April 5th, 2010 
Regular exercise during pregnancy doesn’t change a mother’s body weight but does lead to a small reduction in the baby’s weight, a new study shows.
The findings are important because larger birth size is associated with higher risk for childhood obesity.
In a randomized trial of 84 first-time mothers, participants were assigned to either an exercise or a control group. Exercisers rode stationary bikes for 40 minutes, five days a week, while the other women just maintained their regular activity. The women began exercising in the 20th week of pregnancy and continued until at least week 36.
The exercise didn’t make any difference in the mother’s weight compared to mothers who weren’t exercising. But among mothers who didn’t exercise, their babies were an average of five ounces heavier than babies born to women who exercised during pregnancy. There also was no difference in the average length of the babies, according to the study published in the Journal of Clinical Endocrinology and Metabolism.
The study shows that moderate, regular aerobic exercise can have a meaningful effect on a baby’s birth weight without putting the pregnancy or child at risk.
Related
- Exercise May Lower Risk of Having Heavy Babies
For women having their first child, regular exercise during pregnancy can lower the chances of having an overweight baby, researchers say.
Working out at least three times per week reduced the odds of delivering a newborn with excessive birth weight — above 4,000 grams (8.8 pounds) — by about a quarter, Katrine Mari Owe, MS, of the Norwegian School of Sport Sciences in Oslo, and colleagues reported in the October issue of Obstetrics & Gynecology.
The associations with exercise weren’t as strong for women who have had children previously, who were more likely than first time moms to have an overweight baby.
Research has shown that regular exercise is an important part of a healthy pregnancy. But studies of the association between physical activity and mean birth weight have been inconsistent.
To clarify the issue, the researchers analyzed data from the Norwegian Mother and Child Cohort Study of 36,869 normal singleton pregnancies. They collected data on newborn birth weight from the Medical Birth Registry of Norway.
In their study, mean birth weight was 3,682 grams (8.1 pounds), and 11% of newborns were classified as being in the 90th percentile or more of birth weight, categorizing them as “excessive.”
For veteran moms, the researchers found an inverse association between regular exercise — at least three times per week — and excessive newborn birth weight.
Risk fell by 28% for those who were exercising at week 17 of their pregnancy (95% CI 0.56 to 0.93) and by 23% for those who worked out at week 30 (95% CI 0.61 to 0.96).
The risk of having an overweight baby trended downward with exercise among veteran moms, but the difference did not reach significance, the researchers said.
There was a decreased risk for excessive birth weight among veteran moms who used dance as a form of exercise in week 17 of their pregnancy (OR 0.75, 95% CI 0.63 to 0.90).
The association was even stronger for week 30 (OR 0.69, 95% CI 0.53 to 0.88), and at that time point, low-impact aerobics was associated with decreased risk as well (OR 0.68, 95% CI 0.47 to 0.97).
On the other hand, veteran moms women were more likely to have heavy babies if they trained in fitness centers during week 17 of their pregnancy (OR 1.16, 95% CI 1.00 to 1.35) or if they swam during week 30 (OR 1.16, 95% CI 1.04 to 1.30).
For first time moms, walking decreased risk at weeks 17 and 30 (OR 0.86, 95% CI 0.75 to 0.99 and OR 0.84, 95% CI 0.73 to 0.96), as did running at week 17 (OR 0.63, 95% CI 0.45 to 0.89).
One possible explanation for exercise lowering risk of excessive birth weight among newborns is the effect of aerobic exercise on glucose tolerance, the researchers said.
Research has shown that moderate physical activity during pregnancy can lower glucose levels in both disease-free women and those who have gestational diabetes.
The study also found that exercising for three months prior to pregnancy didn’t have any effect on the odds of having heavier babies for either first time moms or veteran moms, the researchers said.
The women who elected to participate had a slightly different age distribution, lower parity, were less likely to smoke and less likely to have a preterm birth.
- E-ZPass Reduces Preemies, Low Birth Weight
Not only has E-ZPass shortened commutes, it might be making babies healthier too.
