Greater use of prescribed opioids among women during pregnancy has probably contributed to the rise in neonatal abstinence syndrome, says an editorial in The BMJ.

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More American women are now using opioids during pregnancy.

Neonatal abstinence syndrome (NAS) is a serious medical condition that results when a newborn is exposed to addictive illegal or prescription drugs before birth.

A study published by the Centers for Disease Control and Prevention (CDC) describes it as "a constellation of physiologic and neurobehavioral signs exhibited by newborns exposed to addictive prescription or illicit drugs taken by a mother during pregnancy."

NAS occurs when a fetus has become physically dependent on opioids while in the womb, followed by abrupt discontinuation at birth due to separation from the mother.

In the US, it is estimated that 14-22% of pregnant women receive an opioid prescription while pregnant. The increase has been linked with a parallel rise in misuse, fatal overdoses and heroin use.

From 2000-2009, the incidence of NAS in the US increased from 1.20 to 3.39 per 1,000 live births, and from 2004-2013, the percentage of days spent in intensive care because of NAS rose from 0.6% to 4.0%.

Taking opioids close to the delivery day or for longer periods increases the risk, as does the use of drugs with short breakdown times. Opioid drugs with slow clearance rates, such as buprenorphine, cause less severe withdrawal than drugs with intermediate rates, such as methadone, or fast rates, such as morphine.

One study has reported that exposure to methadone before birth leads to a need for significantly more care for NAS than exposure to buprenorphine.

Dangers of opioid exposure

The effects of opioid exposure on the fetal brain are unknown, but central nervous system (CNS) birth defects have been observed in rodent studies.

Studies in humans have suggested that opioid use during pregnancy can lead to neural tube defects and other birth defects.

It is possible that opioid exposure could also disrupt attachment between mother and baby. Cognitive impairments have been reported in children and young people born to women who misused opioids during pregnancy, although this could be influenced by the use of other drugs or lifestyle factors.

Nora Volkow, director of the National Institute on Drug Abuse at the National Institutes of Health in Bethesda, MD, and author of the editorial, believes that the growing incidence of NAS is related to the higher rates at which opioids are prescribed to women during pregnancy.

She argues:

"The steep increase in the number of opioid prescriptions dispensed in the US has been associated with a parallel rise in their misuse, fatal overdoses and heroin use. More recently, attention has been focused on the large increase in the number of infants born with neonatal abstinence syndrome."

Volkow recommends prescribing opioids for pregnant women only in cases of severe pain that cannot be controlled with less harmful treatments and for as short a time as possible.

If long-term use is unavoidable, such as for women receiving treatment for heroin addiction, Volkow calls for careful assessment and monitoring to reduce the risk of overdose, misuse and NAS.

Medical News Today recently reported that doctors are continuing to prescribe opioids to patients, even after they experience an overdose.