THE RELATIONSHIP BETWEEN MATERNAL USE OF HEROIN AND METHADONE AND INFANT BIRTH-WEIGHT

Aims/design. Reduction in mean birth weight and increased incidence of low birth weight are both associated with exposure to illicit heroin in pregnancy. Many studies examining neonatal outcomes in pregnant her oin users treated with methadone report improvements in birth weight. As a consequence, methadone treatment has become the 'gold standard' f or the management of the pregnant heroin user. However, not all studie s report significant birth weight increases associated with methadone. We undertook a number of meta-analyses on reduction in mean birth wei ght and incidence of low birth weight to estimate more precisely the e ffect of illicit heroin and methadone. Findings. Results showed mean r eductions in birth weight associated with heroin use: 489 g (95% CI 28 4-693 g), compared with methadone: 279 g (229-328 g). Similarly, the p ooled relative risk estimate for low birth weight for maternal heroin we was 4.61 (95% CI 2.78-7.65), compared with 1.36 (0.83-2.22) for met hadone. Analysis of data on combined heroin and methadone we produced a pooled mean reduction in birth weight of 557g (403-710 g), with a po oled relative risk estimate for low birth weight of 3.28 (2.47-4.39). Pooling 'any' methadone data, regardless of heroin use, produced an es timated reduction in birth weight of 395 g (311-478 g) and a relative risk estimate for low birth weight of 1.90 (1.29-2.81). Combining an d ata in an 'any' opiate we analysis also produced a mean reduction in b irth weight of 483 g (386-583 g) and a relative risk estimate for low birth weight of 3.81 (2.57-5.65). Conclusions. The current findings su ggest that heroin use while receiving methadone may counteract the bir th weight advantage gained from methadone alone. Whether this is due t o fetal exposure to heroin plus methadone, to reduced antenatal care, other behavioural and environmental factors associated with concurrent use of heroin and methadone or a combination of these is unclear. Nev ertheless, these results challenge the current belief that the pregnan t user is always better off receiving methadone than not, and suggests that methadone may not be the appropriate treatment for the pregnant women who continue to use illicit heroin.