Children whose mothers smoked during pregnancy may have a tougher time controlling their asthma than other kids do, a new study suggests.

The findings, from a study of nearly 2,500 U.S. kids, add to evidence that prenatal smoking may affect children’s future lung health.

There are already plenty of reasons for women to quit smoking during, and ideally before, pregnancy, said lead researcher Sam Oh, of the University of California San Francisco.

This study offers more motivation for women, and for doctors to ask moms and expectant moms about smoking, Oh said in an interview.

“Pregnancy is a great opportunity for smoking cessation,” he said.

Smoking during pregnancy is linked to increased risks of miscarriage, low birth weight, certain birth defects and other pregnancy complications.

As for asthma, many studies have found that secondhand smoke may worsen children’s asthma symptoms, or possibly raise their risk of developing the lung disease in the first place. The same risks have been linked to moms’ prenatal smoking.

But, Oh’s team says, it has not been clear how much of an impact prenatal smoking might have on kids’ asthma symptoms later in life, independent of any current exposure to secondhand smoke.

HIGHER RISK AMONG POOR MINORITIES

For their study, the researchers focused on 2,481 black and Hispanic kids between the ages of 8 and 17 who all had asthma and were mostly from low-income families.

In the U.S., poor, minority children are at particular risk of asthma. About 16 percent of low-income black children have asthma, versus the national prevalence of 9 percent, according to the U.S. Centers for Disease Control and Prevention.

In this study, almost 19 percent of African-American moms smoked at some point during pregnancy, as did 5.5 percent of Hispanic moms.

Overall, their kids were at greater risk of poor asthma control later in life, even when childhood secondhand-smoke exposure was taken into account - as well as other factors like a child’s age and asthma medication use.

About 30 percent of Hispanic kids and 38 percent of black kids had poorly controlled asthma symptoms - and the risk was 50 percent for those exposed to smoking in the womb, versus unexposed kids.

“There are measurable effects even years down the road,” Oh said.

The findings do not, however, prove that prenatal smoking, itself, causes more-severe asthma symptoms later in life. They can only point to a correlation.

But there is lab research, in animals and human cells, suggesting there could be a direct effect, Oh pointed out.

Fetal exposure to tobacco smoke may, for example, impair early lung development, or have lasting effects on the activity of certain genes.

The bottom line, according to Oh, is that there is already a host of reasons for pregnant women to quit smoking for good, and this may be one more.

“This study provides more impetus for healthcare providers to ask about smoking at each visit,” he said.

Some pregnant women may be able to quit with behavioral counseling. In some cases, a doctor may prescribe nicotine replacement therapy or other medication.

SOURCE: Journal of Allergy and Clinical Immunology, online April 30, 2012