Severe and mild deformations in newborn infants of insulin dependent diabetic mothers (IDDMs) and control mothers were evaluated with respect to the types of anomalies and previously hypothesized constraint factors. Factors evaluated were gestational length, birth weight, corrected birth weight for gestation (weight ratio), maternal height and parity, and severe deformations. Newborn infants from 81 control and 133 insulin dependent diabetic pregnancies were recruited periconceptually as part of a larger study of diabetes in early pregnancy. Examinations were done at 48 to 72 hours of life by one examiner blinded to maternal status using a checklist of major and minor deformations and malformations. Mild deformations were found to be common and were present in 84% of newborn infants. Severe deformations occurred in three (1.4%) IDMs, with two of three newborn infants having major malformations involving the CNS and/or musculoskeletal system which affected fetal movement. There was no significant difference between IDMs and control newborn infants with respect to the number with deformations; however, fetal macrosomia was not present in study participants. Using the entire cohort, a significantly greater number of deformations were present in newborn infants with a gestation > 36 weeks (P < 0.001), birth weight > 3,000 g (P < 0.001), and weight ratio > or = 1.2 (P = 0.05). There was no significant association with primiparous mothers or women with a height < 165 cm and the presence of deformations. For gestational age and birth weight, mild deformations were apparent only after 33 weeks gestation (P << 0.001) and/or birth weights of 2.0 kg or more (P << 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)