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Published: Tuesday, March 22, 2011 - 12:10

According to an ongoing, population-based study conducted by the Centers for Disease Control and Prevention (CDC)codeine in pregnancy, women receiving opioid analgesics (pain-killers) such as codeine and dihydrocodeine in early pregnancy had a 2- to 3-fold increased risk of delivering infants with congenital heart defects as well as other major congenital anomalies including gastroschisis and spina bifida. The identified congenital heart defects are conoventricular septal defects, atrioventricular septal defects (‘hole in the heart’) and  the very serious and potentially lethal hypoplastic left heart syndrome. The study has just been published online in the American Journal of Obstetrics and Gynecology

Commonly used opioid pain-killers include codeine, hydrocodone, meperidine, oxycodone, propoxyphene, morphine, tramadol, methadone, hydromorphone, fentanyl, or pentazocine. All these are available in combined forms and an array of brand names, the most common being Co-codamol, Co-dydramol, Kapake® Tylex®, Solpadol® and Codipar®.

"It's important to acknowledge that although there is an increased risk for some types of major birth defects from an exposure to opioid analgesics, that absolute risk for any individual woman is relatively modest," principal investigator Cheryl S. Broussard, PhD, from the CDC's National Center on Birth Defects and Developmental Disabilities, said in a news release.

"However, with very serious and life-threatening birth defects like hypoplastic left heart syndrome, the prevention of even a small number of cases is very important," she said.

According to the study authors, previous research has shown that opioid analgesic use and abuse have been increasing in recent years but their effects on the developing fetus are poorly understood. Studies that looked at their potential effects have been plagued by insufficient sample sizes and inconsistent results.

Major birth defects affect about 3% of the all live births. They are one of the leading causes of neonatal and infant deaths. Congenital heart defects are the most common type of birth defect, affecting nearly 1% of all births, and are the main contributor to infant mortality attributable to birth defects.

Hitherto regarded as safe

"Despite evidence of adverse fetal effects with maternal codeine use and the paucity of data on the effects of maternal use of other opioids, such treatment is often assumed to be safe during pregnancy," the study authors note.

To examine whether maternal therapeutic use of opioid painkillers in early pregnancy is associated with birth defects, the investigators analyzed data from the National Birth Defects Prevention Study, an ongoing, population-based, case-control study for infants born October 1, 1997, through December 31, 2005, in 10 states (in the United States).

This study focuses on infants with birth defects of unknown causes, so those with recognized chromosomal abnormalities or single-gene disorders are excluded.

Mothers were interviewed between 6 weeks and 2 years after the estimated date of delivery and queried about various maternal health factors, pregnancy history information, dietary and drug exposures, and socio-demographic characteristics.

Exposures were assessed for the period from 3 months before conception through the end of pregnancy.

The researchers defined opioid exposure as maternal report of one or more opioids taken for therapeutic reasons. These included codeine, hydrocodone, meperidine, oxycodone, propoxyphene, morphine, tramadol, methadone, hydromorphone, fentanyl, or pentazocine. The exposure window of interest was the period from 1 month before to 3 months after conception.

The investigators found that therapeutic opioid use was reported by 2.6% of 17,449 case mothers and 2.0% of 6701 control mothers. The most commonly prescribed opioids included codeine (34.5%), hydrocodone (34.5%), oxycodone (14.4%), and meperidine (12.9%).

Codeine and Hydrocodone

Codeine and hydrocodone exposure were slightly more common among cases, and oxycodone and meperidine were slightly more common among controls.

Codeine and hydrocodone accounted for most of the statistically significant findings, the study authors note, but these drugs were also the most commonly used, representing 69% of all reported exposures.

It's possible, the study authors say, that some of the findings may be due to chance. "Our results should be treated with caution and deserve further investigation," they write.

They did not have information on medication dose so were unable to assess dose-response relationships. In addition, illicit drug use was not assessed.

"It is critical that health care providers weigh the benefits of these medications along with their potential risks when discussing analgesic treatment options with patients who are or may become pregnant, including reproductive-aged women who are not planning a pregnancy but might be at risk of an unintended pregnancy," the study authors write.

Source abstract:

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Opioid painkillers may increase risk of birth defects

By Dr Joe Kabyemela, MD