| Abstract
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 heroin users treated
with methadone report improvements in birth weight.
As a consequence, methadone treatment has become
the `gold standard' for the management of the
pregnant heroin user. However, not all studies
report significant birth weight increases associated
with methadone. We undertook a number of meta-analyses
on reduction in mean birth weight and incidence
of low birth weight to estimate more precisely
the effect of illicit heroin and methadone.
Introduction
Approximately 80-90% of women using intravenous
heroin are of reproductive age (Oleske, 1977;
NCADA--Australian National Drug Household Survey,
1993). Heroin readily crosses the placenta and
is associated with lower birth weight infants
(Vargas et al., 1975; Kandall et al., 1977; Whiting
et al., 1978; Little et al., 1990; Lam et al.
1992). Low birth weight is a known cause of neonatal
mortality (Harper, Solish & Purow, 1974; Kandall
et al., 1977; Chasnoff, Hatcher & Burns, 1982).
Many investigators claim that methadone treatment
for pregnant heroin users increases infant birth
weight significantly (Strauss et al., 1974; Kandall
et al., 1975; Stimmel & Adamsons, 1976; Ellwood
et al., 1987; Keith et al., 1989; Lam et al.,
1992).
Reported improvements in birth weight and neonatal
mortality associated with methadone treatment
have led authors to recommend it as the treatment
of choice for the pregnant woman using illicit
opiates (Strauss et al., 1974; Connaughton et
al., 1977; Ellwood et al., 1987; Lam et al., 1992).
However, despite the widely accepted belief that
treatment of pregnant heroin users with methadone
improves infant birth weight, a number of women
on methadone give birth to neonates with significantly
reduced birth weight (Kandall et al., 1975; Ellwood
et al., 1987; Lam et al., 1992). We combine the
relevant published data on the association between
maternal opiate use and infant birth weight in
a number of meta-analyses to estimate more precisely
the effect of illicit heroin, methadone and concurrent
use of methadone and heroin on mean birth weight
or prevalence of low birth weight.
Results showed mean reductions in birth weight associated
with heroin use: 489 g (95% CI 284-693 g), compared
with methadone: 279 g (229 328 g). Similarly, the
pooled relative risk estimate for low birth weight
for maternal heroin use was 4.61 (95% C] 2.78-7.65),
compared with 1.36 (0.83-2.22) for methadone. Analysis
of data on combined heroin and methadone use produced
a pooled mean reduction in birth weight of 557 g
(403-710g), with a pooled relative risk estimate
for low birth weight of 3.28 (2.47-4.39). Pooling
`any' methadone data, regardless of heroin use,
produced an estimated reduction in birth weight
of 395 g (311-478g) and a relative risk estimate
for low birth weight of 1.90 (1.29-2.81). Combining
all data in an `any' opiate use analysis also produced
a mean reduction in birth weight of 483 g (386-583g)
and a relative risk estimate for low birth weight
of 3.81 (2.57-5.65).
Pros and Cons of Methadone Use among Pregnant
Women
The desired goals of methadone maintenance during
pregnancy are to prevent abstinence syndrome with
associated risks to the fetus, reduce or eliminate
drug cravings, and block the euphoric effects
of narcotic drugs in order to reduce illicit drug
use. (Center for Substance Abuse…1995) methadone
maintenance provides a ‘steady state’
of opiate levels, thus reducing the risk of constant
withdrawal to the infant. Methadone also reduces
the use of street opiates, and thus decreases
the risk of ecological problems such as hepatitis,
HIV, other infections, prostitution, criminal
activity, and the general life disruption associated
with opiate dependence. The benefits of methadone
treatment of opioid dependence include decreases
in mortality and morbidity as well as improvement
in the quality of life issues.
During pregnancy, these benefits extend to the
developing fetus. By decreasing heroin use, methadone
decreases risks associated with needle use, drug-seeking
behaviors, fluctuating drug withdrawal, and exposure
to drugs of unknown concentration and impurities.
Left untreated these risks have been associated
with neonatal infection and even death. Furthermore,
methadone treatment may increase a patient’s
access to medical care, stable housing, and employment,
which further reduce the risks to the patient
and infant. Methadone treatment has the potential
long-term benefit for both mother and infant to
the extent that it can reduce the chances of a
return to illicit substance use in the postpartum
period.
Decreases in fetal respirations and movement have
been observed following maternal methadone use.
(Witt man, 1991)When methadone and other narcotics
are taken, maternal respirations and heart rate
may decrease. (Richardson, 1984) At times, decreased
birth weight and fetal death have occurred in
cases of combined methadone and other narcotic
use. (Hulse et al, 1997) Sweating, constipation,
and constricted pupils may persist with methadone
use. Clients may be observed for signs of intoxication
such as drowsiness, decreased respirations, bradycardia,
hypotension, and, in rare cases, coma.
If symptoms of intoxication are severe, the daily
methadone dose can be delayed until symptoms decrease.
(Kaye & Chasnoff, 1993)Just as abrupt withdrawal
from methadone during pregnancy may precipitate
preterm labor or fetal death, so can the acute
withdrawal caused by the use of Narcan or other
narcotic antagonists. Obstetrical complications
such as abruption, stillbirths, chorioamnionitis,
preterm labor, low birth weight, intrauterine
growth restriction, and postpartum hemorrhage
are more common in women using methadone. (Kaye
& Chasnoff, 1993)
It has been shown that methadone administration
results in increased birth weight when compared
to heroin use in pregnancy, though this could
be related to other factors such as improved prenatal
care.
(Woods, 1996) Methadone has been widely used in
pregnancy to reduce the risks of intravenous drug
use associated with heroin. In one comparison
among methadone maintained, heroin using, polysubstance
using and non-drug using women, those on methadone
gave birth to infants with smaller head circumferences
than controls. Women maintained on methadone also
received more prenatal care, had higher birth
weights and fewer complications than heroin using
mothers and their infants. Finally, methadone
maintained women had fewer distressed fetuses
than women using multiple substances did. (Stimmel
et al, 1983)
|