MATERNAL weight gain exceeds current guidelines in 47% of American pregnancies, according to a recent study, which also revealed that weight gain is below the recommended minimum in 21% of pregnancies.

Published in the April 2015 edition of the journal Obstetrics and Gynecology, the American study focused on women living in 28 states who carried a pregnancy to full term (minimum 37 weeks of gestation) during 2010 and 2011.

The researchers examined gestational weight gain in conjunction with various associated demographic, behavioral, psychological and medical factors. Insufficient or excessive weight gain was defined according to the Institute of Medicine's 2009 guidelines, which are relative to the mother's pre-pregnancy BMI.

Altogether, only 32% of the mothers met the official weight gain guidelines, meaning that 68% put on either too much or too little weight.

The researchers also found that, compared to the 52% of women with a normal BMI at the start of pregnancy, the 4% who were underweight before conception had a 50% lower risk of excessive weight gain. Conversely, women who were overweight (24%) or obese (12% with class 1 obesity, 5% with class 2, 4% with class 3) were twice as likely to gain too much.

Women who were either underweight or morbidly obese at the start of pregnancy carried a 25% higher risk of not gaining enough weight during gestation.

The study also highlights that most of the factors related to excessive or insufficient pregnancy weight gain were linked to demographic characteristics, including education level and ethnic group. Quitting smoking during pregnancy was also associated with excessive weight gain, particularly in those who were not underweight at conception.

Though the exact guidelines may vary between organizations and countries, most experts agree on the importance of gaining neither too much nor too little weight during pregnancy. Among other risks, excessive or insufficient maternal weight gain may impact the metabolism and appetite control of the child after birth.

A study published in 2014 in the American Journal of Obstetrics and Gynecology indicated that 20.5% of children born to mothers who exceeded weight gain recommendations during pregnancy were overweight or obese.