Mothers who lived near a toll plaza with an E-ZPass had fewer instances of premature births and low birth-weight babies, according to a new study.
Babies born near toll plazas were more likely to be healthy after E-ZPass lanes were installed and helped reduce traffic congestion.
Janet Currie and Reed Walker of Columbia University’s Department of Economics compared mothers that lived within three kilometers of a toll plaza with those that lived within three kilometers of a major highway (but not near a toll plaza) in New Jersey and Pennsylvania.
By reducing congestion and emissions through the E-ZPass system, premature births dropped 10.8% and instances of low birth weight declined 11.8% for mothers within two kilometers of the toll plaza.
For those who lived three kilometers from the plaza, prematurity and low birth weight fell 7.3% and 8.4%, respectively.
The conclusions are of particular interest, the researchers say, because low birth weight has been linked to health problems in the future and lower educational attainment. But it also shows the effects of a system like E-ZPass that has an inherent value to consumers – reduced travel time – as well as peripheral benefits, such as reduced emissions and health benefits.
Previous estimates showed that E-ZPass, an electronic toll system that reads a tag mounted on the windshield without forcing the vehicle to stop, reduced traffic congestion by more than 85% in some plazas within its first year. Other studies revealed it may have cut harmful emissions by up to 50%.
But the E-ZPass study took that research a step further by trying to determine traffic congestion’s health effects.
The researchers used Vital Statistics Natality records, which cover all births in a state, from Pennsylvania for 1997 to 2002 and for New Jersey from 1994 to 2003. They then compared the change in the number of premature and low birth weight babies born to mothers near toll plazas with those born to mothers who were not near toll plazas before and after the E-ZPass.
With roughly 26% of homes located near congested areas, Currie and Walker concluded that “…nationwide reductions in prenatal exposure to traffic congestion could reduce preterm births by as many as 10,800 annually, a reduction that can be valued at $557 million per year,” the study states. “Since we have focused on only one of the possible health effects of traffic congestion, albeit an important one, the total health benefits of reducing pollution due to traffic congestion are likely to be much greater.”
- Birth defects in babies linked to mother’s job
Women working as scientists and pharmacists run a greater risk of having babies with birth defects as compared to women in other professions, suggests a new study by the New York State Department of Health.
The study, published in the journal Occupational and Environmental Medicine, involved 8,977 cases of birth defects and 3,833 healthy controls from the National Birth Defects Prevention Study.
On analyzing mothers of around 9,000 children with birth defects, the researchers observed that certain abnormal birth conditions were more likely to be found in children of janitors, pharmacists or biological and chemical scientists.
“Given those job titles, one would expect those women to work with different chemicals or something that could possibly be an exposure,” said lead author Michele Herdt-Losavio from the New York State Department of Health.
Depending on the profession of the mother, the baby could be born with any of the physical defects, which are not related to the DNA, found Dr. Herdt-Losavio and her colleagues after studying 45 specific birth defects among mothers with 24 different occupations.
Women working as janitors were found to be more likely to give birth to a child with one or more of the defects including ear and eye defects, musculoskeletal problems, gastrointestinal problems, oral clefts and various other defects.
However, not all women working as janitors face similar risks, as Dr. Herdt-Losavio said, “There’s lots of questions that can be asked…. What do you do as a janitor? What products do you use? What hours do you work? How many hours do you work?”
The researchers, however, did not probe the probable reasons for this association between the birth defect of a child and his mother’s profession but they did offer a possible reasoning.
“What we can guess by looking at these job titles is that … it’s possible that they work with chemicals,” said Dr. Herdt-Losavio. “It’s not possible to say what those chemicals might be, or how much they might work with. But what we can do is point other [researchers] in the direction and give them some idea of where they might want to dig further and collect more data.”
- Heavy caffeine intake may mean smaller babies
Pregnant women who down six coffee cups’ worth of caffeine every day may have smaller babies than those who consume less caffeine, a new study finds.
Researchers found that among more than 7,300 Dutch women followed from early pregnancy onward, between 2 and 3 percent said they consumed the caffeine equivalent of six cups of coffee per day during any trimester. On average, their babies’ length at birth was slightly shorter than that of newborns whose mothers had consumed less caffeine during pregnancy.
