NIH Record - National Institutes of Health

Enabling Data-Driven Decisions

How Asthma, Pollution Affect Health of Pregnancy, Newborns

Dr. Pauline Mendola
Dr. Pauline Mendola

​If you’re pregnant and have asthma, you or your newborn may have complications during delivery. Either of you might have residual health problems afterwards, or you both may be fine. Until recently there wasn’t a lot of information to help you and your medical team make a plan. Over the past decade or so at NIH—and over the course of her career—Dr. Pauline Mendola, senior investigator in NICHD’s Epidemiology Branch, has sought to change that. She gave the year’s first NIH Director’s Seminar Series lecture, “Asthma and Pregnancy: Adverse Outcomes and Susceptibility to Air Pollution,” on Jan. 10 in Wilson Hall.

“Maternal asthma is really important in terms of population health,” she said. About 10 percent of pregnancies in the United States are complicated by asthma, which makes the lung disorder the most common chronic disease in pregnancy.

The clinical course of asthma in pregnant women seems to follow a widely variable “third third third rule,” Mendola explained. “About a third of women are supposed to get better, some get worse, some stay the same…Because there is very little in the way of empirical data, clinicians by and large are left to watch people and hope things go well.” 

Add air pollution to the mix, Mendola said, and documented data on pregnancy health effects become even more scarce.

In general, she said, both air pollution and asthma independently increase obstetric and neonatal risks of poor outcome. Each condition can also lead to long-term effects for both mother and offspring. Air pollution can make asthma worse, Mendola pointed out, but there’s very little data on the potential joint effects of asthma and air pollution.

“We don’t think about it, but breathing is a ubiquitous exposure that we can’t really do a lot about,” she said. “We have to breathe the air that’s there.”

The air that’s there contains several potentially harmful compounds and many of them are tiny enough to penetrate the body’s upper airways and infiltrate deep into our general circulation, Mendola explained.

All day, we’re all breathing in various combinations of what sounds like chemical alphabet soup. Our air contains such particles as PM10 and PM2.5, gases like carbon monoxide and sulfur dioxide and such air toxics as PAHs, or polycyclic aromatic hydrocarbons, and VOCs, or volatile organic compounds.

With previous research posts at the Environmental Protection Agency and CDC’s National Center for Health Statistics, Mendola has studied the intersection between reproductive and environmental epidemiology for more than 20 years. The current increase in lung disease does not surprise her. 

“The reason we’re seeing so much asthma now in the obstetric population is because we had the childhood epidemic of asthma in the 1980s and 1990s and those people are having babies now,” she said.

She discussed data from several significant studies, citing three NICHD-led efforts in particular: the Consortium on Safe Labor (CSL), a nationwide obstetric cohort conducted 2002-2008; the Air Quality and Reproductive Health (AQRH) Study, which Mendola designed using hourly U.S. weather and emissions grids; and Breathe-Wellbeing Environment, Lifestyle and Lung Function (B-WELL-Mom Study), a clinical study.

CSL collected information from electronic hospital admissions records on more than 223,300 singleton deliveries. Over 17,000 of those deliveries were complicated by maternal asthma.

“We found that mothers with asthma have really high rates of obstetric complications,” she said. These include preeclampsia, gestational diabetes, breech presentation, preterm birth and pulmonary embolism. “For nearly every complication we studied, asthmatic women had higher risk.”

In addition, newborns of mothers with asthma also showed increased health risks such as being small for gestational age, NICU (neonatal intensive care unit) admission and jaundice. 

“Interestingly, we find that newborns of mothers with asthma also have higher rates of upper respiratory conditions,” continued Mendola. “So their lung function even as neonates is poorer than babies born to moms who don’t have asthma.”

Mendola speaking with Owens
Mendola chats with Dr. Roland Owens of NIH’s Office of Intramural Research.

Photo:  Credit Chia-Chi Charlie Chang

Examining the effects of certain pollutants on pregnancy complications such as preterm birth and preeclampsia, the AQRH study found significant differences in risks between women with asthma and those without at the same exposure levels.

“Even when the VOC exposure increased preeclampsia risks for non-asthmatic moms, the risk was twice as high for the asthmatic moms,” Mendola said. 

Looking at neonatal respiratory outcomes and air pollution, there was no difference in risk between asthmatic and non-asthmatic moms; all showed about the same amount of risk from air exposure.

Finally, Mendola described the B-WELL-Mom study, which recently completed data collection. 

As a clinical study, B-WELL-Mom has several advantages over CSL and AQRH. B-WELL-Mom offers detailed biologic assessments, follows patients over time and looks at whether and how asthma is being controlled and how much symptoms bother the participants. A GPS component can give more detail about the various environments where participants travel over the course of their pregnancies.

B-WELL-Mom also looks at underlying factors that may account for changes in asthma control during pregnancy, such as what may be happening with immune system T cells. 

“There are a few studies that suggest the better your asthma control is during pregnancy, the better your outcomes will be,” Mendola said. “So, good asthma control really mitigates poor outcomes.”

B-WELL-Mom’s primary aim is to identify factors that predict asthma control variability during pregnancy, thereby providing caregivers with data they can use in treatment situations.

“Your immune response to pregnancy—does that tell us something about that phenotype of asthma that may be useful for other therapeutics?” Mendola asked. “[Asthma] is not a trivial disease and has a substantial impact on lifelong morbidity and mortality…These studies also teach us something about the immunology of pregnancy.”

About 5 percent of pregnant asthmatics will be hospitalized with an asthma crisis, she pointed out. Her team wants ways to identify those patients in advance of trouble and perhaps provide clinical interventions.

“Right now, clinicians are seeing 10 percent of the obstetric population with asthma and there is very little data to help them predict who’s going to get worse and who’s going to get better,” Mendola concluded.  

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