Greater Maternal Weight Gain Advocated for Twins

OB/GYN News, Oct 1, 2001 by Bruce Jancin

STANFORD, CALIF. - The time has come to seriously consider encouraging weight gains of 45-50 pounds or more as "best practice" in twin pregnancies, Judith E. Brown, Ph.D., said at a conference on perinatal and pediatric nutrition.

"In talking about weight gains of 50 pounds or more, I know I might get nasty stuff thrown at me at any moment. There's a huge sentiment out there, particularly among obstetricians but also some nutritionists, that women are gaining far too much weight now under the Institute of Medicine recommendations" calling for weight gains of 35-45 pounds in twin pregnancies, noted Dr. Brown, professor of public health nutrition at the University of Minnesota, Minneapolis.

She argued that the optimal birth weight of twins is 3,000-3,500 g, as that's what is associated with the lowest perinatal mortality. Those birth weights, however, are far above the current national average for twins, which is roughly 2,400 g. Fifty-four percent of twins are low birth weight, defined as less than 2,500 g.

"We have a long way to go to improve the health of infants in this country. We still have 7.8% low birth weight, 11.9% preterm delivery, and although average birth weights are increasing we're being beaten down by lower gestational age. If we don't do something to shift this distribution we're going to stay right where we are. One of those things would be to optimize the rate of weight gain and total gain in women who have multifetal pregnancies. And that might mean talking about a 45-to 50-pound gain," she said at the conference, which was jointly sponsored by Symposia Medicus and Stanford University.

Dr. Brown cited new data from the University of Minnesota's Diana II Project, a study of 570 twin pregnancies, 48% of which ended with optimal neonatal outcome, defined as both babies having birth weights in excess of 2,500 g. In that study, the highest rate of optimal pregnancy outcome-57%--occurred in women having a pregnancy weight gain in excess of 45 pounds.

In contrast, only 48% of women who gained 35-45 pounds had two babies weighing more than 2,500 g each, as did 35% of women who gained less than 35 pounds.

In a multiple regression analysis looking at quartiles of total pregnancy weight gain, the average birth weight of twin pairs whose mother gained 50 pounds or more was 2,699 g, compared with 2,599 g for women who gained 41-50 pounds, 2,410 g for those who gained 31-41 pounds, and 2,255 g for women who gained less than 31 pounds.

Only 35% of women who gained an average of less than 0.9 lb/wk throughout pregnancy had an optimal pregnancy outcome. So did 45% of those who gained 0.9-1.2 lb/wk, 55% of women who gained 1.2-1.5 lb/wk, and 53% of those who put on more than 1.5 lb/wk.

Several maternal characteristics were related to the probability of optimal twin pregnancy outcome. (See box.) Women who had undergone fertility treatment were significantly less likely to give birth to two babies weighing more than 2,500 g. So were women who were unmarried, nonwhite, or who lacked a high school degree. Women who were underweight before pregnancy, as defined by a body mass index below 19.8 kg/[m.sup.2], or who were normal weight had lower rates of optimal pregnancy outcome than those having a prepregnancy BMI greater than 26 kg/[m.sup.2].

In contrast, there was no difference in the probability of optimal pregnancy outcome regardless of whether the mother had gestational diabetes, preeclampsia, hyperemesis, or more than 18 days of vomiting.

Detailed food frequency questionnaires indicated that women with optimal newborn outcomes consumed an average of 2,359 kcal/day-273 kcal more than those with nonoptimal outcomes.

Based upon data from Diana II and other studies, Dr. Brown said women carrying twins should be urged to gain about 6 pounds during the first trimester and 1.51.7 lb/wk thereafter.

"You can't really say, 'It's okay to lose weight in the first part of pregnancy if you gain it later.' That's antiquated advice. ... It turns out early weight gain is important. That's a shame because women with multifetal pregnancies often don't know that information until after the first trimester. I think we need to get to women with this advice before they become pregnant."

Factors Affecting Twin Birth Weights

                          Effect on average birth
Factor                    weight of each twin

Each maternal BMI unit
increase                  Increased by 109 g
Parous mother             Increased by 84 g
Each day of gestational
age                       Increased by 23 g
Each 1 pound of maternal
weight gain in pregnancy  Increased by 5 g
Maternal history of
fertility treatment       Reduced by 75 g
Female gender             Reduced by 102 g
Monozygotic twins         Reduced by 135 g

Source: Diana II Project