Infants of diabetic mothers have an increased incidence of congenital malformations, which now accounts for half the perinatal mortality. The incidence of malformations is significantly higher in White's classes D and F, in which the mothers have long standing diabetes or vascular complications, or both, than in the less severe classes A, B, and C. The authors have reported previously that some fetuses in early diabetic pregnancy are smaller than normal. In this paper, they present the results of a study which suggest that these fetuses carry a significantly higher risk of being malformed. Ninety-nine insulin-dependent diabetic women with regular menstrual histories were examined by ultrasonic scanning in the 7th and 14th week of pregnancy.Using data obtained from a series of normal pregnancies, the authors constructed a table that permitted estimation of fetal age from the crown-rump length. For each measurement of crown-rump length in the diabetic patients, the corresponding fetal age was read and compared with the age calculated by using the first day of the last menstrual period. The average of the differences between “ultrasound age” and menstrual age for each fetus was taken. Ninety-five per cent of the single determinations of crown-rump length in the normal series deviated by 5 days or less from the menstrual age. Thirty-eight of the 99 fetuses in the diabetic group were smaller than the lower limit of normal, which is highly significant. For this phenomenon, the authors suggest the term “early growth delay,” as opposed to the growth retardation seen in the third trimester in (for example) placental insufficiency.Fetuses with major congenital malformations were diagnosed at birth or in the first 10 days of life. Seven of the nine malformed fetuses were smaller than normal in early pregnancy (P 0.02). In one of them, the morphology of the malformation (a large sacral myelome-ningocele) may have influenced the determination of crown-rump length; the length may have been overestimated and the delay therefore underestimated. The effect of early growth delay and that of the well-established risk marker, severe maternal diabetes, enhance each other so that a considerably delayed fetus of a mother in White's class D or F has a risk of severe congenital malformation of six in 22, or 27 per cent (11 to 50 per cent, 95 per cent confidence interval).Comparison between the 38 pregnancies in which the fetus was too small in early pregnancy and the remainder of the pregnancies shows a difference in birth weight of 500 g (P 0.001) despite an almost identical gestational age at birth. Delayed fetuses on average were, in fact, 3 days older than the normal ones; but the ultrasound age, which takes the delay into account, showed the delayed fetuses to be 7 days younger than the unaffected ones. There was no difference in maternal height or parity between the two groups.
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