The potential dangers of illegal drug use are never far from the media spotlight, and drug use during pregnancy may be associated with particular health problems both for the Mother and baby. Drug use during pregnancy has been linked with a number of negative outcomes, for example, cocaine use has been linked with an increased risk of placental abruption, while opiate use has been linked with neonatal abstinence syndrome and low birth weight. However, much of this research has failed to control for cigarette smoking status, which in itself has been associated with an increased risk of placental abruption, poor fetal growth, and late intrauterine death. Given that the majority of illegal drug users smoke, it is important to determine which maternal and prenatal health issues are specifically associated with illegal drug use.

Earlier this year, the Acta Obstetricia et Gynecologica Scandinavica published a retrospective cohort study, aimed at determining specific maternal and prenatal health issues associated with illegal drug use while controlling for cigarette smoking. They found that illegal drug use was associated with several serious health implications beyond that of smoking cigarettes.

Methods

Black and colleagues accessed the Aberdeen Maternity and Neonatal databank to identify women who had smoked during pregnancy, and contacted specialist ante-natal clinics in the same area of Scotland to identify women who had taken illegal drugs during pregnancy. 561 women were identified as illegal drugs users while pregnant. Of this group, 459 (82%) were prescribed methadone, 433 (77%) used heroin, 387 (69%) used benzodiazepines, and 190 (34%) used cocaine. The majority (85.6%) used more than one illegal drug and smoked cigarettes (96%). This drug using group was compared to 4,463 women who had reported smoking cigarettes during pregnancy.

Maternal baseline data included age, body mass index, and parity (childbirth history).

Primary outcome measures were:

• Low birth weight (birthweight less than 2,500g) & Standardised birthweight score (SBS takes into account gestation, fetal sex, and maternal parity)
• Neonatal unit admission
• Perinatal death (stillbirth and fetal loss after 20 weeks gestation, and neonatal death up to 7 days of life)

Other outcome measures were:

• Gestational hypertension (diastolic pressure >90 mm Hg on two occasions at least four hours apart, or a single reading of >110 mm Hg; from 20 weeks gestation onwards in a previously normotensive woman)
• Pre-eclampsia (gestational hypertension plus ≥1 episode of proteinuria of 0.3 g/24 hrs)
• Antepartum haemorrhage (hospital attendance with vaginal bleeding beyond 24 weeks gestation)
• Deep vein thrombosis (a radiological diagnosis of venous thrombus made during pregnancy)
• Assisted delivery
• Caesarean section
• Preterm delivery (delivered <37 completed weeks gestation)
• Induction of labour (artificial rupture of membranes or use of prostaglandins to initiate labour)
• Oxytocin augmentation (intrapartum oxytocin use after spontaneous onset of labour)
• Manual removal of placenta
• Postpartum haemorrhage (estimated blood loss >500ml)

Results

In terms of baseline maternal differences, illegal drugs users were less likely to be aged under 20 or over 35 years, or to be primigravid (pregnant for the first time). In addition, illegal drug users were 50% more likely to be underweight than women who smoked cigarettes only.

The authors calculated adjusted odds ratio (AOR) with 95% confidence intervals (CI) to identify associations between illegal drug use during pregnancy and maternal and neonatal outcomes, and to determine whether these associations were significantly different from those between cigarette smoking and outcomes.

Babies who were exposed to illegal drugs were more likely to

• Have a low birthweight [AOR 1.9, CI 1.4-2.6]
• Be admitted to the neonatal unit [AOR 16.1, CI 12.9-20.1]

Women who had used illegal drugs during pregnancy were more likely to have

• Antepartum haemorrhage [AOR 1.6, CI 1.2-2.1]
• Deep vein thrombosis [AOR 21.1, CI 8.8-50.8]
• A preterm delivery at any gestation [AOR 1.6, CI 1.3-2.1].

However, women who had used illegal drugs during pregnancy were less likely to develop gestational hypertension than those who smoked cigarettes [AOR 0.3, CI 0.2-0.4].

Conclusions

The authors conclude that there is an:

Increased risk of antepartum haemorrhage, preterm delivery, low birth weight infants and admission of infants to the neonatal unit in pregnancies affected by illegal drug use, over and above that which can be explained by the effects of smoking cigarettes. This study also identified a lower prevalence of gestational hypertension in women using illegal drugs.

The authors suggest that the reduced risk of gestational hypertension in the women using illegal drugs may be due to lower BMI and the fact that many illegal drugs have a direct hypotensive effect.

The authors also suggest that although smoking is associated with a low BMI, the finding that women using illegal drugs still had a significantly lower BMI:

May be a reflection of these women investing more time and energy on satisfying their addiction than ensuring an adequate dietary intake.

Strengths and limitations

It is important to correctly identifying which behaviours are associated with specific health problems, and to help patients improve their own health as well as that of their children. This is a fairly large cohort study that has identified health problems which are specifically associated with illegal drug use during pregnancy.

However, given that this is a retrospective study, there are limitations. For example, it is possible that some of the ‘control’ cigarette smokers had also taken illegal drugs during pregnancy but were not known to the specialist ante-natal clinics. In addition, smoking behaviours (e.g. number of cigarettes smoked per day) were not known; it is possible that the illegal drug users also smoked significantly more cigarettes. Although the study suggested significant effects of BMI, these must be taken with caution as 24% of this data was missing for the illegal drug users.

To determine whether these findings are valid, future research needs to conduct a prospective study in which a greater level of information can be obtained in terms of drug, alcohol, and smoking use during pregnancy while taking into account potentially confounding factors such as social deprivation and diet.

Links

Acta Obstet Gynecol Scand. 2013 Jan;92(1):47-52. doi: 10.1111/j.1600-0412.2012.01519.x. Outcomes of pregnancy in women using illegal drugs and in women who smoke cigarettes. Black M, Bhattacharya S, Fairley T, Campbell DM, Shetty A. [PubMed abstract]

Kuczkowski. The effects of drug abuse on pregnancy. Current Opinion in Obstetrics & Gynecology 2007 Dec;19(6):578-85. [PubMed abstract]

Pregnancy and complex social factors: A model for service provision for pregnant women with complex social factors (PDF). NICE CG110, 2010.

Grimes and Schulz. Making Sense of Odds and Odds Ratios (PDF). Obstetrics & Gynecology 2008 Feb; 111(2 Pt 1): 423-6. doi: 10.1097/01.AOG.0000297304.32187.5d.