The Royal College of Midwives (RCM) said there has been a rise in unvaccinated pregnant women being admitted to Scottish maternity units with severe Covid-19 symptoms.
Becoming ill with the virus can have “serious” consequences for both mother and baby, the college said.
The warning comes after reports from heads of midwifery in Scotland that vaccine uptake among pregnant women is low.
UK director for professional midwifery at the RCM, Dr Mary Ross-Davie, said: “Having Covid-19 during pregnancy, particularly in the later stages, can have serious consequences for both mothers and their babies.
"It can double the chance of stillbirth and triples the chance of a preterm birth, which can have a long-term health impact for the baby.
"We know that the vaccine is a safe and effective way of preventing this, with hundreds of thousands of pregnant women worldwide having been vaccinated.
"We recognise that, until fairly recently, the advice has sometimes felt confusing, which is why we want to reassure women that there are now numerous studies confirming the safety of the vaccine, both for you and your baby.”
In an update published on Monday, the Medicines and Healthcare products Regulatory Agency (MHRA) found there was no evidence to suggest Covid vaccines affect fertility or the ability to have children.
The regulator said: “There is no pattern from the reports to suggest that any of the Covid-19 vaccines used in the UK, or any reactions to these vaccines, increase the risk of miscarriage or stillbirth.
“There is no pattern from the reports to suggest that any of the Covid-19 vaccines used in the UK increase the risk of congenital anomalies or birth complications.”
The MHRA said it was also reviewing reports of the impact of the vaccine on menstrual cycles and vaginal bleeding, but has so far found nothing to support a link, saying: “The menstrual changes reported are mostly transient in nature”.
Figures published by Public Health Scotland last month showed almost 4,000 pregnant women had received a Covid vaccine, with no adverse effects reported.