eat dirt, as we will later suggest our kids should do (although some pregnant women have an urge to do so—see Care for a Spoonful of Soil? on page 51).
Despite best efforts to avoid them, infections during pregnancy are quite common, with urinary tract infections (UTIs) and bacterial vaginoses both affecting about 1 in 6 pregnant women in the United States and about 1 in 10 pregnant women in Canada. Other commonly diagnosed infections during pregnancy are respiratory tract and skin infections. Fortunately, several antibiotic medications are safe to use during pregnancy, but they’re being prescribed to a lot of women—very likely more than necessary. The most recent National Birth Defects Prevention Study in the US, which has been collecting data since 1997, showed that almost 30 percent of women receive at least one course of antibiotics during pregnancy. A population-based study (a term given to studies involving a very large number of people) in the UK showed that the same is true for British women, while 42 percent of French and 27 percent of German women take antibiotics while pregnant. There’s no debate about the immense change that an antibiotic brings to the microbiota. After a course of antibiotics, the overall diversity of the microbiota is substantially reduced. Its effect can be compared to what happens when a lush rain forest gets chopped down, and only a few dominant species make a comeback. Fortunately, the adult microbiota is fairly stable, and after finishing a course of antibiotics, in a nonpregnant woman this microbial forest usually returns to normal. The concern during pregnancy is that the microbiota fluctuates considerably, which is a characteristic of unstable ecosystems that are more susceptible to abrupt changes and permanent damage. When expectant women take antibiotics, especially in the last two trimesters, their microbiota takes a major hit, and according to new research, so does the microbiota of their babies. What becomes even more concerning is that antibiotic use during pregnancy is now being associated with certain diseases seen later in children.
A study of more than seven hundred pregnant women from New York showed that children born to those who received antibiotics in their second and third trimesters had an 85 percent higher risk of childhood obesity by age seven. These results are very significant because they were obtained after correcting for other confounding variables of obesity, such as the weight of the mother, the birth weight of the child, and whether or not the infant was breastfed. All of these factors were previously shown to be associated with the risk of obesity, so it’s important (for this and any other similar study) to remove these variables from the analysis. These findings are quite new (published in 2014) and they still need to be replicated, but if more studies show a similar trend, it suggests that childhood obesity may have roots in the very early stages of human development, and that antibiotic use during pregnancy has significantly more risk than is currently assumed in medical practice.
Antibiotic use during pregnancy has also been associated with asthma, eczema, and hay fever in infants. Two large studies from Finland, a country that has experienced a twelve-fold increase in asthma rates since the 1960s, showed that using antibiotics during pregnancy is a significant risk factor for early asthma in babies. Other epidemiological studies have found similar associations between antibiotic use during pregnancy and inflammatory bowel disease (IBD) and/or diabetes, each of which is discussed in detail in forthcoming chapters. What’s very peculiar is that these diseases share common risk factors. They are all immune disorders that have become increasingly common in the past few decades, and they usually occur in individuals with certain known genetic predispositions. Recent research on humans and animals show that the risk factors associated with these diseases also involve the early microbiota. How early? According to the studies, these changes begin before we’re born, through mechanisms that are just beginning to be understood.
As frequently occurs in science, the insights on the mechanisms that explain a disease come from animal experiments. In this case, neonatology researchers from the Children’s Hospital of Philadelphia showed that baby mice born to mothers that received antibiotics during pregnancy had a reduced immunological response. Similarly, a separate study showed that mice predisposed to diabetes and born to females that were given antibiotics had persistent alterations in their immune cells. These same mice developed diabetes a lot sooner than mice born to females that did not receive antibiotics. While a lot more research is still needed to fully understand all of this, it’s becoming evident that complex interactions between microbes, the immune system, and other aspects of human metabolism, occurring as early as in utero (before birth), influence the risk of disease later in life.
Getting Smart About Antibiotics
In light of all these findings it is crucial to understand that using antibiotics should not be discouraged when they’re really needed, but the overuse or abuse of antibiotics should be prevented. So, when are antibiotics necessary during pregnancy? The answer is simple: antibiotics should be taken for serious bacterial infections, and only bacterial infections. However, this can be hard to put into practice, especially during pregnancy, when doctors want to prevent any possible complications that may arise from an infection. Because of this, many health providers are too quick to prescribe antibiotics, as a safety precaution, to expectant mothers for ailments that don’t require antibiotics, like the flu. The flu is a viral disease that causes symptoms that many people confuse for a bacterial respiratory infection. Its onset is very sudden and people feel awful for about a week, until they start getting better. It’s not hard to imagine a pregnant woman showing up at a doctor’s office almost begging to get a prescription that will make her feel a little bit better. However, antibiotics should not be used for the flu, regardless of how bad a patient feels.
There are exceptions to this, though; the flu can lead to secondary bacterial infections that do require antibiotic treatment. This usually manifests a little bit differently: you feel truly awful, and after a week or so, you start to get better, but then you start feeling worse, with coughing and chest congestion, which can lead to pneumonia. This is the classic example of a secondary bacterial infection following the flu, which should be treated with antibiotics.
However, the key concept here is to prevent infections from occurring in the first place if possible. As such, it is currently recommended that pregnant women get a flu shot. Fortunately we have an effective vaccine that is completely safe to use during pregnancy, which significantly decreases the chances of getting the flu and a secondary respiratory bacterial infection during flu season.
Despite the precautions you can take, infections do happen during pregnancy and antibiotics are prescribed. So what then? Based on the current research, it seems that the period at which antibiotics are taken is important, with microbial changes in the later stages of pregnancy being the most influential. If antibiotics must be used in the second and especially the third trimester, one should start or continue microbial supplementation with probiotics and a diet rich in fiber and vegetables. It’s important to choose a probiotic that contains several species of Lactobacillus and Bifidobacterium, both known to be important early members of an infant’s microbiota. As with any supplement or medication taken during pregnancy, we recommend discussing this with your health care provider.
Heading Off Group B Strep
During the births of her first two children, Neve had been given antibiotics, an increasingly common occurrence nowadays, with 1 in 3 women receiving antibiotics during labor. Neve knew how frequent antibiotic use is during delivery because she had tested positive for a type of bacteria known as Group B streptococcus, or GBS for her first two births. (Other very common circumstances that require antibiotics during labor are scheduled C-sections, which will be discussed extensively in chapter 4.) In many countries, all women between 35–37 weeks of gestation get tested for GBS. These bacteria commonly reside in 15–40 percent of all pregnant women, yet they rarely cause any symptoms. However, between 40–70 percent of GBS-positive women will pass it on to their babies during natural birth, and a small but very significant number of babies (1–2 percent) will develop a GBS infection (for further discussion of GBS infections, see chapter 4). Fortunately, if a pregnant woman who tests positive for GBS is treated with antibiotics during labor, the risk of her baby developing a GBS infection is reduced by 80 percent, making GBS prevention a pertinent use of antibiotics.