Background: Helminthiasis is infestation of the human body with parasitic worms and it is estimated to affect 44 million pregnancies, globally, each year. Intestinal helminthiasis (hook worm) is associated with blood loss and decreased supply of nutrients for erythropoiesis, resulting in iron-deficiency anaemia. Over 50% of the pregnant women in low- and middle-income countries suffer from iron-deficiency anaemia. Though iron-deficiency anaemia is multifactorial, hook worm infestation is a major contributory cause in women of reproductive age in endemic areas. Antihelminthics are highly efficacious in treating hook worm but evidence of their beneficial effect and safety, when given during pregnancy, has not been established. Objectives: To determine the effects of administration of antihelminthics for soil-transmitted helminths during the second or third trimester of pregnancy on maternal anaemia and pregnancy outcomes. Search methods: We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (31 January 2015) and reference lists of retrieved studies. Selection criteria: All prospective randomised controlled trials evaluating the effect of administration of antihelminthics during the second or third trimester of pregnancy. Data collection and analysis: Two review authors independently assessed trials for inclusion and risk of bias, extracted data and checked them for accuracy. Main results: A total of four trials including 4265 participants were included in this review. Two of the included trials were of high quality, while two were of relatively low quality with limitations and biases in design and conduct. Analysis showed that administration of a single dose of antihelminthic in the second trimester of pregnancy is not associated with any impact on maternal anaemia in the third trimester (risk ratio (RR) 0.94; 95% confidence interval (CI) 0.81 to 1.10; 3266 participants; four trials; low quality evidence). Subgroup analysis on the basis of co-interventions other than antihelminthic, which included iron supplementation given to both groups was also not associated with any impact on maternal anaemia (RR 0.76; 95% CI 0.47 to 1.23; 1290 participants; three trials; moderate quality evidence). No impact was found for the outcomes of low birthweight (RR 1.00; 95% CI 0.79 to 1.27; 3255 participants; three trials; moderate quality evidence), preterm birth (RR 0.88; 95% CI 0.43 to 1.78; 1318 participants; two trials, moderate quality evidence) and perinatal mortality (RR 1.09; 95% CI 0.71 to 1.67; 3385 participants; two trials; moderate quality evidence). None of the included studies reported impact on infant survival at six months of age. Authors' conclusions: The evidence to date is insufficient to recommend use of antihelminthic for pregnant women after the first trimester of pregnancy. More well-designed, large scale randomised controlled trials are needed to establish the benefit of antihelminthic treatment during pregnancy.