The due dates of the women the researches observed were between April 1, 1991, and December 31, 1992.
The researchers evaluated 5,246 of their children and the median age of the adolescent participants was about 15.5 years old.
The alcohol, drug and tobacco use habits of all the children were evaluated, which led researchers to link vegetarianism during pregnancy to an increased risk of substance abuse.
Study lead author Dr Joseph Hibbeln said that, while women are often advised to reduce their meat consumption, this can cause nutritional deficiencies that may affect the development of a baby's brain.
Most vegetarians have a B12 deficiency while pregnant, as the vitamin is mainly available from meats and shellfish.
Vitamin B12 is essential for the body to metabolize folic acid, a nutrient vital for the development of a healthy fetus.
Because of this, the implementation of vegetarian foods that are B12-rich along with more widespread use of supplements could prove beneficial for pregnant vegetarians.
Dr Hibbeln said: "Among Western populations infants of vitamin B12 deficient mothers have poor brain growth, developmental regression, irritability, thrive poorly and demonstrate residual deficits in cognitive and social development."
New Zealand nutritionist Lee-Anne Waan says despite the findings being from a new study which she predicts people will disagree with, "as a new mother myself I would not be prepared to take such a risk without having all the knowledge I could."
"The foods we eat while pregnant and even breastfeeding have a significant impact on a child's growth and development."
Waan says the impact can be from something as simple as the child's food preferences aligning with what the mother consumed while pregnant to "far more important aspects of cognitive development and immunity".
"It makes sense that if we restrict certain nutrients or are deficient in any way, whether it be from a chosen lifestyle or other factor, the possibility of negative physical or physiological results is very real now and in the future."
Waan notes "having sufficient animal products in the diet ensures optimal B12, Vitamin A and D as well as important minerals like zinc- if your fuel is lacking or missing in anything something is going to go wrong somewhere."
She doesn't believe the answer lies in asking people to change their preferences but rather that "we become highly educated in our choices.
"If you wish to be a vegetarian then know everything you can about it. Education is paramount to mums-to-be and new mothers to ensure every child has the nutrients needed to grow and develop.
"If we adopt a particular diet or lifestyle we need to make sure we account for any deficiencies with supplementation. The price is simply too high to pay not too."
HOW TO GET ENOUGH NUTRIENTS WHILE ON A VEGETARIAN DIET
Reasons for taking up a vegetarian diet are varied, but the lifestyle has been proven to reduce one's risk of diabetes, heart disease and certain cancers.
However, many vegetarians consume too many processed foods, according to the Mayo Clinic.
The clinic recommends taking steps to counter harsh side effects of a vegetarian diet, including the following:
• include a wide variety of foods in your diet.
• consume enough calcium, B12 and vitamin D.
• eat enough protein in the form of foods such as eggs, dairy products, nuts, seeds and whole grains.
- Additional reporting, NZ Herald