Constipation is a common problem during pregnancy. It is essential to relieve the condition without putting the developing child at risk or further stressing the mother. The fact that lactulose is not absorbed in the small intestine is of great significance when treating constipation during pregnancy, as it presents no threat to the foetus. Lactulose also does not appear in breast milk so that the treatment can also be continued during nursing. The present study was an open base-line controlled study to show the efficacy, safety and acceptability of dry lactulose (Duphalac Dry) in pregnant women suffering from chronic or occasional constipation. It was a multi-center study in 12 gynecological practices. 62 women aged between 19 and 40 years were treated during 4 weeks with lactulose. 34% had chronic constipation and the remaining 66% constipation due to the pregnancy. The main criteria for efficacy were frequency of defecation and consistency of stools. There was overall judgement of the efficacy by patients and doctors. Safety was assessed by the number of reported side-effects and compared to the reported concomitant symptoms before treatment. Here also, the patients and their doctors gave a global impression. In addition, patients rated the product flavor and administration methods. The frequency of defecation was significantly increased after 1 week (4.0 vs. 2.5 [median per week], p < 0.001) and normalized after 2 weeks (6 stools per week). Also, the consistency of the stools was normalized during the treatment. The global assessment of efficacy by the treating physicians was good or very good in 84% of the cases and by the patients in 81%.(ABSTRACT TRUNCATED AT 250 WORDS)