Most women presenting with opioid dependence are of child-bearing age with chaotic drug use predisposes to amenorrhoea. The initiation of opioid substitution therapy (OST) facilitates stability and reinstatement of regular menstrual cycles and thus OST is a risk factor for unplanned pregnancy. Contraception needs to be discussed with all female patients of child bearing age who present to OST treatment services.
Substance use disorder in pregnancy mandates referral to a specialist services with best practice including involvement in a multidisciplinary drug and alcohol antenatal clinic. This multidisciplinary team should include: midwives, Obstetricians, Paediatricians, social workers and Addiction Medicine specialists.
Counselling needs to be provided regarding the risks and benefits of OST during pregnancy and lactation. There is a significant risk of miscarriage if doses of OST missed/opioid withdrawal occurs. Pregnant patients may be reluctant to engage with antenatal services or OST treatment programs because of chaotic lifestyles, stigma or concerns about child protective services and removal of their child from them post birth. By focussing on the health of the baby this may promote engagement with treatment services.
Suboxone, Subutex and Methadone are all Category C drugs in pregnancy. However inadequately treated opioid use disorder is a significant risk to the viability of the pregnancy. Opioid withdrawal in the first trimester can cause uterine contractions and does increase the risk of miscarriage in the first trimester and opioid withdrawal in the third trimester increases the risk of intrauterine growth restriction as well as risk of premature labour.
Another concern about OST in pregnancy is adequately dosing the pregnant woman. The half life of Methadone is reduced in pregnancy from 22-24 hours in non-pregnant women to 8.1 hours in pregnant women. Methadone metabolism is accelerated due to increased CYP3A4 expression by liver, intestine, and placenta and methadone clearance increases with advancing gestational age. As a result of this higher doses and split dosing of Methadone may be required.
An optimal dose of methadone remains controversial with doses of 80-120mg per day not inappropriate. Twice or thrice daily dosing can result in more sustained plasma levels, fewer withdrawal symptoms, and less illicit drug use and less suppression of foetal movement and breathing.
Thus in summary it is important to adequately treat women who are pregnant with opioid use disorder to prevent harms to both the woman and foetus.