The authors conducted a prospective study of 4069 pregnant women, of whom 171 (4.2%) were diagnosed with GDM at 28 weeks or later. While fetal size at 20 weeks was not associated with a subsequent diagnosis of GDM, at 28 weeks babies of mothers with GDM were twice as likely to have an abdominal circumference above the 90th percentile (adjusted relative risk, 2.05; 95% CI, 1.37–3.07).
Maternal obesity showed similar associations with excessive fetal growth, and the combination of GDM at ≥28 weeks and maternal obesity led to an almost five-fold increase in risk (adjusted relative risk, 4.52; 95% CI, 2.98–6.85). Fetal abdominal circumference above the 90th percentile at 28 weeks was associated with an approximately four-fold risk of being large for gestational age at birth.
Ulla Sovio, the study’s first author, said: “Our study suggests that the babies of women subsequently diagnosed with gestational diabetes are already abnormally large by the time their mothers are tested for the disease. Given the risk of complications for both mother and child from GDM, our findings suggest that screening women earlier on in pregnancy may help improve the short- and long-term outcomes for these women.
“Early screening may be particularly beneficial for obese women, as fetal growth is already abnormal by 20 weeks among these women. Any intervention aimed at reducing the risk of abnormal birthweight in the infants of obese women may need to be implemented even earlier.”
Gordon Smith, a co-author, told BBC News: “The recommendations are that screening should take place at some point between 24 and 28 weeks, but in practice a lot screen at 28 weeks. Our findings indicate that it should be brought forward to 24 weeks and that would still be consistent with existing guidelines.”
However, it should be noted that the study did not show whether excessive growth could be identified at 24 weeks, and studies would be required to determine whether changing the screening date would reduce the risk.
The study can be read in full here.
