You might have cravings for sweet treats while you’re pregnant, but a recent study shows that pregnant women who overindulge may be more likely to have a child with allergies or asthma. 
Researchers from Queen Mary University in London studied nearly 9,000 women who gave birth during the 1990s and their children. Compared to children whose mothers ate the least amount of sugar (less than 7 teaspoons daily), children born to moms who ate the most (16-69 teaspoons a day) were 73% more likely to be diagnosed with two or more types of allergies, and 101% more likely to have allergic asthma.
The scientists also looked at dust mites, cats, grass, and other allergens known to produce respiratory and skin problems. 
- 62% of the children studied did not have any allergic conditions, but the other children had one or more ailments or symptoms
- Approximately 22% of the children had a common allergy
- 16% had eczema
- 12% had asthma
- 11% had wheezing and whistling
- 9% had hay fever
No association was found between maternal high sugar consumption and children’s eczema or hay fever. And unlike in previous studies, no association was found between the children’s own sugar intake (at age 4) and any of their health outcomes at age 7. 
The study examined free sugars – both the added kind and the naturally occurring kind – including honey, syrups, and fruit juices. Foods containing the most free sugars include soda, jams, cakes, cookies, and fruit juices. Sugars in whole fruits and vegetables are not considered free sugars. 
The research, published in the European Respiratory Journal, is observational, and does not prove that high sugar consumption during pregnancy causes allergies and asthma. However, the researchers hypothesize that consuming a high-sugar prenatal diet triggers an allergic immune reaction that continues after birth, resulting in allergic inflammation in the baby’s developing lungs.
As researcher Annabelle Bedard notes, consumption of high fructose corn syrup increased to 30% of refined sugars consumed per capita in the U.S. between 1970 and 2000.
“The dramatic ‘epidemic’ of asthma and allergies in the West in the last 50 years is still largely unexplained – one potential culprit is a change in diet. Intake of free sugar and high fructose corn syrup has increased substantially over this period.
We know that the prenatal period might be crucial for determining risk of asthma and allergies in childhood and recent trials have confirmed that maternal diet in pregnancy is important.” 
In a press release, lead researcher Seif Shaheen said:
“We cannot say on the basis of these observations that a high intake of sugar by mothers in pregnancy is definitely causing allergy and allergic asthma in their offspring. However, given the extremely high consumption of sugar in the West, we will certainly be investigating this hypothesis further with some urgency.” 
If the findings can be replicated, Shaheen said, researchers will conduct a trial to determine whether it is possible to reduce allergies and allergic asthma by decreasing sugar intake in pregnant women.
Limiting sugar during pregnancy should always be a priority anyway, since failing to do so can lead to gestational diabetes, a condition that can result in babies having breathing difficulties, low glucose levels, and jaundice. 
 USA Today