Objective: To determine the oral health knowledge of pregnant women and to report their future plans to provide dental care for their expected child. Design and setting: Prospective cohort study; Ultrasound maternity services at St Thomas’ Hospital, London, 2014. Pregnant women attending for a routine ultrasound scan completed a questionnaire. Results: Women did not know that milk, dried fruit or fruit juices can cause caries. Most women knew about the benefit of fluoridated toothpaste, dental floss and sugar-free chewing gum, but only a minority knew about fluoride varnish. Most pregnant women planned to read or seek advice before purchasing their child’s first toothpaste. There was no difference regarding knowledge of prevention tools (diet and fluoride supplements) for dental caries (P>0.05) between first-time mothers and those who had children already. Though the latter knew more about toothpaste dose and timing of starting toothbrushing (P<0.05). Discussion: Oral health knowledge among pregnant women was deficient with respect to the cariogenicity of prolonged night-time milk feeding, dried fruits and fruit juice consumption. There was also limited knowledge of the benefit of fluoride varnish and timing of starting toothbrushing. Conclusions: Oral health knowledge amongst pregnant women is still deficient in many aspects. In this study population the need to improve maternal knowledge was shown.