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During the past 20 years, the incidence of multiple births in the United States has risen dramatically as a result of the use of assisted reproductive technologies and a trend toward delaying childbirth (1). Although infants of twin gestations represent only about 2% of all live births in the United States, compared with singletons they are 5 times more likely to be born premature (<37-week gestation), 9.5 times more likely to be very low birth weight (<1,500 g), and 8.5 times more likely to be low birth weight (<2,500 g) (2). At every gestational age, twins with greater birth weights have lower morbidity and mortality rates than their smaller counterparts (3,4). A growing body of clinical research indicates that maternal nutrition may play an important role in twin birth weight, particularly maternal pregravid weight and gestational weight gain (5-8). The 1990 report from the National Academy of Sciences, Nutrition During Pregnancy (9), recommended maternal weight gains of 35 to 45 lb for twin gestations.
Previous research has suggested that the optimal outcome for twin pregnancies is birth weights between 2,500 and 2,800 g at 35 to 38 weeks of gestation (4). One of the objectives of the current study was to evaluate maternal factors, including pregravid weight and gestational weight gain, associated with this "ideal" outcome. As part of a multiyear, anonymous field survey of maternal nutrition and the childhood growth of twins at the annual Twins Days Festival, mothers of twins were interviewed regarding their age at the twin birth, education, smoking status, recommended and actual weight gain, expected vs actual delivery dates, and the birth weights and genders of their twins. This study was approved by the Human Investigation Committee at Johns Hopkins University, the institution of the principal investigator at the time of initiation of the study.
The Twins Days Festival, which is held annually during the first weekend of August in Twinsburg, Ohio (about 30 miles south of Cleveland), includes children and adults of multiple gestations and their families. The nutrition component of this study was conducted during 1989, 1990, 1991, and 1993 and involved interviews with 924 mothers of twins and information on their 1,848 twin children. The interview included questions on maternal age and pregravid weight before the twin pregnancy, height, education, smoking status, recommended and actual gestational weight gain, expected and actual delivery dates, and the birth weights and genders of the twins. All families surveyed were white. Body mass index (BMI) was calculated on the basis of height and pregravid weight and modeled as continuous and categorical variables (underweight, normal weight, overweight, and obese) according to the recommendations of the National Academy of Sciences (9). Actual weight gain was modeled as continuous and categorical variables (<3 5 lb, 35 to 45 lb, >45 lb) and as less than, equal to, and greater than the recommendations of the National Academy of …