Heavy caffeine consumers also had an increased risk of having a baby who was small for gestational age — smaller than the norm for the baby’s sex and the week of pregnancy during which he or she was born.
That finding, however, was based on a small number of babies, and the significance is uncertain. Of 104 infants born to women with the highest caffeine intakes, seven were small for gestational age.
The findings, reported in the American Journal of Clinical Nutrition, add to the conflicting body of research into whether caffeine during pregnancy affects fetal growth.
Some studies, for instance, have linked regular caffeine consumption during pregnancy — even a relatively modest one or two cups of coffee a day — to an increased risk of low birth weight. But other studies have found no such effects. Researchers have also come to conflicting conclusions as to whether caffeine affects the risk of miscarriage.
In this latest study, Rachel Bakker and colleagues at Erasmus Medical Center in Rotterdam used ultrasound scans to monitor fetal growth over the course of pregnancy in 7,346 women.
At each trimester, the women reported on their usual intake of coffee and tea. Most women consumed less than the equivalent of four cups of coffee per day at any point in pregnancy, but between 2 and 3 percent downed six or more cups’ worth of caffeine.
Overall, babies born to heavy caffeine consumers were slightly shorter, on average, at birth and during all three trimesters of fetal development, based on the ultrasound tests.
“Caffeine intake seems to affect length growth of the fetus from the first trimester onwards,” Bakker told Reuters Health in an email.
The implication, she said, is that pregnant women should not consume more than six cups of coffee per day. However, the findings also do not mean that less coffee is generally “safe” during pregnancy.
“We only studied the effect of caffeine on fetal growth,” Bakker said. “Future studies on possible other effects of maternal caffeine intake are therefore needed.”
Given the uncertainty about whether and how caffeine might affect pregnancy and fetal development, experts generally recommend that to be safe, pregnant women limit their intake.
The March of Dimes, for example, suggests that, based on research into miscarriage risk, pregnant women get no more than 200 milligrams of caffeine per day — roughly the amount in 12 ounces of coffee.
- Too little weight gain risky in twin pregnancy
Women pregnant with twins should be sure to gain the recommended amount of weight, according to a new study, which shows that gaining less weight than recommended during a twin pregnancy ups the risk of early birth and low weight babies.
“A woman should gain about a pound a week; less than that, and we had smaller babies and more pre-term births,” Dr. Nathan Fox of Maternal-Fetal Medicine Associates of New York City told Reuters Health.
Fox and his partners wanted to know if the twin pregnancy weight gain guidelines updated by the Institute of Medicine in 2009 made a difference in pregnancy outcomes.
These recommendations suggest a range of weight gain depending on a woman’s weight at the start of her twin pregnancy. A normal weight woman should gain 37 to 54 pounds; an overweight woman, 31 to 50 pounds; and an obese woman, 25 to 42 pounds.
In looking at 281 mostly normal weight women pregnant with twins, Fox and colleagues found that women who gained the recommended amount of weight did much better in regards to the pregnancy outcomes.
Women who gained less than the recommended amount of weight were more likely to give birth early (before 32 weeks of pregnancy) than women who gained the correct amount of weight (14 percent versus 5 percent). They were also more likely to give birth to smaller babies.
Unlike in singleton pregnancies, gaining enough weight in twin pregnancies can be Herculean task. “It’s often not easy,” Fox said. “We send our patients to nutritionists and have them on high calorie diets a lot to have them gain the right amount of weight. It’s not easy for many (women).”
About 3 in every 100 pregnancies is a twin pregnancy, the investigators note, and preterm births occur about 60 percent of the time, making the issue of correct weight gain even more important.
The strong link between inadequate weight gain in twin pregnancies and increased rates of pre-term birth “has not been conclusively demonstrated previously,” the investigators point out in the journal Obstetrics & Gynecology.
Their findings, they say, shed light on the importance on what “could be a correctable cause of prematurity in twins,” they conclude.
