Gestational Diabetes: Ultrasounds Overestimate LGA Risk

Diedtra Henderson

October 12, 2015

Ultrasounds performed on women with gestational diabetes mellitus (GDM) overestimate the risk for large for gestational age (LGA) and, regardless of the infant's actual weight, increase the mother's odds for cesarean delivery, according to a retrospective cohort study published online October 5 in Obstetrics & Gynecology.

"The prevalence of both ultrasound-estimated fetal weight greater than 4,000 or 4,500 g and birth weight greater than 4,000 or 4,500 g was low in our contemporary population of women with GDM," write Christina M. Scifres, MD, from the Department of Obstetrics, Gynecology and Reproductive Sciences, Magee Women's Research Institute, University of Pittsburgh School of Medicine, Pennsylvania, and colleagues. "However, ultrasound diagnosis of LGA was common and it overestimated the proportion of neonates born LGA by birth weight standards regardless of interval from ultrasonography to delivery or maternal prepregnancy [body mass index]."

Some 32.3% of births in the United States are achieved through cesarean delivery, and the American College of Obstetricians and Gynecologists recommends cesarean delivery for women with diabetes when their fetuses are estimated to weigh more than 4500 g. However, Dr Scifres and colleagues note that ultrasounds "are neither adequately sensitive nor specific" to identify LGA fetuses.

The researchers examined the outcomes of 903 women with GDM who gave birth from January 2009 to October 2012 at Magee-Women's Hospital in Pittsburgh. The 248 women who had an ultrasound diagnosis of LGA were older, had slightly higher fasting values on their 100 g oral glucose tolerance tests, were less likely to be smokers, and were more likely to need treatment for their GDM.

Infants with ultrasound-diagnosed LGA were delivered on average at 38.4 weeks of gestation compared with 38.9 weeks for infants who were diagnosed as appropriate for gestational age (P <.001).

Of the 903 women, 74 (8.2%) delivered an infant that was LGA, 53 (6.4%) delivered an infant that was greater than 4000 g, and nine (1.0%) delivered babies that weighed more than 4500 g.

Ultrasound-diagnosed LGA was associated with an increased risk for cesarean delivery (adjusted odds ratio [OR] 3.13; 95% confidence interval [CI], 2.10 - 4.67; P < .001), after adjustment for potential confounders including birth weight, maternal age, body mass index category, race, hypertensive disorders of pregnancy, chronic hypertension, and nulliparity.

When the researchers restricted the analysis to women who experienced any type of labor, the ultrasound diagnosis of LGA remained significantly associated with cesarean delivery risk (adjusted OR, 2.13; 95% CI, 1.34 - 3.38; P < .001) after adjustment for the same covariates and the addition of induced labor.

Moreover, stratified analysis showed that ultrasound-diagnosed LGA carried a similarly elevated risk for cesarean delivery in infants with a birth weight between 2500 g (41.3%) and 3499 g (20.0%; OR, 2.82; 95% CI, 1.62 - 4.84, P < .001), and for infants with a birth weight between 3500 g (45.1%) and 4500 g (19.2%; OR, 3.47; 95% CI, 2.06 - 5.88, P < .001; Mantel-Haenszel test for homogeneity, P = .57).

The authors write that their research on a well-characterized population of women with GDM should "reassure" healthcare providers about the low prevalence of macrosomia. Previous work found the prevalence of birth weight greater than 4,500 g in women with GDM was just 1.1%

"Our findings indicate that ultrasound suspicion of fetal overgrowth increases risk for cesarean delivery in women with GDM, similar to data in populations without diabetes," the authors conclude. "Ultrasonography may be most useful if targeted proximal to delivery, and our findings demonstrate that health care providers must focus more on the actual estimated fetal weight as opposed to LGA status."

The study authors have disclosed no relevant financial relationships.

Obstet Gynecol. Published online October 5, 2015. Abstract

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