Effect of terbutaline tocolysis on infant birthweight

Previous research has suggested that terbutaline sulfate increases serum glucose in pregnant women. Increases in serum glucose in women who have gestational diabetes mellitus often lead to the birth of larger infants. This study examines the effect on infant birthweight of terbutaline used as a tocolytic agent in otherwise normal term pregnancies.

An historical cohort study was conducted of all births in a 12-month period at a US Army community hospital. There were 1376 deliveries of all types; 481 of the patients were excluded for variables that influence gestational duration or fetal weight, and 5 patients' records were lost. Birthweights relative to gestational age were compared.

The two groups (women who were treated with terbutaline, n = 94; control group, n = 796) differed with respect to age (terbutaline group, 1.6 years younger, P = .002); pregravid weight (terbutaline group, 10.3 lb lighter, P < .001); and total weight gain (terbutaline group, 3.2 lb less, P = .001). The groups were comparable in all other variables studied (P > .05). Women receiving terbutaline therapy (average length of therapy, 4.7 weeks) gave birth an average of 1 week earlier than those not treated with terbutaline (39.09 weeks and 40.09 weeks, respectively, P < .001). The mean absolute birthweight of infants exposed to terbutaline in utero was less than that of infants from the control group (P < .001), but this difference (191.6 g) can be accounted for by the difference in average gestational age between the terbutaline group and the control group. There was no difference in birthweight (P > .05) when birthweight relative to gestational age was compared between the two groups.

Women in this study who were treated with terbutaline did not give birth to larger infants. The previously noted hyperglycemia in women receiving terbutaline may not have been present in this study population or may not have been significant enough to affect birthweight.