Betamimetics for suspected impaired fetal growth

Too little evidence to show whether betamimetic drugs for women during pregnancy benefits unborn babies who are smaller than expected.

Betamimetic drugs such as ritodrine relax muscles and help the body break down sugar found in fruit and meat (glucose) for energy. It has been thought that betamimetic drugs taken by mouth or injection by women who are more than 27 weeks' pregnant may improve the growth of unborn babies who are smaller than expected (impaired fetal growth). The review of two trials (118 women) has found too little evidence to show whether the unborn baby's growth improves when the mother takes betamimetic drugs. More research is needed into the short and long-term effects of betamimetic drugs on women and their babies.

Authors' conclusions: 

Larger, well-designed studies are needed to evaluate the effects of betamimetics on fetal growth. Since there is potential for adverse effects due to the pharmacological characteristics of this group of drugs, data related to any potential harms should be collected in addition to beneficial effects.

Read the full abstract...

Betamimetic drugs may promote fetal growth by increasing the availability of nutrients and by decreasing vascular resistance. They may also induce adverse effects via their effects on carbohydrate metabolism.


The objective of this review was to assess the effects of betamimetic therapy for suspected impaired fetal growth on fetal growth and perinatal outcome.

Search strategy: 

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (June 2009).

Selection criteria: 

Randomized trials of betamimetic therapy compared with no betamimetic therapy or placebo in women with suspected impaired fetal growth.

Data collection and analysis: 

Eligibility and trial quality was assessed.

Main results: 

Two studies of 118 women were included. No statistically significant differences were found between the betamimetic groups and the control groups for low birthweight (risk ratio 1.17, 95% confidence interval 0.75 to 1.83), other anthropometric measures or neonatal morbidity and mortality.