additional measures included the Neonatal Intensive Care Unit Network Neurobehavioral Scales (at 1 month), the Alberta Infant Motor Scales (AIMS at 4 and 12 months) and the Preschool Language Scales (at 12 months). Examiners were blinded to MDMA exposure. Maternal covariates measured to control confounding included psychological distress (Brief Symptom Inventory), addiction severity (Drug Abuse Screening Test), maternal IQ (two subscales of the Wechsler Abbreviated Scale of Intelligence), sociodemographic variables, postpartum drug use and the home caregiving environment (HOME inventory). Analyses compared MDMA versus non-MDMA groups and also used a three-group classification (heavier MDMA, lighter MDMA, non-MDMA). Heavier and lighter MDMA groups were defined by a median split of the total number of tablets averaged over pregnancy (heavier n = 13, lighter n = 15). Because many women reduced or ceased use across pregnancy, only one woman reported MDMA use in the third trimester. For longitudinal analyses of Bayley outcomes, mixed linear models with maximum likelihood estimation were employed. Potential covariates associated with both MDMA use and outcomes at p < 0.2 were evaluated and retained in models if significant at p < 0.10; gender effects were also examined.

Mothers averaged 29 years of age, were predominantly white (85%), largely partnered (82%), had some university education, were of middle socioeconomic status and had average intelligence. MDMA-using and non-MDMA-using women did not differ on most background variables, although MDMA users had fewer children. Polydrug use was common in both groups, primarily tobacco, cannabis and alcohol, and overall drug use decreased over the trimesters with cannabis most likely to persist. At birth there were no group differences in birthweight, prematurity, length or gestational age. However, MDMA-exposed infants were more likely to be male (71% vs 46%), with an odds ratio (OR) = 3.2, 95% confidence interval 1.2–8.2, p < 0.02 (an OR greater than 1 indicates higher odds of being male in the MDMA group). One MDMA-exposed child had Townes–Brocks syndrome; inclusion or exclusion of this case did not alter results. Neonatal neurobehavioral assessment showed no statistically significant group differences, though there were non-significant trends for MDMA-exposed infants to be more lethargic and less hypertonic. Motor outcomes diverged by 4 months. On the BRS, MDMA-exposed infants showed slower, more delayed movements at 4 months, and on the AIMS heavier-exposed infants scored lower: mean percentile 35.1 ± 24 for the heavier MDMA group versus 65.7 ± 23 for the lighter group and 45.9 ± 28 for nonexposed infants (p < 0.03). At 12 months motor deficits were more pronounced: the heavier MDMA group had a mean PDI of 76 ± 12 compared with 92.0 ± 16 and 99.8 ± 12 in the nonexposed and lighter groups respectively (F = 10.7, p < 0.002; the Bayley standard score average is 100). Examiner-rated motor quality on the BRS also differed, with heavier-exposed infants rated more poorly (F = 12.4, p < 0.001). Mental development differences were apparent only at 12 months: amount of prenatal MDMA exposure predicted lower MDI scores (β = 0.28, p < 0.012), though the decrement in the heavier group remained within the average range. When MDI and PDI were analysed longitudinally across 4, 12, 18 and 24 months using mixed models, no overall significant effect was found for MDI, but a significant main effect of MDMA exposure on motor outcomes persisted. By 24 months the heavier MDMA-exposed group had a lower modeled PDI (90.8, SE = 3.8) compared with lighter and nonexposed children combined (98.7, SE = 1.4). Language outcomes and several behavioural subscales (attention, arousal, orientation, emotional regulation) did not differ between groups at 4, 12, 18 or 24 months.

The investigators conclude that prenatal MDMA exposure was associated with an altered sex ratio and with persistent motor delays across the first 2 years of life, and that higher amounts of prenatal exposure were linked to lower mental and motor scores at 12 months. Motor deficits were detectable from 4 months and persisted through 24 months on standardised measures; mental outcome differences were limited to the 12-month assessment. Because most women ceased MDMA use after the first trimester, the findings are attributable primarily to first trimester exposure in this cohort. Potential mechanisms discussed by the authors include indirect effects mediated via increased maternal stress hormones (notably cortisol) associated with MDMA use and the drug’s known ability to cross the placenta, and direct effects on the developing serotonergic system, which plays a role in motor system development. The altered sex ratio is noted as consistent with other epidemiological observations linking fetal toxic exposures to shifts in sex ratios, though mechanisms remain unclear. Singer and colleagues identify strengths of the work as its prospective longitudinal design, blinded outcome assessment and control for polysubstance exposure and environmental confounders such as the home caregiving environment. They acknowledge key limitations: small sample size, reliance on self-reported drug use without biological biomarkers, and self-selection into the voluntary study that could introduce selection bias. The sample’s relative homogeneity and middle socioeconomic status reduced the presence of other common risk factors but may limit generalisability. The authors state that the motor delays observed could signal risk for later learning or school-age problems and therefore warrant long-term follow-up. They also recommend clinicians and public health practitioners caution pregnant women about potential developmental risks from MDMA, and call for research on newer recreational compounds (novel psychoactive substances) and on interactions between multiple drug exposures and maternal stress.

The authors conclude that prenatal MDMA exposure is associated with early fine and gross motor delays that may carry risk for later developmental problems, and they advocate for long-term follow-up to determine persistence and functional impact. Given the prevalence of MDMA use among women of childbearing age and misconceptions about its safety, they recommend warning pregnant women about potential adverse developmental effects, noting that negative outcomes may occur even when use stops prior to pregnancy. The authors also emphasise the need to study effects of newer recreational drugs and the combined influence of polysubstance use and maternal stress.