To study supplementation effect of vitamin K (VK) alone or combined with other nutrients administered to pregnant women, we searched Cochrane Pregnancy and Childbirth Group's Trials Register (till 22 January 2016, updated on 28 February 2018) including other resources. Two review authors independently assessed randomised or quasi-randomised controlled trials for inclusion, data extraction, accuracy, and risk of bias. We included older trials from high-income countries (six; 21,493 women-newborns), judged mostly as high or unclear bias risk. We could not assess high-risk e.g. epileptic women, but healthy women (different gestational ages) received varying VK dosages and duration. We meta-analysed neonatal bleeding (RR 1.16, 95% CI 0.59 to 2.29; P = 0.67) and maternal plasma VK1 (MD 2.46, 95% CI 0.98 to 3.93; P = 0.001). We found many outcomes were un-assessed e.g. perinatal death, maternal bleeding, healthcare utilization. Mostly newborns were included where VK found significantly effective for e.g. serum VK (mother-newborn), maternal breast milk VK. Few trials reported neonatal adverse side effects. The GRADE evidence quality was very low i.e. neonatal bleeding, neonatal jaundice, maternal plasma VK1. The intervention was favourable for maternal sera VK1 but remained uncertain for neonatal bleeding and other outcomes. The existing literature gaps warrant future investigations on un-assessed or inadequately reported outcomes.